Flashcards in Lecture 2 - Discontinuous variation and genotype frequencies Deck (20)

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1

## What is the purpose of the Hardy Weinberg equilibrium?

###
-Null model

-For estimating genotype frequencies in a population when given allele frequencies

-based on mendelian genetics

-deviations suggest something interesting is going on

2

## What is discontinuous variation?

### -when a trait shows a limited number of distinct categories e.g. presence/absence of stripes, flower colour

3

## What is the purpose of a null model?

###
Necessary as natural population have varying degrees of genotypes

-for determining whether observed frequencies are unusual in any way and whether an evolutionary process is occuring

4

## What are the features of using punnett sqaures to estimate expected frequencies?

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Relies upon:

-random mating between individuals

-knowing the proportion of alleles in the population

5

## How are allele frequencies symbolised?

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p and q

-always add up to 1

-p+q = 1

6

## How are the frequency of genotypes symbolised?

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fGG

fGg

-Gg

7

## How does the number of alleles relate to the number of individuals?

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In diploid population, individuals have 2 alleles

-N alleles = 2N individuals

8

## What is the equation for working out the expected frequency of p (dominant) allele in hardy Weinberg equilibrium?

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p= ((2N(GG) + N(Gg))/2N

q=p-1

9

## How many degrees of freedom are there for the hardy weinberg test?

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d.f = (# of categories in the data -1) - (# of parameters estimated from the data) e.g.

d.f. = (# phenotypic categories of the data - 1) - (# of allele frequencies estimated from the data)

d.f = (3-1)-1 = 1

estimated number of allele frequencies = 1 as only p needs to be estimated, q is then forced to be 1-p=q

10

## What do deviations from the Hardy Weinberg equilibrium suggest?

###
that assumptions are not fulfilled

Hardy weinberg therefore serves as the null hypothesis to be tested

Normally:

-Mating is not random

-The locus studied is under selection

-There is hidden population structure

-some kind of evolutionary process

11

## What are the assumptions of the Hardy Weinberg equilibrium?

###
-infinite population size

-Diploid organisms

-Random mating

-No mutations

-No selection

-No population structure

-Non-overlapping generations

-Equal allele frequencies among males and females

12

## What occurs in a Hardy Weinbergy equilibrium if the assumptions are fulfilled?

### the allele frequencies in a population remain contant over time

13

## Why is the Hardy Weinberg equilibrium useful if so many unrealistic assumptions need to be fulfilled?

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-describes the behaviour of alleles in 'ideal' populations

-Many populations are in hardy weinberg

-null hypothesis that can be tested

14

## What are the symbols of GG, Gg and gg in hardy weinberg ?

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GG = p2

Gg = 2pq

gg = q2

15

## What is the Hardy-Weinberg equilibrium?

###
1908

-A model that predicts allele and genotype frequencies across future generations if they stay constant

16

## What are the gentype frequences in Hardy Weinberg?

### p1:pq:q2

17

## Why is the Hardy Weinberg equilibrium important?

###
-provides a null model and expectation of what happens if no evoltionary processes are acting

-expectation of what genotype frequencies should be

-can be compared to actual genotype frequences

-if there is a difference suggest some interesting evolutionary processes are happening

18

## How do we know whether observed and expected genotype frequencies are different in hardy weinberg?

### Statistics chi-squared test

19

## What is the formula for the chi-squared test?

###
Chi-squared =

sum of ((observed-expected)^2)/expected))

20