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MBB262 > Population Genetics > Flashcards

Population Genetics Flashcards

1
Q

What is a breeding population?

A

a subset of a population which have the potential to breed

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2
Q

What is the equation for the frequency of allele A?

A

p= Number of alleles/2N

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3
Q

What does Hardy Weinberg describe?

A

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

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4
Q

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

A

One generation

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5
Q

How will the XY genotype frequency be affected?

A

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

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6
Q

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

A

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

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7
Q

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

A

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

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8
Q

What is W?

A

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

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9
Q

What does it mean if W=1

A

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

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10
Q

What is S?

A

S= selection coefficient = intensity of selection against a genotype

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11
Q

What is positive directional selection?

A

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

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12
Q

What is purifying selection?

A

the selective removal of deleterious alleles.

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13
Q

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

A

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

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14
Q

What is balancing selection?

A

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

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15
Q

What is an example of heterozygote advantage?

A

Sickle cell allele Hb-s protects against malaria

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16
Q

What is stabilizing selection?

A

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

17
Q

What is disruptive selection?

A

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

18
Q

What is an example of frequency dependent selection?

A

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

19
Q

What is Mullerian mimicry?

A

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)

20
Q

What is Batesian mimicry?

A

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

21
Q

What is positive assortative mating?

A

Individuals “choose” mates who are phenotypically similar to themselves

22
Q

What is the allelic affect of positive assortative mating?

A

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

23
Q

What is negative assortative mating?

A

individuals choose mates unlike themselves

24
Q

What is inbreeding?

A

Mating between relatives

25
Q

What does the inbreeding coefficient represent?

A

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

26
Q

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

A

He-Ho/He

27
Q

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

A 
HW = 2pq
IB = 2pq - 2pqF
28
Q

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

A

q(squared)N + pqFN

29
Q

How might genetic drift affect a special case of inbreeding?

A

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.

30
Q

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

A

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

31
Q

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

A

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

32
Q

What is sampling error?

A

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)

33
Q

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

A

P^2N

34
Q

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

A

Allele frequency and population size

35
Q

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

A

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

36
Q

What is the effective population size in a fluctuating population?

A

The harmonic mean

37
Q

What is a selective sweep?

A

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

38
Q

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

A

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

MBB262 (7 decks)

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