Chapter 3 - Genetic Analysis of single genes Flashcards
(573 cards)
1
Q
A diploid can have up to two different alleles at a single locus. Explain
A
A diploid organism (like humans) has two sets of chromosomes, one from each parent.
A locus is the physical location of a gene on a chromosome.
Therefore, each locus in a diploid can carry two alleles (versions of a gene)—one on each homologous chromosome.
During meiosis, alleles at each locus segregate so that each gamete (sperm or egg) receives only one allele.
2
Q
Phenotype depends on the alleles that are present, their dominance relationships, and sometimes also interactions with the environment and other factors. Explain
A
A phenotype is the observable trait (e.g., eye color, height).
It is determined by:
The genotype (specific alleles present),
The dominance (e.g., dominant vs. recessive),
And sometimes environmental factors (e.g., temperature affecting fur color in rabbits).
3
Q
Classical geneticists make use of true breeding lines, monohybrid crosses, Punnett squares, test crosses, reciprocal crosses, and the chi-square test.
A
True breeding lines: Organisms that produce offspring with the same traits when self-crossed.
Monohybrid cross: A cross between two individuals with different alleles for a single gene.
Punnett square: A grid to predict allele combinations and probabilities in offspring.
Test cross: Used to determine the genotype of an individual showing a dominant trait.
Reciprocal cross: Switches the sex of the parent with a given trait to test sex-linkage.
Chi-square test: A statistical method to test if observed results fit expected ratios (e.g., 3:1 or 9:3:3:1).
4
Q
True breeding lines:
A
Organisms that produce offspring with the same traits when self-crossed.
5
Q
Monohybrid cross:
A
A cross between two individuals with different alleles for a single gene.
6
Q
Punnett square:
A
A grid to predict allele combinations and probabilities in offspring.
7
Q
Test cross:
A
Used to determine the genotype of an individual showing a dominant trait.
8
Q
Reciprocal cross:
A
Switches the sex of the parent with a given trait to test sex-linkage.
8
Q
Chi-square test:
A
A statistical method to test if observed results fit expected ratios (e.g., 3:1 or 9:3:3:1).
9
Q
Sex-linked genes are an exception to standard Mendelian inheritance. Their phenotypes are influenced by the type of sex chromosome system and the type of dosage compensation system found in the species.
A
Sex-linked genes (often on the X chromosome) do not follow typical Mendelian ratios.
Males (XY) have only one X, so they express X-linked traits even if they’re recessive.
Dosage compensation mechanisms (like X-inactivation in females) ensure balance of gene expression between sexes.
The system can vary across species (e.g., XY in humans, ZW in birds).
10
Q
The male/female phenotype (sex) can be determined by chromosomes, genes, or the environment.
In many species:
A
Chromosomes (like XY or ZW) determine sex.
Genes (like SRY on Y chromosome in humans) trigger male development.
In some species, environment plays a role (e.g., temperature in reptiles determines sex of hatchlings).
11
Q
How many alleles can a diploid organism have at a single gene locus?
A
A: Two alleles—one on each homologous chromosome.
12
Q
What ensures each gamete gets one allele from each gene pair during gamete formation?
A
A: Meiosis.
13
Q
What three factors influence phenotype?
A
A: Alleles present, dominance relationships, and environmental interactions.
13
Q
What is a Punnett square used for?
A
A: Predicting allele combinations and phenotypic ratios in offspring.
14
Q
What is a test cross?
A
A: A cross with a homozygous recessive individual to determine an unknown genotype.
14
Q
What is a reciprocal cross used to detect?
A
A: Sex linkage of a gene.
14
Q
What does the chi-square test evaluate in genetics?
A
A: Whether observed data match expected Mendelian ratios.
15
Q
Why are sex-linked traits exceptions to Mendel’s laws?
A
A: Because they behave differently depending on the sex chromosome system and dosage compensation.
16
Q
Give an example of dosage compensation.
A
A: X-inactivation in female mammals.
17
Q
What factors can determine sex in an organism?
A
A: Chromosomes, specific genes, or environmental factors.
18
Q
Allele
A
A variant form of a gene found at a specific locus on a chromosome.
18
Q
Mendel’s First Law
Also known as the Law of Segregation;
A
states that each organism carries two alleles for a trait, which segregate during gamete formation.
18
Q
Homozygous
A
Having two identical alleles at a particular gene locus (e.g., AA or aa).
19
Law of Equal Segregation
Each gamete receives one of the two alleles with equal probability during meiosis.
19
Heterozygous
Having two different alleles at a particular locus (e.g., Aa).
20
Hemizygous
Having only one allele for a gene in a diploid organism (e.g., X-linked genes in males).
21
Wild-type
The most common or naturally occurring allele in a population.
21
Variant
An allele that differs from the wild-type, may or may not cause a change in phenotype.
22
Locus
The physical location of a gene on a chromosome.
23
Genotype
The genetic makeup (alleles) of an organism.
24
Phenotype
The observable physical or biochemical characteristics of an organism
25
Dominant
An allele that masks the effect of a recessive allele when present.
26
Recessive
An allele that is masked by a dominant allele; expressed only when homozygous.
27
Complete dominance
When one allele completely masks the effect of another.
28
Incomplete (semi) dominance
A situation where the heterozygous phenotype is intermediate between both homozygous phenotypes.
29
Co-dominance
Both alleles in a heterozygote are fully and separately expressed (e.g., AB blood type).
30
ABO blood group
A blood typing system involving co-dominant A and B alleles and recessive O.
30
Haplosufficiency
One copy of a gene is sufficient to produce a normal phenotype.
31
Haploinsufficiency
One copy of a gene is not enough for normal function, causing a mutant phenotype.
32
Classical genetics
The study of inheritance patterns through crosses and phenotype observations.
32
Molecular genetics
The study of gene structure and function at the molecular level (e.g., DNA, RNA, proteins).
33
True breeding lines
Organisms that consistently produce offspring with the same phenotype when self-crossed.
34
Monohybrid cross
A cross between individuals focusing on a single gene trait.
35
Punnett Square
A diagram used to predict the genotypes and phenotypes of offspring.
36
test cross
A cross between an individual of unknown genotype and a homozygous recessive individual to determine the unknown genotype.
37
Tester
The homozygous recessive individual used in a test cross.
38
Sex-linked
Genes located on sex chromosomes (usually X or Y).
39
Dosage compensation
Mechanism to balance gene expression between sexes despite differing numbers of sex chromosomes (e.g., X-inactivation in females).
40
X-linked genes
Genes located on the X chromosome.
40
Autosomal genes
Genes located on non-sex chromosomes.
41
Reciprocal cross
A pair of crosses in which the phenotypes of the male and female are reversed to test for sex linkage.
42
Z-linked genes
Genes located on the Z chromosome (common in birds, butterflies, etc., with ZW sex determination).
42
Hermaphrodites
Organisms that possess both male and female reproductive organs.
43
Parthenogenesis
A form of asexual reproduction where offspring develop from an unfertilized egg.
44
Hormonal
Traits or processes influenced by hormones (e.g., sexual development).
45
Cell-autonomous
When a gene’s effect is limited to the cell in which it is expressed.
46
Sexual gynandro-morphs
Individuals with both male and female physical characteristics due to genetic mosaicism.
47
Sexually dimorphic
Species where males and females have distinct phenotypes.
48
Gynandromorphy
Condition where an organism contains both male and female tissues.
49
Mosaic
An individual with two or more genetically distinct cell lines originating from one zygote.
50
Chimera
An individual composed of cells from two or more different zygotes.
51
G + E = P
Genotype + Environment = Phenotype; shows that phenotype results from both genes and environment.
52
Penetrance
The percentage of individuals with a particular genotype that actually express the associated phenotype.
52
Expressivity
The degree or intensity to which a genotype is expressed in a phenotype.
53
Sampling effects
Random effects in small populations that can influence genetic outcomes (e.g., genetic drift).
54
Chi-square χ² test
A statistical test used to compare observed data with data expected under a specific hypothesis.
55
What is an allele?
A different version of a gene found at the same locus on a chromosome.
56
What does Mendel’s First Law state?
It states that two alleles for a gene segregate during gamete formation, and each gamete receives one allele with equal probability.
57
What is the Law of Equal Segregation?
The principle that each gamete carries only one allele for each gene due to the separation of alleles during meiosis.
58
What did Mendel use to discover genetic laws?
Pea plants with contrasting traits (e.g., round vs. wrinkled seeds).
59
Which seed color allele is dominant in peas?
Yellow.
60
What is the difference between phenotype and genotype?
Genotype is the genetic makeup (alleles); phenotype is the physical expression of the trait.
61
In Mendel’s pea plants, what are the two forms of flower color?
Purple (dominant) and white (recessive).
62
What happens to alleles during meiosis according to Mendel’s law?
They segregate so that each gamete receives one of the two alleles.
63
Give an example of a heterozygous genotype for seed form.
Rr (Round is dominant over wrinkled).
64
What ensures equal segregation of alleles?
The process of meiosis during gamete formation.
65
Fill in the blank: Each trait exists in two versions called _______.
[alleles]
66
List the dominant forms of the traits studied by Mendel.
* Round (Seed Form)
* Yellow (Seed Color)
* Purple (Flower Color)
* Inflated (Pod Form)
* Green (Pod Color)
* Axial (Flower Position)
* Tall (Stem Length)
67
True or False: The alleles are blended during inheritance.
False.
68
What is a heterozygous plant for seed color?
A plant with one yellow allele and one green allele.
69
What is the recessive form of pod color in Mendel's studies?
Yellow.
