Genes Flashcards
(124 cards)
1
Q
What is heredity?
A
The study of inheritance.
2
Q
What is population genetics?
A
the study of the gene pool organism over time.
3
Q
What are molecular genetics?
A
The study of the molecular structure and function of genes.
4
Q
What is a gene and how is it defined?
What about to a molecular geneticist?
A
A gene is an inherited factor that affects the characteristics of an individual.
It is defined by the affect on the phenotype of the organism.
It is also part of a chromosome involved in the transcription of DNA into RNA.
5
Q
What is a wild type?
A
Functional
6
Q
What is a loss of function?
A
non functional. usually recessive.
7
Q
What is a gain of function?
A
A new or enhanced function. Usually dominant.
8
Q
What is the difference between a wild type and a mutant?
A
wild type & loss of function = wild type.
wild type and gain of function = mutant.
9
Q
What is an exon?
A
Code for proteins, they express sequences.
Part of DNA that is converted into mRNA.
10
Q
What is an intron?
A
Do not code for proteins. They intervene sequences.
Present in the inital RNA transcript, and must be removed for the mRNA to do its job.
11
Q
What happens if a LOF allele is dominant?
A
Haploinsufficiency.
12
Q
Describe mitosis.
A
Somatic cells, producing two genetically identical daughter cells.
2 x 2n
13
Q
Describe meiosis.
A
produces 4 haploid daughter cells.
4 x n
14
Q
Describe interphase.
A
All the cells DNA is replicated, each chromosome consists of two identical sister chromatids joined at the centromere.
Cell now has four copies of each chromosome as opposed to two.
15
Q
Describe the stages of meiosis.
A
PMAT I & II
16
Q
What is a bivalent?
A
A homologous pair of chromosomes, each consisting of two sister chromatids, paired for meiosis.
17
Q
Compare meiosis and mitosis. No of divisions Products Chromosome no Bivalents formed Crossing over occurring
A
Mitosis. Meiosis
No of divisions:
One. Two
Products:
Two identical Four different
daughter cells
Chromosome no:
Maintained. Halved
Bivalents:
No. Yes
Crossing over:
No. Yes
18
Q
What is the locus?
A
The position of a gene on a chromosome.
19
Q
What is crossing over?
A
When lengths of DNA are swapped from one chromatid to another.
20
Q
What are the consequences of meiosis?
A
Gametes are haploid (somatic cells are diploid).
Genetically
different from each other because …
•chromosome orientation at Metaphase I is random
•crossing-over shuffles segments of homologous
chromosomes
21
Q
How does meiosis lead to genetic variation?
A
Crossing over shuffles alleles.
Genetic reassignment due to the random distribution of maternal and paternal chromosomes during meiosis I.
Genetic reassortment due to the random distribution and segregation of the sister chromatids at meiosis II.
Random mutation.
22
Q
Describe how crossing over occurs.
A
Prophase I.
The homologous chromosomes pair and come together to form Bivalents.
Non sister chromatids wrap around each other very tightly and attach at the chiasmata.
The chromosomes may break at these points, which then rejoin to ends of the chromatids in the same bivalent.
The sections that swap contain the same genes but different alleles.
Produces new combinations of alleles on the chromatids.
23
Q
Where do chromatids join during crossing over?
A
At the chiasmata.
24
Q
Describe how the reassortment of chromosomes occurs.
A
In metaphase I there is a random distribution of chromosomes on the spindle equator.
Each gamete acquires a different mixture of maternal and paternal chromosomes.
25
Describe how the reassortment of chromatids occurs.
Happens in metaphase II.
The chromatids are randomly distributed on the spindle equator.
Because of crossing over the sister chromatids are not identical.
26
Learn mitosis cycle.
notes.
27
How are sister chromatids joined?
By sister chromatic cohesion.
28
When are homologous chromsomes seperated?
anaphase I
29
How many bivalents can be seen at prophase I of meiosis in humans?
3 bivalents each with 4 chromatids. In P1 2n=6.
30
What is Mendels first law?
