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Principles of Inheritance and Variation Flashcards

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1
Q

What is the process by which characters are passed on from parent to progeny?

A

Inheritance

Inheritance is the basis of heredity.

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2
Q

What is the degree by which progeny differ from their parents called?

A

Variation

Variation can be due to genetic differences or environmental factors.

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3
Q

Who conducted hybridization experiments on garden peas to propose the laws of inheritance?

A

Gregor Mendel

Mendel’s work laid the foundation for modern genetics.

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4
Q

What did Mendel call the units of inheritance that are now known as genes?

A

Factors

Mendel proposed that these ‘factors’ are stably passed down from parent to offspring.

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5
Q

What are alleles?

A

Slightly different forms of the same gene

Alleles code for contrasting traits.

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6
Q

In Mendel’s experiments, what trait was dominant in the F1 generation when crossing tall and dwarf pea plants?

A

Tall

The dominant trait is expressed in the phenotype of the F1 generation.

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7
Q

What was the phenotypic ratio observed in the F2 generation of Mendel’s monohybrid cross?

A

3:1

This ratio reflects the dominant and recessive traits in the offspring.

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8
Q

What is the purpose of a Punnett Square?

A

To calculate the probability of all possible genotypes of offspring in a genetic cross

It visually represents the combination of alleles from the parents.

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9
Q

Fill in the blank: Genes that code for a pair of contrasting traits are known as _______.

A

Alleles

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10
Q

What do we call the offspring of the F1 generation?

A

Filial 2 (F2)

The F2 generation results from the self-pollination of F1 plants.

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11
Q

True or False: In a monohybrid cross, the recessive trait is expressed in the F1 generation.

A

False

The recessive trait is only expressed in the F2 generation.

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12
Q

What is the genotype of a true-breeding dwarf pea plant?

A

tt

True-breeding plants have identical alleles for a trait.

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13
Q

What does it mean for an organism to be heterozygous?

A

It has two different alleles for a gene

For example, Tt is heterozygous for the height gene.

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14
Q

What is the significance of Mendel’s large sampling size in his experiments?

A

It gave greater credibility to the data collected

Larger samples help ensure that results are statistically significant.

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15
Q

What is the genotypic ratio of the F2 generation in Mendel’s monohybrid cross?

A

1:2:1

This ratio represents the genotypes TT, Tt, and tt.

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16
Q

What trait does the capital letter represent in Mendel’s notation?

A

The dominant trait

For example, T represents the tall trait.

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17
Q

What trait does the lowercase letter represent in Mendel’s notation?

A

The recessive trait

For example, t represents the dwarf trait.

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18
Q

What binomial expression represents the genotypes of gametes bearing genes T or t?

A

(1/2T + 1/2t)²

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19
Q

What were the genotypic ratios obtained from the expansion of the expression (1/2T + 1/2t)²?

A
  • 1/4 TT
  • 1/2 Tt
  • 1/4 tt
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20
Q

What conclusion did Mendel reach regarding the genotype of dwarf F2 plants?

A

The genotype of the dwarfs was homozygous – tt.

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21
Q

What is a test cross?

A

A cross between an organism showing a dominant phenotype and a recessive parent to determine the genotype.

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22
Q

What is the purpose of a test cross?

A

To determine the genotype of a dominant phenotype organism.

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23
Q

What are the two general rules proposed by Mendel for inheritance in monohybrid crosses?

A
  • Law of Dominance
  • Law of Segregation
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24
Q

What does the Law of Dominance state?

