Modes of Inheritance/Genes Revision U1 AOS 1 Flashcards
1
Q
Pedigree chart
A
shows the inheritance of a particular trait over many generations and can be used to determine modes of inheritance
2
Q
main pedigree conventions
A
squares = males
circles = females
diagonal line in the circle or square means = deceased
horizontal line = married
vertical line = offspring
roman numerals = represent gens
numbers = birth order of offspring
3
Q
fast + slow method to pedigrees
A
- are all generations affected
y = recessive - for every female affected are the fathers affected?
are all the sons affected?
y = x linked recessive
n = autosomal recessive
n = dominant
when an affected male is mated with an unaffected female do all the daughters show the trait?
y = x linked dominant
n = autosomal dominant
4
Q
Genotypes
A
the complete set of an organisms genetic material
5
Q
DNA
A
Deoxyribonucleic acid ( DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development of an organism
6
Q
Trait
A
specific characteristic of an organism
7
Q
Affected individual
A
has the trait
8
Q
Unaffected individual
A
does not have the trait, buy they may be heterozygous for the trait making them a carrier which allows them to pass it on to future offspring.
9
Q
Generation
A
10
Q
Autosomal dominant inheritance
A
Both sexes are affected equally (approximately)
Two unaffected parents CANNOT have an affected offspring
TWO affected parents CAN have an unaffected child
The trait tends to appear in most, if not all, generations
11
Q
Autosomal recessive inheritance
A
Both sexes are affected equally (approximately)
If both parents are affected, all offspring will be affected
Two unaffected parents CAN have an affected child
May skip some generations
12
Q
X-linked dominant
A
Over many generations, more females than males will be affected
DOES NOT skip generations
Two unaffected parents CANNOT have an affected child
Affected sons must have an affected mother
Affected daughters must have an affected mother or an affected father
13
Q
X-linked recessive
A
Over many generations, more males than females will be affected
Affected sons can be born to unaffected (carrier) mothers, thus the trait can skip generations
The allele for the trait is never passed from father to son because the father passes on the Y chromosome only
All daughters of affected fathers are carriers (unless they also inherited the recessive allele from their mother, in which case they are affected)
14
Q
Y - linked
A
Only males are affected
It is passed from father to all sons
DOES NOT skip generations
15
Q
-biomacromolecules ( lipids, carbohydrates,
A
16
Q
proteins, including disaccharides)
A
17
Q
-enzymes ( lactase)
A
18
Q
-fermentation ( bacteria)
A
19
Q
-gene regulation
A
20
Q
- evidence for evolution and coevolution
A
21
Q
gene
A
genes are made up of DNA and are passed on from parents to their offspring, some genes may code for proteins while others don’t
22
Q
chromosome
A
23
Q
genome
A
24
Q
karyotype
A
25
Phenotypes
26
Dihybrid cross
27
True breeding
28
Heterozygous
29
F1 generation + F2 generation
30
Incomplete dominance
31
Co dominance
32
Eye colour
Skin colour
Height
are examples of polygenic traits that are controlled by multiple genes not just one
33
○ Interphase
○ Prophase
○ Metaphase
○ Anaphase
○ Telophase
Interphase: The cell is undertaking metabolic activity and preparing for the asexual reproduction (mitosis).
Prophase: Chromatin in the nucleus starts to condense, resulting in the nucleolus disappearing. Centrioles move to opposite ends of the cell.
Metaphase: Chromosomes are aligned by spindle fibers along the center of the cell nucleus. This ensures the proper chromosome separation for each new nucleus.
Anaphase: The paired chromosomes separate
and move to opposite sides of the cell.
Telophase: Chromatids arrive at opposite poles of the cell, new membranes form around the nuclei.
Telophase: Chromatids arrive at opposite poles
of the cell, new membranes form around the nuclei.
34
How is meiosis DIFFERENT to mitosis?
How is meiosis SIMILAR to mitosis?
35
Genetic diversity created during meiosis due to:
* Independent assortment of homologous chromosomes
* Crossing over (recombination)
36
Interphase
Interphase: The cell is undertaking metabolic activity and preparing for the asexual reproduction (mitosis).