70
Fill in the blank: Mendel studied _______ traits in pea plants.
[seven]
71
What is the dominant form of stem length in Mendel's experiments?
Tall (long).
72
What does 'diploid' mean?
Having two sets of chromosomes—one from each parent.
73
What does it mean to be homozygous for a gene?
Both alleles at a locus are the same (e.g., AA or aa).
74
What does it mean to be heterozygous for a gene?
The two alleles at a locus are different (e.g., Aa).
75
What is hemizygosity?
Having only one allele present at a gene locus instead of two, often seen in males for X-linked genes.
76
Can a diploid individual carry more than two alleles of the same gene?
No, only two alleles per gene, but populations can have many.
77
What is the wild-type allele?
The most common, typically functional allele in a population.
78
What is a variant allele?
An allele with a DNA sequence difference that may still produce a normal phenotype.
79
What is a mutant allele?
An allele that results in an altered phenotype, often due to a disruptive DNA change.
80
What is an allelic series?
A set of multiple alleles at the same gene locus, including wild-type and various mutant forms.
81
Give an example of hemizygosity in humans.
Males are hemizygous for genes on the X chromosome.
82
What does diploid mean?
Having two sets of chromosomes—one from each parent.
83
What are homologous chromosomes?
Chromosome pairs in a diploid organism.
84
What is homozygous?
Both alleles at a gene locus are the same (e.g., AA or aa).
85
What is the trait expression in homozygous individuals?
Trait expression is consistent.
86
What is heterozygous?
The two alleles at a gene locus are different (e.g., Aa).
87
How does trait expression work in heterozygous individuals?
Trait expression may depend on dominance.
88
What is hemizygous?
Only one allele is present at a locus.
89
What causes hemizygosity?
Gene deletion or sex chromosomes in males.
90
What is a wild-type allele?
The most common version of the gene in the population.
91
What are variant alleles?
Alleles that differ in DNA sequence but may produce a normal phenotype.
92
What are mutant alleles?
Alleles that differ in function or appearance, possibly causing visible differences or disease.
93
What is an allelic series?
A collection of multiple alleles at the same gene locus.
94
Fill in the blank: A diploid cell has ______ alleles of each gene.
two
95
True or False: A population can contain many different alleles of the same gene.
True
96
What does the term 'allelic diversity' refer to?
The variety of alleles present in a population.
97
What is the significance of sex chromosomes in hemizygosity?
In males, X-linked genes are hemizygous due to having only one X chromosome.
98
What is the relationship between alleles and phenotype?
Alleles can influence the phenotype expressed in an organism.
99
What is a locus?
The specific physical location of a gene on a chromosome
## Footnote
Locus refers to the position, not the gene itself.
100
What is an allele?
A specific version or form of a gene found at a particular locus
## Footnote
Diploid organisms have two alleles per locus.
101
What does genotype refer to?
The complete set of alleles that an individual has at all loci of interest
## Footnote
Typically written only for the genes/loci being studied.
102
Define phenotype.
The observable or measurable trait—how the genotype expresses itself in the organism
## Footnote
Includes simple traits like hair color and complex traits like intelligence.
103
What are the types of traits included in phenotype?
* Simple traits: hair color, eye color
* Complex traits: disease susceptibility, behavior, intelligence
104
How does phenotype result?
From the interaction between alleles and sometimes with the environment
105
What is gene interaction?
When two different alleles are present, they may interact in dominant, recessive, co-dominant, or incomplete dominance ways
## Footnote
These interactions affect how the phenotype appears.
106
True or False: The terms gene and locus are used interchangeably.
False
107
Fill in the blank: A _______ is one allele per chromosome at a locus.
locus
108
Fill in the blank: The genotype typically includes only the genes/loci being _______.
studied
109
What is a locus?
A specific position on a chromosome where a gene is located.
110
What is an allele?
A version or form of a gene at a particular locus.
111
What is a genotype?
The complete set of alleles at all loci of interest in an organism.
112
When writing out a genotype, what do we usually include?
Only the alleles at the loci of interest; other loci are assumed to be wild-type.
113
What is a phenotype?
The observable characteristics or traits resulting from an organism's genotype.
114
What can phenotypes range from?
Simple traits like hair color to complex traits like disease risk or behavior.
115
What happens when two alleles are present at a locus?
They may interact in various ways that influence the phenotype.
116
Can the environment influence phenotype?
Yes, especially in complex traits like behavior or disease susceptibility.
117
What is the phenotype of AA (homozygous dominant) in Mendel's pea study?
Purple flowers
118
What is the phenotype of aa (homozygous recessive) in Mendel's pea study?
White flowers
119
What is the phenotype of Aa (heterozygous) in Mendel's pea study?
Purple flowers
120
What does it mean when a dominant allele is present in a heterozygote?
The dominant allele masks the expression of the recessive allele
121
How is a dominant allele represented in genetic symbolism?
Uppercase letter (A)
122
How is a recessive allele represented in genetic symbolism?
Lowercase letter (a)
123
What notation is used to show different variants or multiple alleles?
Superscripts (e.g., a⁺, a¹)
124
What does a⁺ usually indicate in genetic notation?
The wild-type allele
125
What does forward slash notation (e.g., AA or A/A) signify?
Both alleles are at the same gene locus but on homologous chromosomes
126
In the context of Drosophila melanogaster, what does the white gene encode?
A protein called WHITE
127
True or False: In a heterozygous individual, the recessive phenotype is visible.
False
128
Fill in the blank: The dominant allele is represented by a _______.
Uppercase letter
129
Fill in the blank: The recessive allele is represented by a _______.
Lowercase letter
130
What is complete dominance?
A condition where one allele completely masks the effect of another in a heterozygote.
## Footnote
This is a key concept in Mendelian genetics, illustrating the relationship between alleles in heterozygous individuals.
131
What is the phenotype of a heterozygote in complete dominance?
The same as the dominant homozygote (e.g., Aa = AA = purple flowers).
## Footnote
This indicates that the presence of one dominant allele is sufficient to express the dominant trait.
132
Which allele is recessive in Mendel’s flower color experiment?
The allele for white flowers.
## Footnote
Mendel's experiments with pea plants identified the recessive allele responsible for white flowers.
133
What symbols are typically used for dominant and recessive alleles?
Uppercase for dominant (A), lowercase for recessive (a).
## Footnote
This notation helps distinguish between the different types of alleles in genetic representation.
134
What does the genotype Aa represent in Mendel’s peas?
Heterozygous with a purple flower phenotype due to dominance.
## Footnote
This demonstrates how heterozygous genotypes can lead to a dominant phenotype.
135
What does the notation a⁺ or a¹ mean?
Superscripts or subscripts indicate different alleles or wild-type alleles.
## Footnote
This notation is often used in genetic studies to represent variations of a gene.
136
What does the notation A/A mean?
Two alleles on homologous chromosomes at the same locus (i.e., a genotype).
## Footnote
This notation indicates the specific genetic makeup at a given locus.
137
Why is A and a notation not always accurate for all genes?
Not all genes exhibit complete dominance or have only two alleles.
## Footnote
Some genes can have multiple alleles or different patterns of inheritance.
138
In Drosophila, what is the white gene responsible for?
Encoding the WHITE protein on the X chromosome.
## Footnote
This gene is crucial for eye color in fruit flies, demonstrating the role of sex-linked traits.
139
How do you determine dominance in a gene pair?
Through experimental observation—by examining heterozygote phenotypes.
## Footnote
This method allows researchers to identify the dominant trait through observable characteristics.
140
What is the definition of incomplete dominance?
In incomplete dominance, neither allele is completely dominant over the other, resulting in a blending or intermediate phenotype in the heterozygote.
141
In the case of carnation flowers, what are the genotypes for red and white petals?
A₁A₁ (homozygous for red) and A₂A₂ (homozygous for white)
142
What is the phenotype of the heterozygous carnation flower genotype A₁A₂?
Pink petals
143
How does incomplete dominance manifest in the phenotype of heterozygotes?
It results in an intermediate phenotype between both homozygotes.
144
In complete dominance, what is the phenotype of the heterozygote compared to the dominant homozygote?
Same as dominant homozygote
145
Fill in the blank: Incomplete dominance results in a phenotype that is _______ between both homozygotes.
intermediate
146
What does the pink color in A₁A₂ carnation flowers demonstrate about the alleles A₁ and A₂?
Both alleles contribute to the phenotype.
147
What is incomplete dominance?
A genetic condition where neither allele is completely dominant, resulting in a heterozygous phenotype that is intermediate.
## Footnote
Incomplete dominance leads to a blending of traits rather than one trait completely masking another.
148
What is another name for incomplete dominance?
Semi-dominance.
## Footnote
This term is used interchangeably in genetic contexts.
149
What does the heterozygous genotype A₁A₂ produce in carnations?
Pink petals.
## Footnote
This is a result of the blending of the red and white alleles.
150
What phenotype results from A₁A₁ in carnations?
Red petals.
## Footnote
A₁ represents the allele for red color.
151
What phenotype results from A₂A₂ in carnations?
White petals.
## Footnote
A₂ represents the allele for white color.
152
Why are A₁ and A₂ said to show incomplete dominance?
Because neither allele completely masks the other, leading to a blended phenotype in heterozygotes.
## Footnote
This results in intermediate expressions of traits.
153
How does incomplete dominance differ from complete dominance?
In incomplete dominance, the heterozygote shows a blended phenotype; in complete dominance, it matches the dominant homozygote.
## Footnote
Complete dominance results in one phenotype being fully expressed over another.
154
Is pink color in carnations an example of blending inheritance?
