Population Genetics

Question 1

What is a breeding population?

Answer 1

a subset of a population which have the potential to breed

Question 2

What is the equation for the frequency of allele A?

Answer 2

p= Number of alleles/2N

Question 3

What does Hardy Weinberg describe?

Answer 3

Hardy Weinberg describes the relationship between allele and genotype frequency in a population where there are no forces acting

Question 4

How much time would it take to reach equilibrium for an autosomal gene?

Answer 4

One generation

Question 5

How will the XY genotype frequency be affected?

Answer 5

the genotype frequency will reflect the allele frequency (in respect to hardy Weinberg)

Question 6

After one generation what will the male allele frequency be the same as?

Answer 6

The allele frequency will be the same as the mother before them

Question 7

What is the allele frequency of a population of sex linked genes at hardy Weinberg equilibrium?

Answer 7

The frequency of an allele will be the weighted mean of the initial frequencies

Question 8

What is W?

Answer 8

W is Darwinian fitness - ie the relative reproductive ability of a genotype

Question 9

What does it mean if W=1

Answer 9

If W=1 this is the genotype producing the most offspring

Question 10

What is S?

Answer 10

S= selection coefficient = intensity of selection against a genotype

Question 11

What is positive directional selection?

Answer 11

positive directional selection is directional selection in favor of replacing one allele with another

Question 12

What is purifying selection?

Answer 12

the selective removal of deleterious alleles.

Question 13

Explain the peppered moth directional selection changes between 1848 and 1900s

Answer 13

Initially dark carbonaria was a rare phenotype seen in peppered moths. In industrial towns, more than 90% of the species adopted this phenotype. It protected them from predators when on soot covered tree trunks. When the clean air act was introduced, it returned to being a rare phenotype

Question 14

What is balancing selection?

Answer 14

Selection to maintain a balanced polymorphism (heterozygote advantage) this is selection against homozygotes.

Question 15

What is an example of heterozygote advantage?

Answer 15

Sickle cell allele Hb-s protects against malaria

Question 16

What is stabilizing selection?

Answer 16

A general term for selection that favors non extreme phenotypes. (usually applies to quantitative characters rather than single gene effects.

Question 17

What is disruptive selection?

Answer 17

Selection that favors both extremes of phenotypes. Plays a role in sympatric speiccation

Question 18

What is an example of frequency dependent selection?

Answer 18

The snail shell morph - a rare shell morph will initially have high fitness as birds wont recognize it as prey - however as frequency increases, rarity decreases and fitness decreases

Question 19

What is Mullerian mimicry?

Answer 19

2 species (eg tasty butterflies) evolve to look the same which is beneficial to both species as commonness of phenotype increases it protects them both (birds learn more are not tasty as there are more)

Question 20

What is Batesian mimicry?

Answer 20

When a species evolves to look like another species which protects it for while, but eventually predators will unlearn that this phenotype is unpleasant and both species are no longer protected

Question 21

What is positive assortative mating?

Answer 21

Individuals “choose” mates who are phenotypically similar to themselves

Question 22

What is the allelic affect of positive assortative mating?

Answer 22

Increases homozygosity in the population for genes affecting the trait looked for in selection

Question 23

What is negative assortative mating?

Answer 23

individuals choose mates unlike themselves

Question 24

What is inbreeding?

Answer 24

Mating between relatives

Question 25

What does the inbreeding coefficient represent?

Answer 25

(F) represents the probability that two alleles in an individual are identical by descent

Question 26

What is a calculation for F that takes into account heterozygosity?

Answer 26

He-Ho/He

Question 27

What is the effect of inbreeding coefficient F on the frequency of heterozygotes in a population compared with Hardy Weinberg?

Answer 27

``` HW = 2pq IB = 2pq - 2pqF ```

Question 28

What number of individuals will carry the homozygous aa genotype in a population of N individuals with inbreeding coefficient F?

Answer 28

q(squared)N + pqFN

Question 29

How might genetic drift affect a special case of inbreeding?

Answer 29

In a local subpopulation of a larger population, random genetic drift might result in fixation (in either direction). This will increase the homozygosity of the allele in the population as a whole.

Question 30

What is the probability that an allele will drift to fixation equal to?

Answer 30

the probability that an allele will drift to fixation is equal to its frequency in the present generation.

Question 31

How is it so that in a Hardy Weinberg population, random genetic drift is not a force acting?

Answer 31

Hardy Weinberg equilibrium assumes the a population is infinitely large, however in reality population size is finite.

Question 32

What is sampling error?

Answer 32

When gametes are passed from the gene pool to the next in a random manner (often leads to change in allele frequencies from one generation to the next)

Question 33

What is the probability of an allele A drifting to fixation?

Answer 33

P^2N

Question 34

What are the two factors determining the fate of an allele in random genetic drift?

Answer 34

Allele frequency and population size

Question 35

How does the effective population size differ from the number of breeding of individuals?

Answer 35

Ne (effective population size) is less than number of breeding individuals (N) if not all individuals have a chance of mating with one another

Question 36

What is the effective population size in a fluctuating population?

Answer 36

The harmonic mean

Question 37

What is a selective sweep?

Answer 37

A reduction in genetic variation in a region of the genome that contains a new advantageous allele A - which is going to fixation. This happens via hitchhiking

Question 38

What is a population bottleneck and what genetic phenomenon do they show?

Answer 38

A temporary reduction in population size, which shows strong genetic drift