A
  • Characters are controlled by discrete units called factors
  • Factors occur in pairs
  • In a dissimilar pair of factors, one member dominates the other
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25
What does the Law of Segregation explain?
Alleles segregate during gamete formation so that each gamete receives only one of the two factors.
26
What is incomplete dominance?
A genetic scenario where the F1 phenotype is intermediate between the two parental phenotypes.
27
Provide an example of incomplete dominance.
Flower color in snapdragons (Antirrhinum sp.) where red (RR) and white (rr) produce pink (Rr) offspring.
28
What is co-dominance?
A genetic scenario where both parental phenotypes are expressed in the offspring.
29
How is ABO blood grouping an example of co-dominance?
Both IA and IB alleles express their sugars in the red blood cells when present together.
30
What is meant by multiple alleles?
More than two alleles govern the same character.
31
What is the expected phenotypic ratio from a dihybrid cross?
9:3:3:1
32
What does Mendel’s Law of Independent Assortment state?
Segregation of one pair of traits is independent of the other pair during hybrid formation.
33
What is the significance of the Punnett square in genetics?
It helps visualize the segregation of alleles and predict genotype and phenotype ratios.
34
What did Mendel conclude about the dominant and recessive traits in his dihybrid cross?
Yellow color was dominant over green and round shape was dominant over wrinkled.
35
What are the expected genotypes in the F2 generation of a dihybrid cross?
RrYy, RRYy, Rryy, rrYY, rrYy, rryy
36
What advancement in microscopy contributed to the rediscovery of Mendel's work?
Discovery of chromosomes and observation of their behavior during cell division.
37
What are chromosomes?
Structures in the nucleus that double and divide during cell division.
38
When was Mendel's work on inheritance rediscovered?
In 1900 by de Vries, Correns, and von Tschermak.
39
What structures in the nucleus were discovered that double and divide before cell division?
Chromosomes ## Footnote Chromosomes are visualized by staining and are essential for understanding cell division.
40
Who noted the parallel behavior of chromosomes and genes?
Walter Sutton and Theodore Boveri ## Footnote They used chromosome movement to explain Mendel’s laws.
41
What is the chromosomal theory of inheritance?
The idea that chromosomal segregation leads to the segregation of gene pairs ## Footnote This theory was developed by Sutton and Boveri.
42
What organism did Thomas Hunt Morgan use for his genetic studies?
Drosophila melanogaster ## Footnote This fruit fly is ideal for genetic studies due to its rapid life cycle and clear sex differentiation.
43
What is linkage in genetics?
The physical association of genes on a chromosome ## Footnote Morgan coined this term after observing that certain genes do not assort independently.
44
What does recombination refer to in genetics?
The generation of non-parental gene combinations ## Footnote This occurs during the process of crossing over in meiosis.
45
What is polygenic inheritance?
Inheritance controlled by three or more genes ## Footnote Traits such as human height and skin color are examples of polygenic traits.
46
Define pleiotropy.
A single gene exhibiting multiple phenotypic expressions ## Footnote An example is phenylketonuria, which affects multiple traits.
47
What is the XO type of sex determination?
A mechanism where all eggs have an additional X-chromosome, while sperm may or may not have it ## Footnote Seen in certain insects like grasshoppers.
48
What is the XY type of sex determination?
A mechanism where females have XX chromosomes and males have XY chromosomes ## Footnote Found in humans and Drosophila.
49
How does sex determination in honey bees differ from that in humans?
Honey bees exhibit haplodiploidy, where fertilized eggs develop into females and unfertilized eggs develop into males ## Footnote Males are haploid with half the chromosomes of females.
50
What is mutation in genetics?
An alteration of DNA sequences that leads to changes in genotype and phenotype ## Footnote Mutations can be point mutations or chromosomal aberrations.
51
What is pedigree analysis?
The study of inheritance patterns in families to understand genetic disorders ## Footnote This method helps to trace traits through generations.
52
Fill in the blank: The presence of an X and Y chromosome determines the ______ characteristic.
male ## Footnote In humans, the presence of XX results in female characteristics.
53
True or False: Chromosomes segregate independently during gamete formation.
True ## Footnote This principle is part of Mendel's laws of inheritance.
54
What genetic mapping technique was developed by Alfred Sturtevant?
Mapping the position of genes based on recombination frequency ## Footnote This technique is foundational for modern genetics.
55
What is the concept of pedigree analysis?
Pedigree analysis is the study of inheritance patterns of traits in several generations of a family, represented in a family tree.
56
What role does DNA play in inheritance?
DNA is the carrier of genetic information transmitted from one generation to the next without change.
57
Define mutation in genetics.
A mutation is an alteration or change in the genetic material.
58
What are the two broad categories of genetic disorders?
Mendelian disorders and Chromosomal disorders.
59
What are Mendelian disorders primarily determined by?
Alteration or mutation in a single gene.
60
List some common Mendelian disorders.
* Haemophilia * Cystic fibrosis * Sickle-cell anaemia * Colour blindness * Phenylketonuria * Thalassemia
61
What is the inheritance pattern of haemophilia?
Haemophilia is a sex-linked recessive trait transmitted from carrier females to male progeny.
62
Fill in the blank: Colour blindness is a _______ disorder.
sex-linked recessive
63
How does sickle-cell anaemia occur?
Sickle-cell anaemia results from a mutation that substitutes Glutamic acid with Valine in the beta globin chain of hemoglobin.
64
What characterizes thalassemia?
Thalassemia is an autosome-linked recessive blood disease affecting the synthesis of globin chains in hemoglobin.
65
What causes Down’s syndrome?
Down's syndrome is caused by trisomy of chromosome 21, resulting in an extra copy of this chromosome.
66
What is Klinefelter’s syndrome?
Klinefelter's syndrome is caused by an additional X chromosome, resulting in a karyotype of 47, XXY.
67
What is Turner’s syndrome?
Turner's syndrome is caused by the absence of one X chromosome, resulting in a karyotype of 45, X0.
68
What is the total number of chromosomes in a normal human cell?
46 chromosomes (23 pairs).
69
Define the Law of Dominance.
The Law of Dominance states that dominant characters are expressed when factors are in heterozygous condition.
70
What does the Law of Segregation state?
The Law of Segregation states that characters segregate during the formation of gametes.
71
What is the difference between homozygous and heterozygous?
Homozygous has identical alleles for a trait, while heterozygous has different alleles for a trait.
72
What does the term co-dominance mean?
Co-dominance occurs when both alleles in a heterozygote are fully expressed.
73
What is the significance of the Punnett Square?
The Punnett Square is used to represent different combinations of gametes and predict offspring phenotypes.
74
True or False: All characters show true dominance.
False.
75
What is a point mutation?
A point mutation is a change of a single base pair in DNA.
76
Who first described the principles of inheritance?
Mendel.
77
What is the chromosomal theory of inheritance?
The chromosomal theory of inheritance links Mendel's laws of segregation and independent assortment to chromosome behavior during meiosis.
78
What is aneuploidy?
Aneuploidy is the gain or loss of one or more chromosomes due to failure of segregation during cell division.
79
What is polyploidy?
Polyploidy is the condition where there is an increase in a whole set of chromosomes.
80
List two examples of autosomal genetic disorders.
* Sickle-cell anaemia * Phenylketonuria
81
What is the expected phenotype distribution when crossing TtYy with Ttyy?
* Tall and green * Dwarf and green

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