37
define the following
1. spindle Fibre
2. PMAT
3. Nucleus Membrane
4. Chromosome
5. Centriole
6. Cell membrane
1. Spindle Fibre
2. PMAT
3. Nucleus Membrane
4. Chromosome
5. Centriole
6. Cell membrane
38
Cytokinesis
The process of separating the two new cells from each other
In animals uses a contractile ring to pinch the two cells apart from each other
39
DISTINGUISH between cytokinesis in animal and plant cells.
cytokinesis in animal cells
microfilaments form and create cleavage furrow which pinches in to create separate cells
cytokinesis in plant cells
the cell plate forms which creates separate cells
40
Prior to meiosis 1, non-sister chromatids swap sections of their DNA. Can you explain the difference between sister and non-sister chromatids?
sister chromatids are identical whereas non sister chromatids are have the same genes but not the same alleles.
41
How is meiosis (here) different to mitosis?
Unlike in mitosis, meiosis is a process of 2 cell divisions, ultimately creating 4 daughter cells that are haploid rather than the usual diploid.
42
chiasma
A chiasma can occur anywhere along the length of a chromosome. Multiple chiasmata may form between non-sister chromatids for any given pair of homologous chromosomes.
43
what could happen if one goes through meiosis normally vs chromosome non disjunction
this means the chromosomes have failed to separate into 4 cells this results in non disjunction where cells are produced lacking a chromsome or having an additional copy.
44
Karyotypes
Karyotypes as a visual representation that can be used to identify chromosome abnormalities
45
Prophase
Prophase: Chromatin in the nucleus starts to condense, resulting in the nucleolus disappearing. Centrioles move to opposite ends of the cell.
46
Metaphase
Metaphase: Chromosomes are aligned by spindle fibers along the center of the cell nucleus. This ensures the proper chromosome separation for each new nucleus.
47
Anaphase
Anaphase: The paired chromosomes separate
and move to opposite sides of the cell.
48
Telophase
Telophase: Chromatids arrive at opposite poles of the cell, new membranes form around the nuclei.
49
homologous chromosomes
Chromosome come in pairs that are described as homologous because they have same
size
banding pattern (indicating the location of their genes or gene loci)
centromere position
50
karyotypes
In a karyotype, the images of a cell’s chromosomes are arranged according to these features into matching or homologous pairs. This can allow you to see all of the chromosomes in a diploid somatic cell, e.g. for humans:
23 pairs of homologous chromosomes
one set of 23 maternal chromosomes (from mother)
one set of 23 paternal chromosomes (from father)
92 sister chromatids
51
what can karyotypes be used to determine
Karyotypes can be used to determine sex e.g. in humans
one pair determines sex (males are XY and females are XX) i.e. sex chromosomes
remaining chromosomes are autosomes
52
why does sex determination differ in species
Sex determination differs in species. It can also be influenced by environmental factors as well as the chromosomes
e.g. green turtle eggs incubated at 31OC or higher are all females and at 27OC or below are all males. This is called temperature-dependent sex determination.
53
Various changes can occur involving chromosomes, including:
Various changes can occur involving chromosomes, including:
Changes in the total number of chromosomes
Changes involving part of one chromosome
Changed arrangements of chromosomes
54
what is aneuploidy and how do we identify it?
Karyotypes can be used to identify aneuploidy
abnormal (±) chromosome number
due to nondisjunction of homologous chromosomes during anaphase I/II of meiosis (or translocation of whole chromosome)
e.g. trisomy - Down’s Syndrome (21), Edward Syndrome (18), Patau Syndrome (13)
55
is the diploid chromosome number unique to each species?
The diploid chromosome number is unique to each species.
The species have two of each chromosome (diploid)
human diploid number is 46
cat diploid number is 38
Drosophila (fruit fly) diploid number is 8
sheep diploid number is 54
cabbage diploid number is 18
56
what is polyploidy?
Karyotypes can show polyploidy
whole complements or sets of chromosomes lost or gained e.g. 3n, 4n etc.
due to total non-disjunction during mitosis or meiosis
common in plants
57
using definitions connect genes, genomes, alleles
genomes are a complete set of an organism's replicated DNA. Genes are made up of DNA and code for molecules to create proteins. Alleles are variations of the same gene.
58
what are an organisms traits linked to?
An organism’s traits or characteristics are either directly or indirectly due to the proteins produced by their cells. Examples:
59
what are the types of proteins
Structural proteins
hair keratin
Enzymatic proteins
lactase which digests lactose in milk and dairy products
Hormonal proteins
oestrogen and testosterone which determine your sexual characteristics
60
why do we have 2 copies of almost every gene
do the X and Y chromsomes have the same genes
how is the specific information coded
Diploid (2n) cells have 2 copies of (almost) every gene as we inherited one copy from each parent. The X and Y chromosomes, however, have different genes
The specific information are coded by the gene variants (alleles).
