G19

Question 1

What are the assumptions of the wright fisher model

Answer 1

same as HWE except population is a finite size (N)
generation are non overlapping (adults breed once at the same time and die)
popuation size (N) remains equal through time
equal no. of males and females
no selection
sampling occurs at one point only, the gene pool - 2N gametes are sampled to give N individuals from infinie gamete pool where A occurs within p and a and q frequency

Question 2

at what frequency is an allele then likely to be fixed

Answer 2

0.7

Question 3

whate are the key point about random genetic drift

Answer 3

effects all finite populations, but greater impact on smaller populations
effects are cumulative leading to fixation/loss of alelles in populations (reduce in heterozygosity)
- in population of N individuals 2N aleles of equal fittness

Question 4

at its origin what is the probability of a new alelle being fixed by drift

Answer 4

1/2N

Question 5

what is the probability of fixation equal to at any time

Answer 5

frequency at time t

Question 6

what is the time to fixation

Answer 6

4N

thus quicker to fiaxation in small populations

Question 7

what is the variance in allele frequency equal to after one generation of drift

Answer 7

σ=pq/2N

Question 8

what is a bottle neck

Answer 8

random genetic drift due to a reduction in popualtion size

allele frequencies change, usually rarer alleles are lost

Question 9

give an example of a bottle neck

Answer 9

Achromatopsia - colour blindness caused by recessive mutation of CNGB3 gene
typhoon made population on Pingelap island crash to 30 individuals
so colour blind is now highq

Question 10

what is the founder effect

Answer 10

similiar to bottleneck
dispersal and colonisation by a few migrants, usually rarer alleles lost, higher incidence of some alleles especially if marriage within a closed group

Question 11

give an example of the founder effect

Answer 11

dunkers in Penn. state USA
left germany but remined isolated
have 45% incidence of M blood group compared to 30% in Germnay and 29% in USA
only 13.5% N group compared to 20% adn 21% agian

Question 12

what are the three types of heterozygosity for wrights F statistic

Answer 12

Heterozygosity observed within sub population HI
Heterozygosity expected within sub populations HS
Heterozygosity expected if total population was undivided with random mating HT

Question 13

what is the equation for HI

Answer 13

HI = the sum of BW/(BB+BW+WW)/N 
N= over N sub populations

Question 14

what is the equation of HS

Answer 14

HS = the sum of 2pq/N
N =  over N sub populations

Question 15

What is the equation of HT

Answer 15

2pq of whole population

Question 16

What is FIS

Answer 16

proportional reduction in heterozygotes within sub populations due to inbreeding

FIS = HS -HI /HS

Question 17

what is FST

Answer 17

proportional reduction in heterozygotes in total population assuming random mating due to random genetic drift between sub populations (ie due to subdivision)
FST = HT -HS /HT

Question 18

what is FIT

Answer 18

proportional reduction of heterozygotes in the total population due to inbreeding within subpopulations and to random genetic drift between sub populations
FIT = HT - HI/HT

Question 19

how are the 3 F stats related to each other

Answer 19

(1-FIS)(1-FST)=(1-FIT)

Question 20

what does it mean if FST value is 0

Answer 20

HS=HT
No differentation in allele freq (or no of heterozygotes between sub pops)
all sub pops have same alelle freq as total popualtion

Question 21

what does it meean if FST value is >00.25

Answer 21

very little differentation
moderate differentation 
great differentaion
very great differentiation
HS is declining with increased H number

Question 22

what does it mean if FST value is 1

Answer 22

different alleles fixed in different sub populations at this locus
Hs = 0

Question 23

give an example of physical barriers to gene flow

Answer 23

flighless water striders
allozyme analysis found FST of 0.01 within rivers and FST 0.46 between rivers
high differentiation
no gene flow between as cant fly
however with flying water stiders found no differentiation

Question 24

what F stat can be used when very low rates of gene flow can reduce sub populations differentiating through drift and how else can it be used.

Answer 24

FST = 1/4Nm+1
assumes island model of migration
Nm = no. of immigrants in pop, when m = fraction of individuals that are imigrants
if migration rate known FST can be used as indirect measure of population size.