Population Genetics (L19-21)

Question 1

Heterozygosity

Answer 1

frequency of heterozygotes

Question 2

Genotype frequency

Answer 2

number of individuals with genotype/total individuals

So all frequencies add to 1

Question 3

Allele frequency

Answer 3

Number of allele present/total allele

So all allele frequencies add to 1

Question 4

Assumptions of population genetics

x 4

Answer 4

1. diploid organisms
2. Non-overlapping generations
3. Autosomal loci
4. Random mating

Question 5

Hardy Weinberg assumptions - therefore some of the assumptions of population genetics

x 8

Answer 5

1. Random mating
2. No selection
3. No migration
4. No mutation
5. Non-overlapping generations
6. Autosomal locus
7. Infinite population size
8. Diploid organisms

Question 6

Allele lottery

Answer 6

the idea that the allele frequency in next gen under genetic drift is going to be subject to stochastic sampling

Question 7

Homozygosity

Answer 7

The frequency of homozygotes - tending to homozygosity means tending towards all being homozygotes

Question 8

Using effective population size, what is a large population and what is a small population

Answer 8

large is Ne of >10,000

small is <100

Question 9

genetic differentiation

Answer 9

a difference in allele frequency between subpopulations due to genetic drift causing allele frequency divergence

Question 10

Wahlund effect

Answer 10

The deficiency of heterozygotes compared to HWE when summing across subpopulations

Question 11

Fixation index

Answer 11

the proportional difference between expected heterozygosity in the total population and actual heterozygosity in total population

• also known as
  proportion of genetic variance in subpop relative to total pop
• level of inbreeding in subpop compared to total pop

Question 12

Inbreeding

Answer 12

Homozygosity for alleles that are identical - by - descent (idb)

= autozygosity

Question 13

What is F

Answer 13

The inbreeding coefficient = the probability that two randomly drawn alleles are ibd

Question 14

mating system inbreeding

Answer 14

non-random mating among relatives, regardless of population size

Question 15

What does μstand for?

Answer 15

the constant rate of mutation per locus per generation

Question 16

What happens if fitness is random with respect to genotype?

Answer 16

No selection occurs

Question 17

Absolute measurement of fitness

Answer 17

average total number of surviving offspring for a genotype

Question 18

Relative fitness

Answer 18

fitness compared to another genotype - easiest to compare difference in fitness

Question 19

What do we ignore when using relative fitness

Answer 19

changes in population size

Question 20

2 different components of fitness

Answer 20

1. survival to adulthood

2. fecundity

Question 21

What is fecundity

Answer 21

the reproductive output of an individual

• usually the maximum
• combines gamete production and mating sucess

Question 22

what is s

Answer 22

the selection coefficient - or selection differential

Question 23

3 x origins of adaptive alleles

Answer 23

1. new mutation - like melanism in peppered moths or insecticide resistance
2. Standing genetic variation - so already there but was neutral or deleterious - repeatability of evolution with sticklebacks
3. Adaptive introgression

Question 24

What is the major consequence of inbreeding

Answer 24

inbreeding depression

Question 25

what is inbreeding depression

Answer 25

a reduction in fitness of a population due to inbreeding

Question 26

Mating system inbreeding

Answer 26

leads to higher visibility of deleterious alleles to selection - as more homozygote recessive

Question 27

Overdominance

Answer 27

heterozygote advantage

Question 28

2 types of balancing selection

Answer 28

1. Overdominance = rare

2. frequency dependence

Question 29

what is r

Answer 29

the recombination fraction

Question 30

what is the recombination fraction

Answer 30

number of offspring that inherit different alleles of a trait from each parent

Question 31

what is r maximum

Answer 31

0. 5

- when no linkage of alleles

Question 32

what is r<0.5

Answer 32

is r is less than 0.5 then linked loci

Question 33

causes of linkage disequilibrium

x 2

Answer 33

1. gene flow among populations - with different allele frequencies
2. selection for allelic associations - so certain combinations have higher frequency

Question 34

Chromosomal inversions

Answer 34

rearrangement produced by two breakages and inverts the gene on a chromosome

Question 35

Supergene

Answer 35

when multiple gene loci accumulate and are inherited together due to chromosomal inversion

Question 36

what affects the size of the region of neutral variation at linked sites due to directional selection at one locus

Answer 36

the recombination rate near selected locus

Question 37

what is a selective swap

Answer 37

directional selection at a locus causes a loss of neutral variation at linked sites

Question 38

how to escape a local optimum - Wright

Answer 38

recombination
mutation
genetic drift

Question 39

fate of a favourable allele depends on 8 things

what are they?

Answer 39

1. selection differential s
2. initial frequency (especially if allele only now favourable)
3. Population size - determines drift
4. dominance relationships
5. presence of frequency dependence
6. temporal variation in s
7. presence of gene flow with a population where allele absence or not under selection
8. Linkage - to other favourable or unfavourable