Principle
of Segregation: Alleles of a single gene segregate randomly
and equally into gametes
31
What is the freq of the dominant B allele in a population of 100 with the genotypes: 30 BB, 60 Bb, 10 bb,
0.6 since (30 x 2) + 60 = 120
| 120=200
32
What is the ratio for a monohybrid cross?
| RR x rr
3:1 in the F2 generation.
| All dominant in F1.
33
What is the ratio for a dihybrid cross?
| RR yy x rr YY
9:3:3:1 in F2.
34
What is Mendel's second law?
Principle of independent assortment. Alleles from different genes segregate randomly into gametes.
35
Why are the four offspring of meisis different?
Independent assortment of maternal/paternal chromosomes.
| Crossing over.
36
What is Mendel's theory of inheritence?
•Characters are distinct, and hereditary
determinants (genes) are particulate in nature
•Each adult has two genes for each character-different forms of the genes are called alleles
•Members of the gene pair segregate equally into
gametes, so that each gamete has only one of the
two genes (Mendel’s first law)
•Fusion of the gametes at fertilisation restores the
pair of genes and is random
•Different genes assort independently in gametes
(Mendel’s second law)
37
What is incomplete dominance?
Heterozygotes show an intermediate phenotype.
| Ratio 1:2:1
38
What is co dominance?
Heterozygotes show phenotype of both alleles.
| Blood cells.
39
Describe multiple alleles.
There may be more than two alleles for a gene.
40
What is Pleiotropy?
When a gene may influence more than one trait.
ie. Sickle cell haem give resistance to malaria.
Heterozygote HbA Hbs have highest fitness.
41
Describe lethal alleles.
Can cause skewed phenotypic ratios.
42
Describe Achondroplasia.
homozygous for it causes death. heterozygote results in a dwarf. neither parent affected, arises from a new mutation.
43
What does a 9:3:3:1 ratio indicate?
2 genes involved - 4 phenotypes.
44
What is epistasis?
The interaction between two or more genes that control a single phenotype.
Usually one gene masks the phenotypic effect of another.
45
What is the recessive epistatic ratio?
9:4:3
46
Why is the albino c allele epistatic to all other coat colour genes?
the albino allele is a recessive loss of function mutation in the enzyme Tyrosinase which is required for the synthesis of melanin pigments in melanocytes.
47
What is the dominant epistatic ratio?
12:3:1
48
What is proliferation?
Division.
49
Why is the dominant white W allele epistatic to other coat colour genes?
dominant white is a dominant loss-of-function mutation in a transmembrane growth factor receptor required for proliferation (division) and migration of melanocytes
50
What is does penetrance measure?
The % of individuals with a given genotype who exhibit the expected phenotype.
51
What does expressivity measure?
The extent to which a given genotype is expressed at the phenotypic level.
52
Describe allelic variation.
Alleles may vary in the severity of the phenotypes they cause.
53
Give an example of allelic variation.
Cystic fibrosis - over 1800 mutations found.
54
How can individuals with the same mutation have varying phenotypes?
Due to modifier genes.
55
What is phenylketonuria? (PKU)
Caused by deficiency in converting phenylalanine to tyrosine.
Leads to brain damage, seizures and mental retardation.
Treated with low phenylalanine diet.
56
What are epigenetics?
phenotype that can be inherited but not due to a change in the base sequence in DNA.
57
What are autosomes?
Non sex chromosomes.
58
What does hetermorphic mean?
Different, ie in size, shape.
59
Compare the X and Y chromsomes.
X is much larger than Y, the differential region of the X contains most sex linked genes, the Y contains many fewer genes.
60
What is the pseudoautosomal region?
A region shared by both X and Y chromsomes. About 30 genes. Required for X-Y pairing in male meiosis.
61
What does homogametic and heterogametic mean?
Homogametic XX - female.
| Heterogametic XY - male.
62
What is aneuploidy?
| How has it given evidence that the Y chromosome confers maleness.
Wrong number of chromsomes.
XO are female.
XXY are male.
63
What is the SRY gene.
The Sex determining Region on the Y.
The only gene needed for maleness.
Mutation of this gene can give XY females.
64
How does the SRY gene work?
It is a DNA binding protein/transcription factor that regulates the expression of genes necessary for testis formation.
