Flashcards in G19 Deck (24):

1

## What are the assumptions of the wright fisher model

###
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

2

## at what frequency is an allele then likely to be fixed

### 0.7

3

## whate are the key point about random genetic drift

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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

4

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

### 1/2N

5

## what is the probability of fixation equal to at any time

### frequency at time t

6

## what is the time to fixation

###
4N

thus quicker to fiaxation in small populations

7

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

### σ=pq/2N

8

## what is a bottle neck

###
random genetic drift due to a reduction in popualtion size

allele frequencies change, usually rarer alleles are lost

9

## give an example of a bottle neck

###
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

10

## what is the founder effect

###
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

11

## give an example of the founder effect

###
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

12

## what are the three types of heterozygosity for wrights F statistic

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Heterozygosity observed within sub population HI

Heterozygosity expected within sub populations HS

Heterozygosity expected if total population was undivided with random mating HT

13

## what is the equation for HI

###
HI = the sum of BW/(BB+BW+WW)/N

N= over N sub populations

14

## what is the equation of HS

###
HS = the sum of 2pq/N

N = over N sub populations

15

## What is the equation of HT

### 2pq of whole population

16

## What is FIS

###
proportional reduction in heterozygotes within sub populations due to inbreeding

FIS = HS -HI /HS

17

## what is FST

###
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

18

## what is FIT

###
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

19

## how are the 3 F stats related to each other

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

20

## what does it mean if FST value is 0

###
HS=HT

No differentation in allele freq (or no of heterozygotes between sub pops)

all sub pops have same alelle freq as total popualtion

21

## what does it meean if FST value is >00.25

###
very little differentation

moderate differentation

great differentaion

very great differentiation

HS is declining with increased H number

22

## what does it mean if FST value is 1

###
different alleles fixed in different sub populations at this locus

Hs = 0

23

## give an example of physical barriers to gene flow

###
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

24