61
Different alleles may code for a different proteins depending on:
Whether it occurs in a coding region
Whether the resultant codon adds a different amino acid
62
difference between genes, chromosomes and DNA
63
what are chromosomes?
why and how is the DNA tightly packaged?
when do chromosomes become visible and what do they look like?
Chromosomes are the structures formed when very long double stranded DNA molecules are tightly coiled around proteins called histones to form nucleosomes. This allows the DNA to be supercoiled and packaged such that
it can fit inside the nucleus of cells
a reproducing cell can pass on its genetic material
Chromosomes are visible as thread-like structures during cell division.
64
what does it mean when genes are linked
Genes that are located close together on the same chromosome are said to be linked. This means that they are inherited together.
Chromosomes carrying the same gene loci
65
eukaryotic
the eukaryotic cell cycle refers to the
66
Think about what happens during prophase, and why?
67
condense
68
centrioles and centromeres
69
CENTROMERE, KINETOCHORE
70
Complete Dominance
An allele or phenotype is either expressed or not.
In a heterozygous individual…
dominant trait is expressed when at least one allele for the trait is present
→ trait expressed by heterozygous individual
recessive trait is expressed only when there are two alleles for the trait present
→ trait can be masked in a heterozygous individual
→ trait is expressed only by a homozygous individual
71
recessive trait is expressed only when there are two alleles for the trait present
72
dominant trait is expressed when at least one allele for the trait is present
73
The dominant phenotype is expressed as long as ONE copy of the allele is present
74
Albinism is controlled by the TYR gene, which controls the enzyme involved in pigment production.
75
‘normal’ phenotype is expressed in homozygote AND heterozygote
⇩
‘normal’ phenotype is dominant
⇩
allele for ‘normal’ is represented by UPPERCASE A
76
albino phenotype is expressed ONLY in homozygote
⇩
albino phenotype is recessive
represented by lowercase allele
⇩
allele for albino is represented by lowercase a.
77
Co-Dominance
Both alleles or phenotypes are equally expressed (i.e. neither of the traits is recessive to another).
In a heterozygous individual both alleles/phenotypes are fully expressed.
78
Allele symbols:
R1 = Red
R2 = White
Both UPPERCASE because both are Dominant.
79
ABO Blood type is under both complete AND co-dominant control of multiple alleles for the same gene locus. The ABO gene codes for antigen molecules on the surface of red blood cells.
IA - A antigen
IB - B antigen
i - no antigen produced
80
genotype and phenotype of ABO blood types
81
IA and IB are co-dominant to each other
IA and IB are both dominant to i
82
incomplete dominance
Neither allele nor phenotype is completely dominant.
In a heterozygous individual the phenotype is blended or intermediate.
83
Complete Dominance Involving Multiple Genes
The traits we have been studying so far are controlled by a single gene at a single gene locus. Monogenic traits produce discontinuous variation where there are discrete phenotypic phenotypes.
84
In some cases, a visible phenotype may be the result of an interaction between multiple genes at different gene loci. Polygenic traits produce continuous variation because each gene has a small, but cumulative effect on the phenotype. This continuous variation produces a normal distribution curve (bell shaped).
85
Also keep in mind that variation can be due to environmental and genetic factors:
Phenotype = Genotype + Environment
86
polygenic inheritance
Trait is controlled by more than one pair of genes
More gradations in phenotype
Larger number of genes involved makes phenotype appear continuous
Environment assists in the smoothing out the curve
Often seen as a bell curve
e.g. height of person
87
examples of polygenic inheritance
Skin or eye colour are examples polygenic traits controlled by multiple genes that can be located on different chromosomes. In polygenic inheritance there is no dominant phenotype like we have been studying (Mendelian inheritance). Each allele gives a cumulative effect on the phenotype rather than masking the other phenotype.
88
The pigment melanin is responsible for dark skin is under the control of at least three genes. Let’s represent the the hypothetical alleles for these 3 gene loci:
89
Three loci, each with two alleles
(P, p, Q, q, R, r)
Height of the plant is determined by the number of uppercase alleles
e.g. Tallest is PPQQRR and shortest is ppqqrr
This also means that plants with the same number of uppercase alleles are the same height
e.g. PPQqrr, ppQQRr, PpQqRr
90
The graph shows frequency of each height (number of uppercase alleles) showing ‘normal distribution’
91
How can epigenetics explain current and future differences between the Losordo twins?
92
epigenetics
Epigenetics is the study of how cells with identical genotypes can show different phenotypes, i.e. differences NOT due to genes. Individuals displaying epigenetic inheritance can sometimes even pass on these differences to future generations.