65
How is sex determined in Drosophila?
```
the ratio of X chromosomes to autosome sets.
Cell autonomous?, Y has no influence.
If X:A > 1 female
X:A < 0.5 male.
0.5 > X:A > 1 Intersex.
```
66
Who studied sex linked genes in Drosophila?
Thomas Hunt Morgan.
67
How can mutant Dosophila be identified?
normal eye colour is red, mutant has white.
| mutant w-, wild type w+
68
Describe Drosophila's chromosomes.
3 homomorphic pairs , 1 heteromorphic pair.
| All egs have one X chromosome, sperm are 50/50 X/Y.
69
Where do most sex linked inheritances occur?
on the X chromosome.
70
What is the ZW system and where does it occur?
Chickens & moths.
Males are homogametic ZZ.
Females are heterogametic ZW.
71
What is cell autonomy?
Each cell makes the decision to be male or female, not goverend by hormones.
72
What is a gynandromorph?
Both male and female characteristics.
| Chickens.
73
What is a barr body?
Females have 2 X chromosomes and thus twice the amount of X linked genes. One of the X chromosomes becomes inactiviated, and is visible in interphase as a barr body, highly condensed.
Inactivation is random, it will be either male or female.
An example of epigenetic control of gene expression?
74
What does gene mapping show?
The relative order of genes and the distance between them.
75
What are the types of gene maps and what do they show?
Physical maps:
Shows distance between genes/DNA markers based on measurement of DNA base pairs.
Human genome project using restriction enzymes.
Cytogenetic maps:
Indicates gene positions with respect to cytogenetic markers.
G banding with a number.
Human chromsome 7 - assigned regions and sub bands to give a reference, ie 7q31.2
Linkage maps:
Shows the relative position of genes or markers based on meiotic recombination frequencies (centiMorgan, cM)
The frequency of crossing over in meiosis is proportional to the distance between the genes.
76
What is linkage?
When two genes are found on the same chromosome. Mendel had 2 on 2 different genes. Violates his second law.
77
What are the linkage mapping principles?
The frequency of
crossing-over between two gene loci is proportional to the physical distance
between them on the
chromosome
78
What are the consequences of crossing over?
The frequency of recombinant gametes is
proportional to the frequency of crossing- over.
Independent assortment of genes on different
chromosomes gives 50% recombinant gametes
79
What does a 50% recombinant gamete frequency show us?
Genes are on different chromosomes, or far apart on the same.
80
What does less than a 50% recombinant gamete frequency show us?
Genes are linked on the same chromosome.
81
How do you use a test cross?
Make a double heterozygote.
| Cross the double heterozygote to a tester double homozygous strain.
82
What is genetic distance and how do you calculate it?
Genetic distance = Recombination frequency.
RF= no of recombinant progeny(offspring)/total no of progeny x 100
units are cM. 10% RF = 10 cM.
83
What does recombinant mean?
After crossing over has material from both parents.
84
Why aren't genetic distances exact when using a linkage map?
Numerous cross overs and long distances can underestimate the true distance.
85
```
How can you determine the parental phenotypes from this:
Wild-type 241
Brown 8
Bright red 12
Orange 239
```
Brown and Bright red are recombinant due to low freq.
86
Cystic fibrosis and huntingsons.
notes
87
What is pedigree analysis?
Investigate the occurence of a disease in a family to determine the type of mutation.
88
Learn different pedigree trees,
notes/slides
89
What is genetic heterogeneity?
Mutations in different genes can cause the same disease.
90
What is aneuploidy?
Abnormal number of chromosomes.
91
What is nullisomy?
Loss of a pair of homologous chromosomes.
| 2n -2
92
What is monosomy?
Loss of a single chromosome.
| 2n-1
93
What is trisomy?
one extra chromosome.
2n+1
Down syndrome, often die in utero.
94
What is tetrasomy?
an extra pair of chromosomes.
| 2n + 2
95
What is disjunction?
the normal separation of homologous chromosomes/chromatids to opposite poles at division.
96
What is non disjunction?
The failure of serperation so that 2 chromosomes go to one pole and none to the other.