No, it is incomplete dominance, not true blending inheritance across generations.
## Footnote
Blending inheritance would imply traits blend in a way that they cannot be separated in future generations.
155
What is Co-Dominance?
In co-dominance, both alleles in a heterozygote are fully and independently expressed.
## Footnote
Unlike in complete dominance, neither allele is masked by the other.
156
What are the three alleles of the ABO gene?
* Iᴬ: Encodes for A antigen on red blood cells
* Iᴮ: Encodes for B antigen
* i: Encodes no antigen
157
What genotype results in Type A blood?
IᴬIᴬ or Iᴬi
## Footnote
A antigen is present.
158
What genotype results in Type B blood?
IᴮIᴮ or Iᴮi
## Footnote
B antigen is present.
159
What genotype results in Type AB blood?
IᴬIᴮ
## Footnote
Both A and B antigens expressed → Co-dominance.
160
What genotype results in Type O blood?
ii
## Footnote
No antigens present; i is recessive.
161
How are Iᴬ and Iᴮ related to each other?
Iᴬ and Iᴮ are co-dominant with respect to each other.
## Footnote
Both are dominant to i.
162
What do people heterozygous IᴬIᴮ show?
Both A and B antigens on their red blood cells.
## Footnote
Not a blend, but a dual expression.
163
True or False: Co-dominance and incomplete dominance are the same.
False
## Footnote
In incomplete dominance, the heterozygote has an intermediate trait, unlike co-dominance where both traits appear fully.
164
What is an example of incomplete dominance?
Pink flowers
## Footnote
In incomplete dominance, the heterozygote has an intermediate trait.
165
In co-dominance, how do the traits appear?
Both traits appear fully and side-by-side.
## Footnote
Example: A and B antigens both showing up.
166
What is co-dominance?
A genetic condition where both alleles in a heterozygote are fully expressed.
167
What is a key feature of co-dominance?
Both alleles produce their effects without blending.
168
Give a human example of co-dominance.
The ABO blood group, specifically blood type AB (IᴬIᴮ).
169
What phenotype does the genotype IᴬIᴮ produce?
Type AB blood (both A and B antigens present).
170
What is the phenotype of a person with genotype ii?
Type O blood (no antigens on red blood cells).
171
Which allele is recessive in the ABO system?
The i allele is recessive to both Iᴬ and Iᴮ.
172
What phenotypes result from Iᴬi and Iᴮi?
* Iᴬi = Type A blood
* Iᴮi = Type B blood.
173
How is co-dominance different from incomplete dominance?
In co-dominance, both traits are fully visible; in incomplete dominance, the traits blend.
174
Are Iᴬ and Iᴮ dominant over each other?
No, they are co-dominant—both are expressed together.
175
What does the ABO blood system show about genetic dominance?
That different types of dominance (co-dominance and complete dominance) can exist at the same gene.
176
What is classical genetics?
The branch of biology that studies inheritance patterns and genetic traits using controlled mating of model organisms.
177
What does classical genetics focus on?
Visible outcomes of genetic crosses, such as phenotype ratios.
178
Who established the foundation of classical genetics and when?
Mendel in 1865.
179
What did Mendel demonstrate?
Traits are inherited as discrete units, now known as genes.
180
What are Mendel's laws of inheritance?
Segregation and independent assortment.
181
Which organism did Thomas Hunt Morgan use to advance classical genetics?
Fruit flies (Drosophila).
182
What did Thomas Hunt Morgan prove?
Genes are located on chromosomes, linking cytology to Mendel's laws.
183
What significant discovery did Watson and Crick make in 1953?
The structure of DNA.
184
What marks the birth of molecular genetics?
The discovery of DNA structure by Watson and Crick.
185
What does molecular genetics study?
Genes at the DNA/RNA/protein level.
186
What tools are used in molecular genetics?
Gene sequencing, PCR, and electrophoresis.
187
When did DNA cloning begin?
In 1970.
188
What discovery allowed the beginning of DNA cloning?
Restriction enzymes.
189
What revolutionized genetics research in the 1970s?
The ability to cut, manipulate, and clone genes.
190
What is the focus of classical genetics?
Phenotypes and inheritance patterns.
191
What is the focus of molecular genetics?
DNA, RNA, and proteins.
192
What is the timeframe for classical genetics?
1865 to the 1950s.
193
What is the timeframe for molecular genetics?
1953 onward.
194
What is the timeframe for DNA cloning genetics?
1970 onward.
195
What is classical genetics?
The study of inheritance using controlled matings and analysis of phenotypes in organisms.
## Footnote
Classical genetics involves understanding how traits are passed from parents to offspring through generations.
196
Who is considered the father of classical genetics?
Gregor Mendel.
## Footnote
Mendel's work with pea plants established foundational principles of heredity.
197
What did Mendel discover in 1865?
That traits are inherited as units (genes), and developed laws of inheritance.
## Footnote
Mendel's findings led to the formulation of the Law of Segregation and the Law of Independent Assortment.
198
What organism did Thomas Hunt Morgan use in classical genetics?
Fruit flies (Drosophila melanogaster).
## Footnote
Morgan's studies provided evidence for the chromosomal theory of inheritance.
199
What major genetic milestone happened in 1953?
Watson and Crick discovered the double helix structure of DNA.
## Footnote
This discovery was crucial for understanding how genetic information is stored and replicated.
200
What is molecular genetics?
The study of biological questions using DNA, RNA, and protein analysis.
## Footnote
Molecular genetics explores the molecular mechanisms behind gene expression and regulation.
201
When did molecular genetics emerge?
After the discovery of DNA structure in 1953.
## Footnote
This period marked a shift toward understanding genetics at the molecular level.
202
What marks the beginning of DNA cloning?
The discovery of restriction enzymes in 1970.
## Footnote
Restriction enzymes allowed scientists to cut and manipulate DNA, paving the way for genetic engineering.
203
What is the role of restriction enzymes?
They cut DNA at specific sequences, enabling gene cloning and manipulation.
## Footnote
This capability is essential for creating recombinant DNA molecules.
204
How are classical and molecular genetics different?
Classical focuses on inheritance patterns; molecular focuses on gene structure and function.
## Footnote
This distinction highlights the evolution of genetic research from phenotypic analysis to molecular understanding.
205
What are true breeding lines?
Populations of organisms where all individuals are homozygous for a specific trait and all offspring show the same phenotype for that trait, generation after generation.
206
Why are true breeding lines important in genetics?
They are predictable and stable, making them ideal for genetic experiments, studying inheritance patterns, and serving as control groups in genetic crosses.
207
What is the result of crossing two true breeding individuals for the same trait?
100% identical homozygous offspring.
208
Who used true breeding lines to discover patterns of inheritance?
Mendel.
209
Fill in the blank: True breeding lines are inbred to ensure _______.
genetic uniformity.
210
Name two modern applications of true breeding lines in research.
* Crops (like maize, rice)
* Lab animals (like mice or fruit flies)
211
What is a true breeding line?
A genetically uniform group of organisms that consistently pass down the same phenotype over generations.
## Footnote
True breeding lines are essential for studying inheritance patterns in genetics.
212
Why are true breeding lines homozygous?
Because both alleles for the trait are identical, ensuring uniform inheritance.
## Footnote
Homozygosity is crucial for maintaining consistency in traits across generations.
213
What happens when two individuals from the same true breeding line are crossed?
All offspring are homozygous and exhibit the same trait.
## Footnote
This predictability is a key aspect of genetic studies.
214
What are true breeding lines also called?
Strains.
## Footnote
The term 'strains' is often used in laboratory settings.
215
Why are true breeding lines useful in genetics?
They allow researchers to study inheritance with consistent and predictable results.
## Footnote
This predictability is vital for experimental design and analysis.
216
Who famously used true breeding lines in genetic experiments?
Gregor Mendel.
## Footnote
Mendel's work with pea plants established foundational principles of inheritance.
217
Can a population be true breeding for multiple traits?
Yes, as long as it is homozygous for each trait being studied.
## Footnote
This allows for complex genetic studies involving multiple characteristics.
218
What ensures that a line remains true breeding?
Repeated self-fertilization or inbreeding to maintain homozygosity.
## Footnote
These methods are used to stabilize genetic traits over generations.
219
What is one major benefit of using true breeding lines in experiments?
It eliminates variability, making it easier to detect the effect of crossing with other genotypes.
## Footnote
This is particularly important in controlled experiments.
220
What type of traits do true breeding lines carry?
Traits that are genetically stable and consistently inherited—usually homozygous traits.
## Footnote
Such traits are crucial for accurate genetic analysis.
221
What is a Monohybrid Cross?
A monohybrid cross examines the inheritance of one single trait
222
What does heterozygous mean in the context of a monohybrid cross?
Heterozygous refers to having two different alleles for a particular gene (Aa)
223
What does P generation stand for?
P generation stands for Parental: Original parents
224
What is the F₁ generation?
F₁ generation is the first set of offspring from the P cross
225
What is the F₂ generation?
F₂ generation is the offspring produced by crossing F₁ individuals
226
In the example of flower color in peas, what are the homozygous parents?
One parent is AA (purple flowers), the other is aa (white flowers)
227
What is the result of the first cross (F₁) between AA and aa?
All offspring = Aa
228
What trait do all F₁ offspring show?
All F₁ offspring show the dominant trait (purple flowers)
229
What is the result of the F₁ self-cross (Aa × Aa)?
1 AA (purple), 2 Aa (purple), 1 aa (white)
230
What is the phenotypic ratio in the F₂ generation from the F₁ self-cross?