93
Epigenetic factors
Change how DNA in cells is packaged e.g. winding around histone proteins
Change how histones are labelled e.g. methyl groups act as ‘tags’ which affect the ability of RNA polymerase enzyme to bind to the DNA and carry out transcription.
94
Epigenetic factors are factors that can change how genes are ‘switched on or off’ by affecting transcription. They can be turned on and off, and are usually not passed on to gametes.
95
Since epigenetic factors can alter which genes are expressed, they can be linked to the expression of some diseases e.g. fewer methyl tags on tumour-suppressor genes can provide protection against cancer.
96
Embryonic Development
The stem cells in the developing embryo differentiate into hundreds of different cell types e.g. neurons, muscle cells, epidermal cells.
Since all of the cells in the embryo have come from the mitotic division of a single zygotic cell they all have the same genotype.
Epigenetic factors switch on and off certain genes in certain cells causing them to develop into different cell and tissue types.
97
X-Inactivation
Early in embryonic development of females, one of the two sex chromosomes (X) is switched off in all somatic cells.
This means that genes from only one X-chromosome are active since extra copies of genes or chromosomes can affect normal development.
The epigenetic tags responsible for X-inactivation are passed on to all cells created by mitosis so that all daughter cells have the same inactivated X chromosome.
98
list examples of epigentic inheritance
Embryonic Development
X-Inactivation
99
Q1. Explain how epigenetic ‘tags’ on histone proteins can cause genes to be ‘silenced’.
Q2. Explain whether or not epigenetics is similar to genetic mutations.
100
Mendelian Genetics
Dominant allele written with capital letter e.g. R
Recessive allele written with lower case of same letter e.g. r
Genotype:
Homozygous RR or rr
Heterozygous Rr
Phenotype:
round (RR or Rr), wrinkled (rr)
101
Why do we use Pedigree Analysis?
Since crosses between humans cannot be set up and produce only a limited number of offspring, studying human genetics is difficult.
When more than one individual in a family is afflicted with a disease, it suggests that the disease might be inherited.
It is therefore useful to study their family trees using pedigree analysis, where the presence of a given characteristic is examined over a number of generations.
A pedigree is simply a family tree that uses a particular set of standardized symbols.
102
Some traits are sex-linked.
This means that the genes for the traits are located on a sex chromosome - usually X rather than Y chromosome (because the X chromosome is bigger and contains more genes)
103
Sex-linked recessive conditions incl. haemophilia, baldness and colour-blindness are more common in males. Since males are hemizygous (i.e. XY). So whichever allele is found on a male’s sex chromosome is expressed.
104
Autosomal dominant + Autosomal recessive
if a trait is autosomal dominant or recessive it means it is not linked to the sex chromsomes - if it is dominant it means the trait is more likely to be expressed, if it is recessive then it is less likely to be expressed
105
Compare the similarities and differences between genetic testing and genetic screening
genetic screening refers to the testing of a population as part of an organisation in order to detect inherited disorders
genetic testing refers to the testing of specific of an individual for various reasons eg
106
Hybridisation
Hybridisation: breeding two individuals from distinct populations to produce hybrid offspring
107
Independent Assortment
We now know that the factors that lie on different chromosomes assort independently because the chromosomes segregate randomly during meiosis
When gametes are formed the factors for each characteristic are sorted independently
108
linked vs independent assortment
Linked
Need to be on the same chromosome
More likely if closer together on the same chromosome
Unlinked
Always if genes are on different chromosomes
More likely the further apart the genes are if on the same chromosome.
109
What must be the same for two genes to be linked?
Chromosome number
Allele color
Parent that they came from
Size of the gene
110
2. How does meiosis cause Mendel’s law of independent assortment?
A. Linked genes are randomly separated.
B. The chromosome number is divided twice.
C. Crossing-over occurs in Anaphase I.
D. Alleles that are not in the same linkage group are segregated.
111
3. Are genes on the same chromosome always linked? Justify your answer.
112
what causes genetic diversity and why is this important?
Crossing over results in the formation of new recombinant chromatids each with its own unique combination of alleles.
This adds to the genetic diversity of the resulting haploid daughter cell as the sister chromatids that they will inherit
Pairs of homologous chromosomes line up on opposite sides
of the metaphase plate. The resulting combination of alleles in
each daughter cell is randomised since what is inherited depends on
which side of the metaphase plate each chromosome is positioned.
The number of di*erent combinations in humans is around 8 million it
are no longer identical.
