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SL12003 Genetics > Population Genetics > Flashcards

Population Genetics Flashcards

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1
Q

equation for frequency of a genotype in a population, for example of AA

A

f(AA)=number of AA individuals/N where N is the total number of individuals within the population

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2
Q

equation for frequency of an allele

A

number of copes of the allele/number of copies of all alleles at the locus

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3
Q

equation for frequency of an allele in a population in which there are only 2 alleles for the gene/locus

A

p=f(A)=2nAA+nAa/2N
q=f(a)=2naa+nAa/2N
where N is the total number of individuals in the sample and n is the number of individuals with those alleles

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4
Q

equation for frequency of an allele when given genotype frequencies only

A

p=f(A)=f(AA)+1/2f(Aa)

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5
Q

calculating allele frequencies for x linked loci concepts

A

females can either be homozygous or heterozygous, males are hemizygous

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6
Q

equation for allele frequencies for x linked loci from number of individuals with the genotypes

A

p=f(XA)=2nXAXA+nXAXa+nXAY/2nfem+nmale

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7
Q

calculating frequency of x linked alleles from genotypic frequencies

A

p=f(XA)=f(XAXA)+1/2f(XAXa)+f(XAY)

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8
Q

Hardy weinberg principle

A

under certain conditions allelic frequencies of a population dont change and the genotypic frequencies stabilise after one generation in the proportions p^2, 2pq and q^2. in these proportions, the population is said to be in hardy weinberg equilibrium

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9
Q

hardy weinberg assumptions

A

large population
random mating
not affected by mutation
no migration
no natural selection
applies to a single locus

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10
Q

mendel’s principle of segregation

A

each individual organism possesses two alleles at a locus and each has an equal probability of passing into a gamete. frequencies of alleles in gametes=frequency of alleles in parents

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11
Q

if the frequencies of alleles in a randomly mating population are p and q then the frequencies of the genotypes in the next generation will be….

A

p^2 2pq and q^2

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12
Q

what does random mating mean

A

members of the population mate randomly with respect to genotype-each genotype mates relative to its frequency.

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13
Q

implications of hardy weinberg principle

A

reproduction alone doesnt cause evolution
genotypic frequencies are determined by the allelic frequencies

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14
Q

positive assortative mating

A

tendency for like individuals to mate

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15
Q

negative assortative mating

A

tendency for unlike individuals to mate

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16
Q

what type of assortative is inbreeding

A

positive assortative mating for relatedness

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17
Q

how does inbreeding differ from other types of assortative mating

A

it affects all genes, not just those that determine the trait for which the mating preference exists

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18
Q

effect of inbreeding on the population

A

increase in the proportion of homozygotes and a decrease in the proportion of heterozygotes
deviation from the hardy weinberg equilibrium frequencies of p^2, 2pq and q^2

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19
Q

outcrossing

A

preferential mating between unrelated individuals

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20
Q

what is meant by homozygous alleles being in the same state

A

the two alleles are like in structure and function but do not have a common origin

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21
Q

what is meant by homozygous alleles being identical by descent

A

the copies are descended from a single alleles that was present in an ancestor

22
Q

inbreeding coefficient

A

F, 0-1
measure of the probability that two alleles are identical by descent

23
Q

changes in alleles with inbreeding

A

f(AA)=p^2+Fpq
f(Aa)=2pq-2Fpq
f(aa)=q^2+Fpq
because the proportion of heterozygotes decreases by 2Fpq and half of this value (Fpq) is added to the proportion of each homozygote each generation

24
Q

self fertilisation effects on allelic proportions

A

reduces proportion of heterozygotes by 1/2 each generation until all are homozygotes

25
Q

inbreeding depression

A

decreased fitness arising from inbreeding due to the increased appearance of lethal/deleterious traits

26
Q

how can inbreeding be favoured

A

helps preserve groups of genes (co-adapted gene complexes) that exhibit gene interaction and work well together in a specific environment (whereas outcrossing causes recombination)
can cause homozygotes that are beneficial as lethal alleles removed by natural selection

27
Q

processes that bring about changes in allele frequencies

A

mutation
migration
genetic drift
natural selection

28
Q

genetic drift

A

random effects due to small population size

29
Q

equation for change in an allele’s frequency due to forward mutation

A

change in q=rate of forward mutation x frequency of p

30
Q

how is an equilibrium of mutation reached

A

more alleles of p means rate of forward mutation faster. increases q so more reverse mutations until equilibrium reached

31
Q

equation for change in q frequency due to reverse mutation

A

mutation rate of reverse mutation x q

32
Q

equation for overall change in allelic frequencies

A

change in q = (rate of forward mutation x p) - (rate of reverse mutation x q)

33
Q

equation for allelic frequency at equilibrium

A

rate of forward mutation/(rate of forward mutation + rate of backwards mutation)

34
Q

what allelic equilibrium means

A

no net change in allele frequency
genotypic frequencies also remain the same
takes a long time to reach equilibrium as mutation rates low

35
Q

migration: definition and 2 effects

A

movement of genes from one population to another (gene flow)
1. prevents populations becoming genetically different
2. increases genetic variation

36
Q

equation for frequency of allele a in merged population once unidirectional migration has occurred

A

frequency = frequency of a in migrant population + frequency of a in resident population

37
Q

equation for change in allelic frequency due to migration

A

amount of migration ( frequency of a in migrant pop - freq a in resident pop)

38
Q

effect of migration over time

A

equilibrium reached where even though migration still occurs, the allelic frequencies are equal in the migrant and resident populations
gene pools of the two populations are now the same
keeps populations homogenous in allelic frequencies (counteracts effects of genetic drift and natural selection)
increase in genetic variation as mutations spread to new population

39
Q

how genetic drift opposes hardy weinberg principle

A

composition of gametes deviates from gene pool of parents, more significant in smaller gametic samples
non-random mating
sampling error

40
Q

variance (s^2)

A

measures genetic drift
pq/2N
genetic drift is maximal when p and q are equal and is greater when N is smaller

41
Q

effective population size

A

number of breeding adults
influenced by sex ratio, fluctuations in population size, age structure of population, random mating and variation in individuals in number of offspring produced

42
Q

causes of genetic drift

A

sampling error
reduction in population size
founder effect
genetic bottleneck

43
Q

effects of genetic drift

A

change in allele frequencies
reduction in genetic variation-increase in homozygous

44
Q

fixation (genetic drift)

A

when one allele has a frequency of 1 in a population so all individuals are homozygous for one allele
alleles with an initial higher frequency are more likely to become fixed
different populations diverge genetically from each other over time-genetic drift is random so different populations acquire different changes in frequencies. all populations reach fixation, but with different alleles

45
Q

natural selection

A

differential reproduction of genotypes
individuals with an adaptive trait produce more offspring

46
Q

fitness (W)

A

relative reproductive success of a genotype
0-1

47
Q

fitness calculation

A

mean number of offspring produced by a genotype/mean number of offspring produced by most prolific genotype

48
Q

selection coefficient (s)

A

relative intensity of selection against a genotype
1-W

49
Q

general selection model

A
50
Q

overdominance

A

selection in which the heterozygote has higher fitness than either homozygote
stable equilibrium is reached

51
Q

underdominance

A

heterozygote has lower fitness than the homozygotes
unstable equilibrium reached
any disturbance will cause one allele to become fixed

52
Q
A

SL12003 Genetics (11 decks)

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