3 purple : 1 white
231
Fill in the blank: The P generation consists of _______ parents.
[Original]
232
True or False: In a monohybrid cross, two traits are examined.
False
233
What is a monohybrid cross?
A cross between two individuals heterozygous for a single trait.
## Footnote
This type of genetic cross examines the inheritance of a single trait.
234
What is the genotype of the F₁ generation in a monohybrid cross?
Aa (heterozygous).
## Footnote
The F₁ generation results from the cross of two homozygous parents.
235
What is the phenotypic ratio of the F₂ generation in a monohybrid cross?
3 dominant : 1 recessive.
## Footnote
This ratio reflects the observable traits in the offspring.
236
What do P, F₁, and F₂ stand for?
Parental, First Filial, and Second Filial generations.
## Footnote
These terms describe the different generations in a genetic cross.
237
What is the genotypic ratio in the F₂ generation of a monohybrid cross?
1 AA : 2 Aa : 1 aa.
## Footnote
This ratio indicates the genetic makeup of the F₂ generation.
238
What type of parents are used in a true breeding line?
Homozygous parents (AA or aa).
## Footnote
True breeding lines produce offspring with consistent traits.
239
What kind of trait does a monohybrid cross track?
A single gene trait.
## Footnote
This focuses on one characteristic controlled by a specific gene.
240
Why do all F₁ plants show the dominant phenotype?
Because they carry one dominant allele (A), which masks the recessive one.
## Footnote
Dominance determines the visible traits in the offspring.
241
In a monohybrid cross, when do recessive traits reappear?
In the F₂ generation, when aa genotypes appear.
## Footnote
This occurs due to the segregation of alleles.
242
What law of Mendel does a monohybrid cross illustrate?
Law of Segregation—alleles separate during gamete formation.
## Footnote
This law explains how traits are inherited independently.
243
What is a Punnett Square?
A genetic prediction tool used to determine possible genotypes of offspring from two parents and predict phenotypic ratios based on dominance relationships.
## Footnote
Invented by Reginald Punnett, it is a powerful tool in classical genetics.
244
What are the first steps in using a Punnett Square?
List Parent Gametes: Each parent's gametes are listed along the top and side of a grid.
## Footnote
Example: For heterozygous parents Aa × Aa, each produces gametes A and a.
245
How do you fill in a Punnett Square?
Each box in the grid shows the combination of alleles from the intersecting gametes, modeling fertilization events.
## Footnote
This involves placing the gametes from each parent on the grid.
246
What do you do after filling in the Punnett Square?
Interpret Results: Count the number of each genotype and determine the ratios.
## Footnote
This helps in understanding the genetic outcomes of the offspring.
247
What is the genotypic ratio for Aa × Aa?
1 AA : 2 Aa : 1 aa.
## Footnote
This represents the different genetic combinations possible from the cross.
248
What is the phenotypic ratio if A is dominant in Aa × Aa?
3 Dominant : 1 Recessive.
## Footnote
AA and Aa show the dominant trait, while aa shows the recessive trait.
249
What does each square in a Punnett Square represent in terms of probability?
Each square represents a 25% probability (¼) when both parents produce two types of gametes equally.
## Footnote
This is crucial for calculating the likelihood of various genotypes.
250
How can you calculate offspring frequency using a Punnett Square?
Multiply the frequency of each male gamete by the frequency of each female gamete.
## Footnote
This approach helps predict the distribution of genotypes in the offspring.
251
What is a Punnett square?
A grid used to predict the genotypes and phenotypes of offspring from a genetic cross.
## Footnote
The Punnett square is a fundamental tool in genetics for visualizing the potential genetic outcomes of a cross between two organisms.
252
Who invented the Punnett square?
Reginald Punnett.
## Footnote
Reginald Punnett was a British geneticist known for his work in the field of heredity.
253
What do the rows and columns in a Punnett square represent?
The gametes (sex cells) from each parent.
## Footnote
Each parent contributes one allele for each gene, represented in the rows and columns.
254
What does each box in a Punnett square show?
A possible genotype of the offspring.
## Footnote
Each box represents a combination of alleles from the parents.
255
What are the possible offspring genotypes from an Aa × Aa cross?
AA, Aa, Aa, aa.
## Footnote
This represents the combinations of alleles from the parents.
256
What is the genotypic ratio from Aa × Aa?
1 AA : 2 Aa : 1 aa.
## Footnote
This ratio indicates the relative frequencies of each genotype among the offspring.
257
What is the phenotypic ratio if A is dominant?
3 dominant : 1 recessive.
## Footnote
This phenotypic ratio reflects the observable traits in the offspring.
258
How is the frequency of each offspring calculated?
By multiplying the frequency of the male gamete with the female gamete.
## Footnote
This calculation helps determine the likelihood of each genotype occurring.
259
What kind of inheritance pattern does a Punnett square illustrate best?
Mendelian inheritance for single-gene traits.
## Footnote
Mendelian inheritance describes the inheritance of traits controlled by a single gene.
260
Can Punnett squares be used for multiple traits?
Yes, using dihybrid or multi-hybrid squares, though complexity increases.
## Footnote
These squares allow for the analysis of the inheritance of two or more traits simultaneously.
261
What does Mendel’s First Law (Law of Segregation) state?
Alleles segregate equally into gametes, and each individual inherits one allele from each parent.
262
To which type of genes does Mendel’s First Law apply well?
Autosomal genes (genes on non-sex chromosomes).
263
What are sex-linked genes?
Genes located on the sex chromosomes (X and Y).
264
What is the chromosomal composition of females in humans?
XX
265
What is the chromosomal composition of males in humans?
XY
266
Why do most X-linked loci break Mendel's pattern?
They do not have a counterpart on the Y chromosome.
267
What happens to X and Y chromosomes during meiosis?
They pair up, but they don’t carry the same genes.
268
What is the term for males having only one copy of X-linked genes?
Hemizygous
269
How can a recessive allele on the X chromosome affect males?
It can be expressed even if it would be masked in females.
270
Why is sex-linked inheritance an exception to Mendel’s ratios?
Because the X and Y chromosomes are not fully homologous.
271
What are the standard ratios Mendel's inheritance patterns typically follow?
3:1 or 1:2:1 ratios.
272
What are sex-linked genes?
Genes located on the sex chromosomes (X or Y), especially the X.
## Footnote
Sex-linked genes often influence traits that may be expressed differently in males and females due to their location on the sex chromosomes.
273
Why do sex-linked genes not follow Mendel’s First Law?
Because the X and Y chromosomes are not fully homologous and do not carry the same genes.
## Footnote
This results in different inheritance patterns compared to autosomal genes.
274
What is Mendel’s First Law?
The Law of Equal Segregation: each allele in a pair segregates equally into gametes.
## Footnote
This law applies to autosomal genes where each parent contributes one allele to the offspring.
275
Why do X-linked traits behave differently in males?
Males are hemizygous (only one X chromosome), so any X-linked allele is expressed.
## Footnote
This means that X-linked traits are more likely to be expressed in males than in females.
276
Give an example of an exception to Mendel’s laws.
X-linked inheritance, where genes on the X chromosome don’t pair with those on the Y.
## Footnote
This leads to unique patterns of inheritance that differ from those seen with autosomal traits.
277
What does 'hemizygous' mean?
Having only one copy of a gene, as in X-linked genes in males.
## Footnote
This condition is significant in understanding how certain traits are expressed in males.
278
Do autosomal genes follow Mendel’s rules?
Yes, because both chromosomes have corresponding alleles.
## Footnote
This results in predictable patterns of inheritance as described by Mendel.
279
What happens during meiosis to X and Y chromosomes?
They pair and segregate, but they don’t carry all the same genes.
## Footnote
This unique pairing leads to the specific inheritance patterns seen with sex-linked traits.
280
Can males be carriers of X-linked traits?
No, males either express the trait or do not—no masking occurs with one X.
## Footnote
This is in contrast to females, who can be carriers without expressing the trait.
281
What type of inheritance do X-linked genes follow?
A sex-linked pattern, not standard Mendelian inheritance.
## Footnote
This means that the inheritance of X-linked traits can be traced through family trees differently than autosomal traits.
282
What is the white gene in Drosophila melanogaster?
The white gene (w) is located on the X chromosome
283
What allele corresponds to normal (wild-type) flies in Drosophila?
w⁺
284
What allele causes white eyes in Drosophila?
w
285
What are the eye color results for female Drosophila with genotypes w⁺/w⁺ or w⁺/w?
Red eyes
286
What is the eye color result for female Drosophila with genotype w/w?
White eyes
287
What are the eye color results for male Drosophila with genotype w⁺/Y?
Red eyes
288
What is the eye color result for male Drosophila with genotype w/Y?
White eyes
289
What does hemizygous mean in the context of male Drosophila?
Males carry only one X chromosome, so whatever allele is on it will be expressed
290
What is a reciprocal cross?
A cross where the sex of the parents carrying each allele is swapped to see if offspring results change
291
What is the outcome of the first cross: ♀ w⁺/w⁺ × ♂ w/Y?
All F₁ = red-eyed females and white-eyed males
292
What is the outcome of the reciprocal cross: ♀ w/w × ♂ w⁺/Y?
All F₁ = red-eyed females and red-eyed males
293
What conclusion can be drawn if reciprocal crosses give different F₁/F₂ results?
The gene is likely sex-linked
294
Who was Thomas Hunt Morgan?
A scientist who used reciprocal crosses to prove that genes are carried on chromosomes
295
What prestigious award did Thomas Hunt Morgan win for his discovery?
