Population Genetics TB

Question 1

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

Answer 1

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

Question 2

equation for frequency of an allele

Answer 2

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

Question 3

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

Answer 3

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
a diploid population of N individuals will have 2N alleles

Question 4

equation for frequency of an allele when given genotype frequencies only

Answer 4

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

Question 5

calculating allele frequencies for x linked loci concepts

Answer 5

females can either be homozygous or heterozygous, males are hemizygous

Question 6

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

Answer 6

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

Question 7

calculating frequency of x linked alleles from genotypic frequencies

Answer 7

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

Question 8

Hardy weinberg principle

Answer 8

Two alleles in a diploid individual are randomly and independently
sampled from an infinitely large pool of gametes
Probability of sampling the A allele is p
Probability of sampling the a allele is 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

Question 9

hardy weinberg assumptions

Answer 9

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

Question 10

mendel’s principle of segregation

Answer 10

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

Question 11

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….

Answer 11

p^2 2pq and q^2

Question 12

what does random mating mean

Answer 12

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

Question 13

implications of hardy weinberg principle

Answer 13

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

Question 14

positive assortative mating

Answer 14

tendency for like individuals to mate

Question 15

negative assortative mating

Answer 15

tendency for unlike individuals to mate

Question 16

what type of assortative is inbreeding

Answer 16

positive assortative mating for relatedness

Question 17

how does inbreeding differ from other types of assortative mating

Answer 17

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

Question 18

effect of inbreeding on the population

Answer 18

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

Question 19

outcrossing

Answer 19

preferential mating between unrelated individuals

Question 20

what is meant by homozygous alleles being in the same state

Answer 20

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

Question 21

what is meant by homozygous alleles being identical by descent

Answer 21

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

Question 22

inbreeding coefficient

Answer 22

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

Question 23

changes in alleles with inbreeding

Answer 23

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

Question 24

self fertilisation effects on allelic proportions

Answer 24

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

Question 25

inbreeding depression

Answer 25

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

Question 26

how can inbreeding be favoured

Answer 26

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

Question 27

processes that bring about changes in allele frequencies

Answer 27

mutation migration genetic drift natural selection

Question 28

genetic drift

Answer 28

random effects due to small population size

Question 29

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

Answer 29

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

Question 30

how is an equilibrium of mutation reached

Answer 30

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

Question 31

equation for change in q frequency due to reverse mutation

Answer 31

mutation rate of reverse mutation x q

Question 32

equation for overall change in allelic frequencies

Answer 32

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

Question 33

equation for allelic frequency at equilibrium

Answer 33

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

Question 34

what allelic equilibrium means

Answer 34

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

Question 35

migration: definition and 2 effects

Answer 35

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

Question 36

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

Answer 36

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

Question 37

equation for change in allelic frequency due to migration

Answer 37

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

Question 38

effect of migration over time

Answer 38

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

Question 39

how genetic drift opposes hardy weinberg principle

Answer 39

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

Question 40

variance (s^2)

Answer 40

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

Question 41

effective population size

Answer 41

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

Question 42

causes of genetic drift

Answer 42

sampling error reduction in population size founder effect genetic bottleneck

Question 43

effects of genetic drift

Answer 43

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

Question 44

fixation (genetic drift)

Answer 44

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

Question 45

natural selection

Answer 45

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

Question 46

fitness (W)

Answer 46

relative reproductive success of a genotype 0-1

Question 47

fitness calculation

Answer 47

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

Question 48

selection coefficient (s)

Answer 48

relative intensity of selection against a genotype 1-W

Question 49

general selection model

Question 50

overdominance

Answer 50

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

Question 51

underdominance

Answer 51

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