Changes In Allele Frequencies Over Time

Question 1

What is genetic drift?

Answer 1

stochastic changes in allelic frequency caused by the chance disappearance of alleles when individuals die or fail to reproduce.

Question 2

What is genetic drift?

Answer 2

changes in allele frequencies that are caused directly by changes in population size

Question 3

what is the peppered moth a good example of?

Answer 3

the changes in allele frequency due to traits being determined by a single gene

Question 4

what happened to the peppered moth?

Answer 4

the typical moth was white so that it could be camouflage on silver birches however during the industrial revolution things went black so a single allele which caused black colourings called carbonaria was selected for instead, the numbers of black greatly and quickly increased while the white ones dropped. after. when the clean air act was enforced the white went up again - industrial melanism

Question 5

what was the process that caused moths to go black?

Answer 5

industrial melanism

Question 6

how is the example of the peppered significant?

Answer 6

it shows how allele frequency can be calculated based on the selective advantage that the mutated allele gives

Question 7

what is assumed to be the life cycle when calculating the change of frequency of a single allele?

Answer 7

birth occurs, survives, becomes an adult, reproduces (cycle begins again), dies. the parents don’t out live their young

Question 8

what does the hardy weinberg frequencies show when calculating the change in allele frequencies?

Answer 8

the expected population- the numbers before selection has occurred- at birth how many are present before some have been selected against

Question 9

the survival of offspring depends on what?

Answer 9

their genotype and its relative fitness

Question 10

what would be the relative fitness of the genotypes if CC and Cc were equally likely to survive but cc was selected against?

Answer 10

1:1:1-s

Question 11

what is the definition of relative fitness?

Answer 11

probability of survival relative to reference genotype

Question 12

what does W(genotype) / the mean of W represent?

Answer 12

the probability of survival relative to population average

Question 13

what is the equation for calculating average fitness?

Answer 13

the sum of each genotype frequency multiplied by its relative fitness (relative fitness = fitness divided by average fitness of the population

Question 14

what is the definition of fitness?

Answer 14

how successfully a genotype contributes to the gene pool of the next generation RELATIVE TO THE REFERENCE GENOTYPE (want to know how good you are in the current population)

Question 15

what would a selection coefficient of -1 mean?

Answer 15

all the genotypes with that s die

Question 16

what would a selection coefficient of 0 mean?

Answer 16

it isn’t selected against

Question 17

what is the dominance coefficient?

Answer 17

how dominant one allele is over the other in a heterozygote genotype

Question 18

what is the dominance coefficient? what would values of 0 and 1 mean?

Answer 18

how dominant one allele is over the other in a heterozygote genotype- 0 would mean that A is completely dominant however 1 would mean that takes the full cost of selection as a

Question 19

what is the overall change in allele frequency equation and what does it tell us about the different values relative to rate of change?

Answer 19

the position of s shows us that a change in allele frequency is strongest when s is large (there is a big relative selection pressure)
when the allele frequencies are intermediate and (p x q gives greatest answer when 0.5 x 0.5) therefore when the population is as genetically diverse as possible
for recessive alleles, (h=0) change is greatest when p is large
for dominant alleles (h= 0) then changes occurs mist when p is small - however eventually the curve will plateau because all of the a alleles will be hidden so it is hard to get rid of them
under or over dominance - the het is either better or worse than the two homozygotes- stabilise at very easily because both A and a will be present at an intermediate

Question 20

what are the assumptions in the change of one allele frequency over time model?

Answer 20

this model assumes that
A single population
(can change if Frequencies can change due to migration)
Deterministic dynamics (survival is only influenced by fitness
(can change if Stochastic effects in finite populations)
No mutation
(Frequencies can change due to mutation)
Random fusion of gametes
(Mate choice affects genotype frequencies)
Selection acts on juvenile survival
(Genotypes can affect reproductive success)

Question 21

what does stochasticity mean?

Answer 21

the random perturbations from the predicted allele values due to randomness- such as some individuals not mating, some having more offspring that others, some being randomly killed

Question 22

when does stochasticity have its greatest effect?

Answer 22

in smaller populations when random events are unlikely to be counteracted in other individuals- so large changes in allele frequencies can occur

Question 23

how can genetic drift cause fixation?

Answer 23

random changes in allele frequencies in small populations causes random alleles to become dominant and then fixed

Question 24

what are 2 causes of allele fixation and loss?

Answer 24

genetic drift and selection for advantageous alleles

Question 25

how can unfit genotypes become fixed?

Answer 25

chance in small populations or even by chance

Question 26

what do you expect in a population without selection in terms of allele frequency and how can this not be the case?

Answer 26

you expect no change from p to p+1 however genetic drift can change this

Question 27

what does a loss of diversity coincide with?

Answer 27

a loss of heterozygosity

Question 28

what is an drosophila example of genetic drift?

Answer 28

initially heterozygosity is the majority in populations however over time populations will become fixed for one of the alleles- this can be seen in drosophlia melanogaster in which populations wer shown to be either fixed for bw or bw75after 19 generations

Question 29

how are three ways that you can describe genetic drift?

Answer 29

how similar alleles are within individuals, between individuals (subpopulations) and between populations

Question 30

what are genetic identities?

Answer 30

identities that represent the probability of two alleles being the same- theta, F and alpha

Question 31

what is theta equivalent to and why?

Answer 31

heta= two alleles will be the same so 1-theta= they will be different
expected heterozygosity in HW= chances of picking two different alleles: p and then q, or q and then p so this = 2pq

Question 32

what are the equations for Fis, Fst and …. something else

Answer 32

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