Nobel Prize
296
What is the sex chromosome system in humans and many animals?
XX/XY system
297
What is the sex chromosome system in birds?
ZZ (male) and ZW (female)
298
True or False: The pattern of sex-linked inheritance is the same in birds as in Drosophila.
True
299
What are the mechanisms animals use to determine an individual's sex?
Animals use the following mechanisms:
* Sex chromosomes
* Chromosome dosage (ratio)
* Environmental cues
## Footnote
These systems vary widely among different species.
300
What is the XX-XY system?
Common in humans and most mammals where XY = male and XX = female
## Footnote
The key determinant is the TDF-Y gene on the Y chromosome.
301
What does the presence of the TDF-Y gene indicate?
If present, the embryo develops male features; if absent, the embryo becomes female
## Footnote
Only one gene (TDF-Y) triggers male development.
302
What is the X:A ratio system?
Used in fruit flies where the sex is determined by the ratio of X chromosomes to autosomes:
* 2X:2A (1.0) → Female
* 1X:2A (0.5) → Male
## Footnote
The Y chromosome is not essential for sex determination in flies.
303
What does a 2X:2A ratio indicate in Drosophila melanogaster?
It indicates a female
## Footnote
This ratio is 1.0.
304
What does a 1X:2A ratio indicate in Drosophila melanogaster?
It indicates a male
## Footnote
This ratio is 0.5.
305
What is the haploid-diploid system?
Used by bees, ants, and wasps where haploid (1 set of chromosomes) → Male and diploid (2 sets) → Female
## Footnote
Males develop from unfertilized eggs, females from fertilized eggs.
306
How do environmental conditions affect sex determination?
Sex can depend on external conditions, such as temperature or population density
## Footnote
Examples include alligators and reef fish.
307
What determines the sex of alligator embryos?
Temperature during egg incubation
## Footnote
This is a form of environmental sex determination.
308
Can some reef fish change sex?
Yes, based on the local population's sex ratio
## Footnote
This adaptation helps maintain reproductive balance.
309
What are the three main categories of sex determination in animals?
Sex chromosomes, chromosome dosage, and environmental cues.
310
What determines sex in humans?
Presence of the TDF-Y gene on the Y chromosome.
311
What sex chromosomes do human males and females have?
Males = XY, Females = XX.
312
What sex determination system does Drosophila melanogaster use?
X:A ratio system.
313
In fruit flies, what X:A ratio produces a female?
2X:2A (or 1.0 ratio).
314
In fruit flies, what X:A ratio produces a male?
1X:2A (or 0.5 ratio).
315
What is the haploid-diploid system?
A system where haploid individuals become males and diploid individuals become females (e.g., in bees and ants).
316
How do male bees develop?
From unfertilized (haploid) eggs.
317
Give an example of environmental sex determination.
In alligators, temperature during egg incubation determines sex.
318
Can some animals change sex during their lifetime?
Yes—reef fish can change sex in response to population sex ratios.
319
What is the dosage problem in XX-XY sex determination systems?
Females have double the amount of X-linked gene products compared to males if no correction is made.
## Footnote
This imbalance can lead to toxic imbalances in protein production between males and females.
320
What are the X chromosome configurations in females and males in XX-XY systems?
Females have two X chromosomes (XX) and males have one X chromosome (XY).
## Footnote
This configuration is typical in species like mammals and Drosophila.
321
Why do XY males have half the gene dosage of XX females for X-linked genes?
The Y chromosome lost most of its genes over time, leading to this imbalance.
## Footnote
This process is referred to as degeneration.
322
What is the purpose of dosage compensation mechanisms?
To equalize X-linked gene expression between the sexes.
## Footnote
This prevents toxic imbalances in gene expression.
323
How do dosage compensation mechanisms work in Drosophila?
Males upregulate their single X chromosome, expressing genes at 2× the normal rate.
## Footnote
This restores balance between X-linked and autosomal gene expression.
324
What is X-chromosome inactivation (XCI) in mammals?
One of the two X chromosomes in females is inactivated.
## Footnote
This process is also known as Lyonization.
325
What effect does X-chromosome inactivation have on female cells?
Makes female cells functionally equivalent to XY males, with one active X chromosome.
## Footnote
This helps maintain balance in gene expression between sexes.
326
What is the solution for the dosage problem in Drosophila?
X-linked genes are expressed at 2× the rate in males.
## Footnote
This compensatory mechanism effectively balances gene expression.
327
What is the solution for the dosage problem in mammals?
One X chromosome is inactivated in females.
## Footnote
This ensures that females have a similar gene dosage to males.
328
Fill in the blank: In Drosophila, males have only 1 X chromosome, and the solution is that X-linked genes are expressed at _______.
2× rate
329
Fill in the blank: In mammals, females have 2 X chromosomes, and the solution is that one X is _______.
inactivated (XCI)
330
What is dosage compensation?
The process of equalizing X-linked gene expression between males and females.
331
Why is dosage compensation necessary in XX-XY systems?
Because females have two X chromosomes and males only one, leading to potential gene dosage imbalances.
332
What is the state of the Y chromosome in modern mammals?
It has lost most of its genes due to degeneration.
333
What dosage compensation method is used in Drosophila?
Males express genes on their single X chromosome at twice the normal rate.
334
What dosage compensation method is used in mammals?
X-chromosome inactivation in females.
335
What does X-chromosome inactivation do?
Silences one X chromosome in each female cell to equalize gene expression with males.
336
What’s the effect of not compensating for gene dosage?
Imbalanced protein production, which can disrupt cellular and organismal function.
337
Are autosomal genes affected by dosage compensation?
No, dosage compensation specifically targets X-linked genes.
338
In Drosophila, why don’t females need dosage compensation?
Because males adjust by upregulating their single X, not downregulating the female’s Xs.
339
What is another term for X-chromosome inactivation?
Lyonization.
340
What is the purpose of X-chromosome inactivation (XCI) in mammals?
To ensure equal dosage of X-linked genes between sexes
## Footnote
XCI is a form of dosage compensation that occurs in female mammals.
341
How many X chromosomes do females and males have in mammals?
Females have two X chromosomes (XX), males have one (XY)
## Footnote
This difference necessitates a mechanism to balance gene expression.
342
What happens to one X chromosome in each female cell?
One X chromosome is randomly inactivated
## Footnote
This process occurs early in embryonic development.
343
What are the designations for the inactive and active X chromosomes?
Inactive X = Xᵢ (X-inactive), Active X = Xₐ (X-active)
## Footnote
Xᵢ is silenced, while Xₐ remains functional.
344
What is a Barr body?
The condensed, visible structure of the inactive X chromosome in the nucleus
## Footnote
The Barr body is replicated in cell division but remains inactive.
345
What is the result of X-chromosome inactivation in female mammals?
They have one functional X chromosome per cell
## Footnote
This ensures balanced gene expression similar to males.
346
What does the O gene control in cats?
Fur color
## Footnote
The O gene is X-linked.
347
What are the alleles for the O gene in cats?
* Oᴼ allele: Orange pigment
* Oᴮ allele: Black pigment
## Footnote
These alleles determine the fur color phenotype.
348
What are the genotypes and corresponding phenotypes for the O gene in cats?
* OᴼOᴼ: Orange female
* OᴮOᴮ: Black female
* OᴼOᴮ: Tortoiseshell
* OᴼY: Orange male
* OᴮY: Black male
## Footnote
Tortoiseshell cats exhibit a mix of orange and black fur due to XCI.
349
How does X-chromosome inactivation cause mosaic expression in OᴼOᴮ females?
In some cells, the Oᴼ allele is active, in others, the Oᴮ allele is active
## Footnote
This leads to mottled fur patterns commonly seen in tortoiseshell cats.
350
What is X-chromosome inactivation (XCI)?
The random silencing of one X chromosome in each female cell to balance gene expression with males.
## Footnote
XCI is a mechanism to equalize gene dosage between males and females.
351
What are the two types of X chromosomes after inactivation?
Xᵢ (inactive) and Xₐ (active).
## Footnote
These designations help in understanding gene expression levels in female cells.
352
What structure does the inactivated X form in the nucleus?
Barr body.
## Footnote
The Barr body is a condensed and transcriptionally inactive X chromosome.
353
Does XCI occur in males?
No, it occurs only in females (XX), since males (XY) already have one X.
## Footnote
Males do not require XCI as they have only one X chromosome.
354
When does XCI occur?
Early during embryonic development.
## Footnote
This timing is crucial for proper dosage compensation.
355
Why do tortoiseshell cats have patches of color?
Due to random X-inactivation of either the Oᴼ or Oᴮ allele in different skin cells.
## Footnote
This results in a mosaic pattern of color in the fur.
356
Which X-linked gene affects fur color in cats?
The Orange gene (O).
## Footnote
The expression of this gene determines the color patterns seen in cats.
357
What phenotype results from an OᴼOᴮ genotype?
Tortoiseshell (mottled orange and black).
## Footnote
This phenotype is a direct result of X-inactivation patterns.
358
What determines which X chromosome is inactivated in a cell?
It is random in each cell of the early embryo.
## Footnote
This randomness contributes to the diversity of phenotypes in females.
359
What is the purpose of XCI?
To ensure dosage compensation so that females don't express twice as many X-linked gene products as males.
## Footnote
This mechanism is vital for maintaining balance in gene expression.
360
What type of inheritance does the Orange gene in cats exhibit?
X-linked inheritance
## Footnote
The Orange gene affects fur color in cats.
361
What is the allele for orange pigment in cats?
Oᴼ allele
## Footnote
This allele corresponds to the orange color in the fur.