97
How do aneuploid gametes arise?
By non disjunction during meiosis I or II.
98
What is the normal karyotype for humans?
46.
99
What must a DNA marker be?
Polymorphic - there must be at least 2 alleles present in a significant proportion of the population.
Easy to assay/distinguish accuately.
100
What are commonly used DNA markers?
Short tandem repeats STR's.
| Single nucleotide polymorphisms SNP's.
101
Describe short tandem repeats/microsatellite repeats and minisatellite repeats.
Short sequence of 2-4 nucleotides, usually in non-coding sequences.
mini is >10 nucleotides.
102
Give a use of STR's
Forensic analysis uses PCR which amplifies 12 STRs, which are then seperated by electrophoresis.
103
Describe Single nucleotide polymorphisms.
Most are in non-coding DNA, most common polymorphism in human genome.
In a human 1 in 1000 nucleotides will be different.
104
What is a haplotype?
A particular combination of SNPs in a small region of a chromosome.
Some are unique to particular populations.
105
Describe the DNA found in the mitochondria and chloroplast.
They have prokaryotic features, and circular chromosomes.
106
What is the Endosymbiont theory?
An ancient cell took up prokaryotic organisms, which then became the mitochondria of that cell. Later took up something else which became the chloroplast.
107
What is mtDNA?
| What is in it?
mitochondrial DNA. Closed circle.
Components needed for translation, tRNA and rRNA.
Structural genes for proteins needed for oxidative phosphorylation.
108
What is cpDNA?
| What is in it?
Chloroplast DNA.
Genes encoding tRNA and rRNA for chloroplast translation.
Structural genes for proteins involved in photosynthesis.
109
How are mitochondrial/chloroplast genomes transmitted to the next generation?
uniparentally, usually maternal inheritence.
110
Describe the four o clock inheritence.
Maternally inherits chloroplast, phenotype is that of mother.
111
What is heteroplasmy?
More than one type of mtDNA type, ie normal and mutant. The proportion of mutant mtDNA affects the severity.
112
Describe mendelian traits.
monogenic.
simple relationship between genotype/phenotype.
ie cystic fibrosis.
113
Describe complex traits.
polygenic.
complex relationship between genotype and phenotype.
often strongly influenced by environment - multifactorial.
More complex traits at birth than mendelian.
eg alzheimers, asthma.
Diabetes type II, high BMI or affected parent.
114
What is the polygene hypothesis?
For quantative traits.
Multiple genetic and environmental factors.
ie 1 gene/2alleles = 3 genotypes
3^n genotypes.
115
What is the total phenotypic variance?
Genetic variance + environmental variance.
116
What is the genetic variance consisted of?
Additive variance + non-additive variance.
Additive - genetic variance from the additive effects of alleles.
Non-additive - due to dominance and interactions between genes (ie epistasis).
117
How do you calculate broad sense heritability (H^2)
Genetic variance / Phenotypic variance
0-1
Total proportion due to genes.
118
How do you calculate narrow sense heritability (h^2)
Additive genetic variance / phenotypic variance.
predicts the response to selection.
119
Why is knowing the heritability useful?
Phenotype more accurately refelcts its genotype.
1 - completely controlled by genes.
0 - not controlled by genes at all.
120
Does high heritability mean genetic determination?
| Differences between groups for traits with high heritability are the result of genetic differences.
nooooooo
| Environmental factors can strongly affect traits with a high heritability.
121
What is the quantitative trait locus (QTL)?
A way of measuring genetic complexity, a 1/x shape.
| few genes with large effect at one end, many genes with small effects at the other.
122
What is the common disease - common variant hypothesis?
| Why is this the case?
self explanitory.
late onset don't reduce fitness.
alleles that were advantagous in the past hinder us in the modern society.
123
What can cause linkage disequilibrium?
Natural selection
molecular evolutionary history of population.
SNP and disease causing allele are so close on the chromosome they can't be seperated by crossing over.
Large haplotype blocks not seperated, hot spots for crossing over.
124
What is linkage equilibrium/disequilibrium?
Equilibrium - haplotype present in expected frequencies.
| Disequilibrium - not present in expected frequencies.