362
What is the allele for black pigment in cats?
Oᴮ allele
## Footnote
This allele corresponds to the black color in the fur.
363
What phenotype do OᴼOᴼ genotype female cats exhibit?
Orange female
## Footnote
This represents a female with two orange alleles.
364
What phenotype do OᴮOᴮ genotype female cats exhibit?
Black female
## Footnote
This represents a female with two black alleles.
365
What phenotype do OᴼOᴮ genotype female cats exhibit?
Tortoiseshell
## Footnote
This phenotype has both orange and black patches.
366
What is the male phenotype for the OᴼY genotype in cats?
Orange male
## Footnote
This represents a male with one orange allele.
367
What is the male phenotype for the OᴮY genotype in cats?
Black male
## Footnote
This represents a male with one black allele.
368
Why are tortoiseshell females patchy?
Due to X-chromosome inactivation (XCI)
## Footnote
Different X chromosomes are inactivated in different skin cells.
369
What is the F8 gene responsible for in humans?
Encoding Factor VIII
## Footnote
Factor VIII is a blood-clotting protein made in liver cells.
370
What disorder is caused by a mutation in the F8 gene?
Hemophilia A
## Footnote
Hemophilia A is a bleeding disorder.
371
What genotype corresponds to a male with hemophilia?
F8⁻/Y
## Footnote
This genotype indicates the presence of the mutated F8 allele.
372
What genotype corresponds to a female with hemophilia?
F8⁻/F8⁻
## Footnote
This genotype indicates both alleles are mutated.
373
What genotype corresponds to a female who is a carrier of hemophilia?
F8⁺/F8⁻
## Footnote
This female has one normal and one mutated allele.
374
What genotype corresponds to a female without hemophilia?
F8⁺/F8⁺
## Footnote
This female has two normal alleles.
375
Why are F8⁺/F8⁻ females not affected by hemophilia?
Due to random XCI
## Footnote
Half of liver cells inactivate the F8⁺ allele, allowing enough Factor VIII production.
376
What is the outcome of partial production of Factor VIII in F8⁺/F8⁻ females?
Prevention of hemophilia
## Footnote
Even partial levels of Factor VIII are sufficient to prevent the disorder.
377
What is the difference between visible and silent mosaicism?
Visible mosaicism affects physical traits; silent mosaicism affects internal processes without changing outward phenotype
## Footnote
In cats, mosaicism is visible in fur color; in humans, it may not be visible.
378
What does the Oᴼ allele do in cats?
Produces orange pigment in fur.
379
What is the phenotype of a cat with OᴼOᴮ genotype?
Tortoiseshell (patches of orange and black fur).
380
Why do tortoiseshell cats exist only in females?
Because X-inactivation causes different X alleles to be expressed in different cells.
381
What does the F8 gene do in humans?
It produces Factor VIII, a blood-clotting protein.
382
What is the phenotype of a male with an F8⁻ mutation?
Hemophilia A (cannot clot blood properly).
383
What is the phenotype of a heterozygous female (F8⁺/F8⁻)?
Normal—enough Factor VIII is produced due to X-inactivation mosaicism.
384
Why don’t F8⁺/F8⁻ females have hemophilia?
Because the active X chromosome in half the liver cells produces sufficient Factor VIII.
385
What term describes the patchy expression of traits due to X-inactivation?
Genetic mosaicism.
386
Is X-linked mosaicism always visible?
No—only visible in traits like coat color; not in internal traits like clotting factors.
387
What makes the F8⁻ mutation recessive in females?
One functional F8⁺ allele is enough to maintain normal function due to secreted protein.
388
What is a Z-linked gene?
Z-linked genes are located on the Z chromosome in species with a ZZ-ZW sex determination system.
## Footnote
This system is found in birds, such as turkeys.
389
What are the male and female genotypes in the ZZ-ZW sex determination system?
Males = ZZ; Females = ZW.
## Footnote
Males have two Z chromosomes, while females have one Z and one W chromosome.
390
What does the E allele produce in turkeys?
The E allele produces bronze feathers.
## Footnote
The e allele produces brown feathers.
391
What is the dominance relationship between the E and e alleles?
The E allele is dominant over e.
## Footnote
This dominance affects the feather color in turkeys.
392
What are the possible genotypes for male turkeys (ZZ)?
E/E, E/e, or e/e.
## Footnote
These genotypes determine the feather color.
393
What feather color does the genotype E/E produce in male turkeys?
Bronze.
## Footnote
E/e also results in bronze due to the dominance of E.
394
What feather color does the genotype e/e produce in male turkeys?
Brown.
## Footnote
This is the result when only the recessive allele is present.
395
What are the possible genotypes for female turkeys (ZW)?
E/W or e/W.
## Footnote
Females express only one allele at the locus.
396
What feather color does the genotype E/W produce in female turkeys?
Bronze.
## Footnote
Only the E allele is expressed.
397
What feather color does the genotype e/W produce in female turkeys?
Brown.
## Footnote
Only the e allele is expressed.
398
How is Z-linked inheritance similar to X-linked inheritance in mammals?
It is similar in that males are homogametic (ZZ) and females are heterogametic (ZW).
## Footnote
However, the chromosome roles are reversed.
399
How do we know if a gene is Z-linked?
Reciprocal crosses reveal Z-linkage.
## Footnote
If phenotypic results differ based on which sex carries which allele, the gene is sex-linked.
400
What is dosage compensation in birds?
Birds use a dosage compensation system similar to Drosophila, where males upregulate gene expression to match levels across sexes.
## Footnote
This ensures balanced gene expression despite different sex chromosome compositions.
401
What is the sex chromosome system in birds?
ZZ-ZW, where males are ZZ and females are ZW.
402
What chromosome carries Z-linked genes?
The Z chromosome.
403
What does the E allele do in turkeys?
Produces bronze feathers.
404
What phenotype does the e allele produce?
Brown feathers.
405
What is the phenotype of an E/e male turkey?
Bronze, because E is dominant.
406
What is the phenotype of an e/W female turkey?
Brown, because only e is present.
407
Can female turkeys be heterozygous for Z-linked genes?
No, because they have only one Z chromosome.
408
How does dosage compensation work in birds?
Like in Drosophila—males upregulate Z-linked genes to match expression across sexes.
409
How do scientists confirm if a gene is Z-linked?
By performing reciprocal crosses and comparing offspring phenotypes.
410
Why do only male turkeys show heterozygosity for Z-linked traits?
Because males are ZZ and females are ZW, so only males have two Z chromosomes.
411
What is sex determination?
Sex is a phenotype, determined by genetic or environmental factors
## Footnote
Examples include traits like eye color or height
412
What are hermaphrodites?
Individuals that have both male and female reproductive organs
413
What are the two key mechanisms by which sex is expressed?
* Hormonal
* Cell-autonomous
414
What is the hormonal mechanism of sex determination?
A signal like TDF-Y initiates hormonal cascades for male or female development
## Footnote
Seen in humans
415
What is the cell-autonomous mechanism of sex determination?
Each cell autonomously decides its sex fate based on internal signals or gene dosage
## Footnote
Seen in species like Drosophila, chickens, grasshoppers, and bees
416
What is the XX/XY system of genetic sex determination?
Humans and mammals with male genotype XY and female genotype XX
## Footnote
TDF-Y triggers male development
417
What is the ZZ/ZW system of genetic sex determination?
Birds, moths, and butterflies with male genotype ZZ and female genotype ZW
## Footnote
Female is heterogametic
418
What is the XX/XO system of genetic sex determination?
Grasshoppers with male genotype XO and female genotype XX
## Footnote
No Y chromosome in males
419
What is the haplo-diploid system of genetic sex determination?
Bees, ants, and wasps with males being haploid and females being diploid
## Footnote
Males develop from unfertilized eggs
420
What is environmental sex determination?
Common mechanism where environmental factors like temperature influence sex determination
## Footnote
Example seen in reptiles
421
What is parthenogenesis?
Asexual reproduction where females produce offspring without fertilization
422
Fill in the blank: The male genotype in the XX/XY system is _____
XY
423
True or False: In the ZZ/ZW system, males are heterogametic.
False
424
Fill in the blank: In the XX/XO system, males have the genotype _____
XO
425
What visual examples are shown in the summary image?
* XX/XY (humans)
* ZZ/ZW (chickens)
* XX/XO (grasshoppers)
* Diploid/Haploid (bees)
426
Is sex a genotype or phenotype?
Phenotype—it is the observable physical outcome of genetic or environmental input.
## Footnote
Phenotype refers to the expression of traits, while genotype refers to the genetic makeup.
427
What is a hermaphrodite?
An organism that possesses both male and female sex organs.
## Footnote
Hermaphroditism can be found in various species, including some plants and animals.
428
What are the two mechanisms cells use to determine sex?
Hormonal and cell-autonomous.
## Footnote
Hormonal mechanisms involve hormones influencing sex development, while cell-autonomous mechanisms rely on the cell's own genetic information.
429
What sex determination system do humans use?
XX/XY, with TDF-Y triggering male development.
## Footnote
TDF-Y stands for Testis Determining Factor on the Y chromosome, crucial for male sex determination.
430
What chromosome system is used by birds?
ZZ/ZW—males are ZZ and females are ZW.
## Footnote
This system is different from the XY system seen in mammals.
431
In the XX/XO system, who lacks a second sex chromosome?
Males (XO), as seen in grasshoppers.
## Footnote
In this system, females are XX, while males have only one X chromosome.
432
What species use the haploid-diploid system?
Bees, ants, and wasps.
## Footnote
In this system, fertilization determines the sex of the offspring.
433
In the haploid-diploid system, how do males and females arise?
Males from unfertilized haploid eggs; females from fertilized diploid eggs.
## Footnote
This reproductive strategy leads to males being haploid and females diploid.
434
What does the ZW system have in common with the XY system?
Both have one sex being heterogametic (XY or ZW).
## Footnote
Heterogametic means having two different sex chromosomes.
435
Which system uses a hormonal mechanism for sex determination?
Humans (XX/XY).
## Footnote
Hormonal mechanisms in humans involve sex hormones influencing sexual development.
436
What is the hormonal mechanism of sex expression?
Common in humans and mammals.
## Footnote
Initially, the embryo is sexually undifferentiated, and genital ridge cells differentiate into testes or ovaries based on genotype.
437
How do gonads influence sexual development in the hormonal mechanism?
They produce hormones (like testosterone or estrogen) that circulate and influence development of the body.
## Footnote
Hormones effectively “tell” all cells of the body which sex to express.
438
What is a freemartin?
A female twin of a male calf that is infertile and masculinized.
## Footnote
During development, hormones from the male twin affect the female twin, suppressing normal ovarian development.
439
What happens during the development of a freemartin?
Cells or hormones from the male twin cross into the female twin via shared placental blood vessels.
## Footnote
This results in the female twin receiving male hormones.
440
What is the cell-autonomous mechanism of sex expression?
Each individual cell autonomously knows its sex without a central hormonal signal.
## Footnote
Sex is determined by internal gene dosage or chromosomal content.
441
How do cells determine their sex in the cell-autonomous mechanism?
Cells express either male or female phenotypes on their own.
## Footnote
There is no external hormonal influence directing sex development.
442
What are sexual gynandromorphs?
Organisms with some cells having male chromosomes and others having female chromosomes.
## Footnote
This leads to mosaic sex expression, often split down the middle.
443
In which organisms are sexual gynandromorphs commonly found?
Common in insects like Drosophila and butterflies.
## Footnote
They are easily visible in sexually dimorphic species.
444
Describe the appearance of a gynandromorph fruit fly.
Left side = female: less pigmented; Right side = male: more pigmented.
## Footnote
This is due to X chromosome mis-segregation during early cell divisions.
445
True or False: In the hormonal mechanism, the embryo starts as sexually differentiated.
False.
## Footnote
The embryo is initially sexually undifferentiated.
446
Fill in the blank: In the hormonal mechanism, the gonads influence the development of the rest of the body by producing _______.
[hormones].
## Footnote
Hormones like testosterone or estrogen play a crucial role in sexual differentiation.
447
What is the hormonal mechanism of sex determination?
A system where hormones produced by the gonads instruct all body tissues to develop as male or female
## Footnote
This mechanism is prevalent in mammals, including humans.
448
What is the cell-autonomous mechanism of sex determination?
A system where each cell determines its own sex phenotype independently
## Footnote
This is commonly found in birds, insects, and many invertebrates.
449
What organism typically uses hormonal sex determination?
Mammals, including humans
450
What types of organisms typically use cell-autonomous sex determination?
Birds, insects, and many invertebrates
451
What is a freemartin?
A sterile female twin of a male calf, affected by male hormones via shared placenta
452
What causes freemartinism in cattle?
Hormonal interference from a male twin while in utero
453
What is a gynandromorph?
An individual with both male and female body parts due to chromosomal mosaicism
454
How do gynandromorphs form?
Through mitotic errors or sex chromosome segregation mistakes early in development
455
Why are gynandromorphs visible in species like fruit flies?
Because they are sexually dimorphic, so male and female parts look different
456
Which mechanism uses internal chromosomal signals to determine sex at the cellular level?
Cell-autonomous mechanism
457
What are gynandromorphs?
An organism that contains a mixture of male and female cells and displays both male and female characteristics.
## Footnote
Only possible in cell-autonomous species where individual cells determine their sex.
458
In which species are gynandromorphs found?
Cell-autonomous species such as birds and insects like butterflies and fruit flies.
## Footnote
Not found in mammals or other hormonally regulated species.
459
Why are gynandromorphs not found in mammals?
Hormones dictate sex in mammals, causing all cells to respond uniformly to the same hormonal signals.
## Footnote
Even if a mutation causes variation at the cellular level, sex traits remain uniform across the organism.
460
Do reptiles, amphibians, and fish have gynandromorphs?
No strong evidence suggests they do.
## Footnote
They likely use non-cell-autonomous (hormonal or environmental) mechanisms.
461
What is genetic mosaicism?
A condition where some individuals show genetic mosaics involving non-sex traits.
## Footnote
Example: Mosaic fur color resulting from allelic variation at single genes.
462
What is a mosaic?
An individual or tissue composed of two or more cell populations with different genotypes.
## Footnote
All cells come from the same zygote.
463
What is a chimera?
An organism formed by the fusion of two or more zygotes, each contributing genetically distinct cells.
## Footnote
Can happen in mammals and plants.
464
Fill in the blank: Gynandromorphs are only possible in _______ species.
cell-autonomous
465
True or False: Gynandromorphs can occur in mammals.
False
466
Fill in the blank: A genetic mosaic typically involves _______ traits.
non-sex
467
What is a gynandromorph?
An organism with both male and female tissues caused by sex chromosome mosaicism.
## Footnote
Gynandromorphs exhibit a unique combination of male and female characteristics due to genetic variations in their cells.
468
Why are gynandromorphs not found in mammals?
Because mammals use hormonal sex determination, which causes all cells to respond uniformly.
## Footnote
This uniform response prevents the development of mixed-sex characteristics in mammals.
469
What type of species can produce gynandromorphs?
Cell-autonomous species like insects and birds.
## Footnote
These species allow for independent cell-level sex determination, leading to gynandromorphism.
470
What is a mosaic organism?
One that has two or more genetically different cell types from the same zygote.
## Footnote
Mosaics can occur in various forms, affecting traits and characteristics in an organism.
471
What is a chimera?
An organism made of genetically distinct cells that originated from different zygotes.
## Footnote
Chimeras are distinct from mosaics as they involve cells from separate embryos.
472
How do chimeras typically form?
Through fusion of embryos or cell transfer early in development (e.g., twin calves sharing cells).
## Footnote
This process can lead to unique physiological traits in the resulting organism.
473
Can genetic mosaics show visible traits?
Yes, but in mammals they usually affect traits like color, not sex.
## Footnote
Visible traits in mosaics may not always be indicative of sex differentiation.
474
Do reptiles or amphibians show gynandromorphism?
No evidence supports that—they likely do not use a cell-autonomous mechanism.
## Footnote
The absence of gynandromorphism in these groups suggests different mechanisms of sex determination.
475
What is needed for an organism to be a true gynandromorph?
Cell-autonomous sex determination and sex chromosome mosaicism.
## Footnote
These conditions create the necessary environment for the development of gynandromorphic traits.
476
What makes gynandromorphs visibly unique?
They often show a mosaic pattern split along the body, with male traits on one side and female traits on the other.
## Footnote
This distinctive appearance is a key characteristic of gynandromorphs.
477
What is the relationship between genotype and phenotype?
There is often a strong correlation between an individual's genotype (G) and their phenotype (P), but it is not always the complete picture.
478
Define phenotype.
Phenotype refers to the observable traits of an individual.
479
What are the three components that shape phenotype?
* Genotype (G) - inherited DNA
* Environment (E) - external influences
* G × E Interaction (I_GE) - how genes and environment affect each other
480
What does the basic model of phenotype determination include?
Genotype + Environment ⇒ Phenotype (G + E ⇒ P)
481
What does the full model of phenotype determination include?
Genotype + Environment + Interaction ⇒ Phenotype (G + E + I_GE ⇒ P)
482
What is the significance of G × E interaction?
It indicates that the effect of the environment depends on the genotype, and vice versa.
483
Provide an example of how phenotype is influenced by genotype and environment.
A person may have a genetic predisposition to cancer (e.g., BRCA1 mutation) but might not develop cancer without environmental triggers.
484
List some environmental triggers that can affect cancer susceptibility.
* Radiation
* Smoking
* DNA-damaging chemicals
485
True or False: All people with the same genotype show the same phenotype.
False
486
Why is understanding G + E + I_GE important in agriculture and medicine?
* Improves crop productivity
* Enhances disease risk assessment
* Supports precision medicine
487
Fill in the blank: Phenotype is shaped by the interaction of genotype, environment, and _______.
G × E Interaction (I_GE)
488
What does G + E → P mean?
Phenotype is determined by both genotype and environment.
## Footnote
G stands for genotype, E for environment, and P for phenotype.
489
What does G + E + I_GE → P represent?
Phenotype is influenced by genotype, environment, and their interaction.
## Footnote
I_GE stands for the interaction between genotype and environment.
490
What is I_GE?
The interaction between genetics and environment that influences phenotype.
491
Why is phenotype not always predictable from genotype alone?
Because environmental factors can influence gene expression or effects.
492
Give an example of a gene-environment interaction.
A cancer gene may only lead to disease if exposed to harmful chemicals.
493
How does this concept apply in agriculture?
Crop yield may depend on both genetic traits and environmental conditions (e.g. drought).
494
Why might two people with the same gene mutation have different outcomes?
Due to differences in their environmental exposures.
495
Can environmental effects be independent of genotype?
Yes, but their impact often depends on the genotype.
496
Is G → P always true?
Not always—environment and interaction must be considered.
497
What is one benefit of recognizing G + E + I_GE effects?
More accurate predictions of disease risk and trait performance.
498
What is penetrance?
The proportion of individuals with a particular genotype who actually express the expected phenotype.
## Footnote
Usually given as a percentage.
499
What indicates complete penetrance?
100% of individuals with the genotype express the trait.
## Footnote
Example: In pea plants, genotype aa produces white flowers, and all plants with aa have white flowers.
500
What is incomplete penetrance?
Less than 100% of individuals with the genotype show the trait.
## Footnote
Human diseases often show incomplete penetrance.
501
What is expressivity?
The degree or severity to which a genotype is expressed in an individual.
## Footnote
Can be narrow (constant) or broad (variable).
502
What does narrow expressivity mean?
All affected individuals show the same level of trait expression.
503
What does broad expressivity mean?
Some individuals show mild symptoms, while others show severe symptoms, even with the same genotype.
504
What is an example of expressivity?
Two people with the same genetic disorder might show symptoms, but one could have mild issues and the other severe problems.
505
What does complete penetrance and narrow expressivity look like in a visualization summary?
All black phenotype with all showing mutant phenotype with the same severity.
506
What does complete penetrance and broad expressivity look like in a visualization summary?
Varying black shades phenotype with all showing phenotype, but severity varies.
507
What does incomplete penetrance and narrow expressivity look like in a visualization summary?
Some white, some black phenotype with some showing phenotype, those who do are identical.
508
What does incomplete penetrance and broad expressivity look like in a visualization summary?
Some white, some different black shades phenotype with some showing phenotype, and severity varies among them.
509
Why are penetrance and expressivity important?
They explain why two people with the same disease gene may show different symptoms.
510
What factors can influence penetrance and expressivity?
Chance, environmental influences, modifiers in other genes.
511
What is penetrance?
The proportion of individuals with a specific genotype who express the expected phenotype.
## Footnote
Penetrance can be complete or incomplete based on whether the phenotype is expressed in all individuals with the genotype.
512
What is complete penetrance?
When 100% of individuals with the genotype show the phenotype.
## Footnote
This indicates that the genotype consistently leads to the expected phenotype.
513
What is incomplete penetrance?
When fewer than 100% of individuals with the genotype show the phenotype.
## Footnote
This suggests that some individuals with the genotype do not express the expected phenotype.
514
What is expressivity?
The degree to which a phenotype is expressed in individuals with the same genotype.
## Footnote
Expressivity can vary significantly even among individuals with the same genetic makeup.
515
What is narrow expressivity?
All affected individuals show the trait to the same extent.
## Footnote
This results in a uniform expression of the phenotype across individuals.
516
What is broad expressivity?
Affected individuals show the trait to varying degrees.
## Footnote
This indicates a range of phenotypic expressions among individuals with the same genotype.
517
Can a trait be incompletely penetrant but have broad expressivity?
Yes, some individuals may not show the trait at all, and those who do may show it to different extents.
## Footnote
This highlights the complexity of genetic expression in a population.
518
What causes variation in penetrance and expressivity?
Genetic background, environment, random factors, and modifier genes.
## Footnote
These factors can influence how a genotype translates into a phenotype.
519
Is penetrance qualitative or quantitative?
Qualitative—present or absent.
## Footnote
This classification indicates whether the phenotype is expressed at all.
520
Is expressivity qualitative or quantitative?
Quantitative—how much of the trait is expressed.
## Footnote
This classification measures the level or intensity of the phenotype expression.
521
What are phenotypic ratios?
Expected distribution of physical traits (phenotypes) in offspring based on Mendelian genetics
## Footnote
Predictions like Punnett Squares are used to determine these ratios.
522
What is the phenotypic ratio predicted by a monohybrid cross Aa × Aa?
3:1 dominant:recessive ratio
## Footnote
This ratio represents the expected distribution of dominant and recessive traits.
523
Why do real phenotypic ratios often differ from expected ratios?
Several reasons including sampling effects and reduced survival or viability
## Footnote
These factors can lead to discrepancies between observed and expected results.
524
What are sampling effects in the context of phenotypic ratios?
Results can be skewed if the sample size is small or not representative
## Footnote
Chance can lead to deviation from the expected ratio.
525
Provide an example of a sampling effect.
Flipping a coin 10 times may not give exactly 5 heads and 5 tails
## Footnote
This illustrates randomness affecting outcomes.
526
What is reduced survival or viability in genetics?
Some genotypes may cause early death or reduced survival
## Footnote
These genotypes might not appear in the observed population.
527
What is an example related to Drosophila and reduced viability?
Zygotes with multiple mutant alleles may die early and are not counted in adult fly counts
## Footnote
This leads to underrepresentation of those genotypes in data.
528
What is the purpose of the chi-square (χ²) test?
To assess whether the difference between observed and expected results is due to random chance or another factor
## Footnote
It helps geneticists determine the fit of observed results to predictions.
529
What does a low χ² value indicate?
Differences are likely due to chance
## Footnote
This suggests that the observed results align closely with expected results.
530
What does a high χ² value suggest?
Results are statistically significant, indicating real biological causes for deviation
## Footnote
This suggests factors beyond random chance are influencing the results.
531
Why might phenotypic ratios not match predictions?
Due to sampling effects or biological causes like reduced genotype survival.
## Footnote
Sampling effects can lead to discrepancies between observed and expected ratios due to random chance.
532
What are sampling effects?
Random chance leading to deviations when sample size is small or unbalanced.
## Footnote
Smaller sample sizes can lead to greater variability in observed outcomes.
533
How does reduced survival impact phenotypic ratios?
Some genotypes may die before observation, skewing the expected outcome.
## Footnote
This can occur due to environmental factors or genetic disadvantages.
534
What example organism is used to show survival-based deviations?
Drosophila (fruit flies).
## Footnote
Drosophila is commonly used in genetic studies due to its short life cycle and well-understood genetics.
535
What is the purpose of a chi-square (χ²) test in genetics?
To determine if the difference between observed and expected ratios is due to chance.
## Footnote
This statistical test helps assess the goodness of fit between observed data and expected outcomes.
536
What does a high χ² value suggest?
That observed deviations are likely due to a biological or experimental factor, not just chance.
## Footnote
A high value indicates a significant discrepancy from the expected ratios.
537
What does a low χ² value suggest?
That the observed differences are probably due to random variation.
## Footnote
A low value indicates that the observed data fits the expected model well.
538
What are expected ratios usually based on?
Mendelian genetics and Punnett Square predictions.
## Footnote
These ratios are derived from fundamental principles of inheritance established by Gregor Mendel.
539
Why is it important to use statistical tests in genetics?
To avoid falsely interpreting random variation as significant deviation.
## Footnote
Statistical tests provide a framework for evaluating the validity of observed data.
540
What happens if genotypes with lethal mutations are included in predictions but not observed?
The observed phenotypic ratio will deviate significantly from the expected.
## Footnote
Lethal mutations can prevent certain genotypes from being represented in the offspring.
541
What is the maximum number of alleles for a given locus in a normal gamete of a diploid species?
One allele per locus
## Footnote
Each gamete contains only one allele per gene locus because gametes are haploid (n), formed through meiosis where homologous chromosomes (and thus alleles) are separated.
542
What is the genotype and phenotype result of the cross WW × ww in wire-haired dogs?
Genotype: All Ww (heterozygous)
Phenotype: All wire-haired 🐶
543
What are the genotypic and phenotypic ratios for the cross Ww × Ww in wire-haired dogs?
Genotypic ratio: 1 WW : 2 Ww : 1 ww
Phenotypic ratio: 3 wire-haired : 1 smooth-haired
544
What is the probability of all puppies being smooth-haired (ww) in a Ww × Ww cross?
Statistically possible due to chance; 25% chance per pup
545
How can a dog's genotype be determined without DNA?
Perform a test cross with a known homozygous recessive (ww)
546
Which allele is likely wild-type in the case of wire-haired dogs?
w (smooth hair) is likely wild-type
## Footnote
Typically recessive and associated with the non-mutant/ancestral form.
547
Why did Mendel use homozygous lines in his experiments?
He used true-breeding lines for consistent, predictable results in crosses.
548
Does equal segregation of alleles into daughter cells occur in mitosis, meiosis, or both?
Meiosis only
549
What are the possible genotypes for blood type B?
IBIB or IBi
550
What are the parental genotypes that could result in a child with blood type B?
* IBIB × ii
* IBi × IBi
* IBIB × IBi
551
What is haploinsufficiency in mice coat color genetics?
A^Y A^Y leads to lethal phenotype (mice die)
552
What is codominance in mice coat color genetics?
A^Y A results in all hairs black or white, mixed
553
What is haplosufficiency in mice coat color genetics?
A A results in all hairs black
554
What is the phenotype and genotype for entirely black cats?
Entirely black: Oᵇ/Oᵇ ; S/S or S/s
555
What is the probability that a daughter of a father with a dominant late-onset neurological disease will inherit it?
50%
556
What are the results of the cross between an orange male (ZᴼZᴼ) and a black female (ZᴮW)?
Sons: ZᴼZᴮ
Daughters: ZᴼW
557
Does Mendel’s First Law apply to sex chromosomes?
Partially
558
What is the relationship between the Oᵇ and O⁺ alleles in cats?
Codominance
559
Show the genotype-to-phenotype for F8 gene (X-linked recessive, hemophilia A) for females.
* FB/FB: Female, normal
* FB/F8: Female, carrier
* F8/F8: Female, affected
560
Show the genotype-to-phenotype for F8 gene (X-linked recessive, hemophilia A) for males.
* FB/Y: Male, normal
* F8/Y: Male, affected
