# BIO2008: Lecture 2

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- Created by: LMoney
- Created on: 10-05-14 18:42

what is the probability of an allele equal to?

its frequency

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what does Mendel's law state?

Segregation of alleles of a gene in formation of reproductive cells

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How can you test whether genotypic ratios in offspring follow Mendelian inheritance?

Chi-squared test (X^2 test)- in this case Chi-squared goodness of fit because testing against distribution

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what are the other Chi-squared tests?

Chi squared test of association, Chi squared test of homogeneity

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should frequencies or number be used in chi-squared tests?

always numbers

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A dominant over a. In offspring of a Aa x Aa cross what is the probability of phenotype A?

75%

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what is the most common mode of variation at the DNA level?

mostly codominant

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what are the most widely used molecular markers in population genetics?

allozymes (isozymes, protein variants)

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which DNA based methods are used in population genetics?

1) RFLP analysis 2) PCR 3) sequencing

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how is Allozyme or DNA analysis carried out?

Run an extract/PCR product of individuals on a gel: separate molecules on charge- measure differences in velocity in the gel

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what is the Hardy Weinburg principle used for?

calculate expected genotype frequencies under 'random' mating in 'ideal' population

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what is an ideal population?

diploid, sexual reproduction, nonoverlapping, generations, large populations, no effect of natural selection etc.

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Let p be the allele frequency of A and q the allele frequency of a, what are the frequencies for the genotypes?

p^2 for AA, 2pq for Aa, q^2 for aa

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What is the maximum frequency of heterozygotes in a population? (according to Hardy Weinburg)

50%

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what is the test for presence of HW equilibrium?

Chi squared goodness of fit test

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what does the Chi squared goodness of fit test do, in this context?

Tests whether there is a significant difference between genotype numbers observed and genotype numbers expected under HW

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how many degrees of freedom is there for 3 genotypic classes?

1

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If the calculated chi-square value is less than the 0 .05 value in the table, what do we do with the hypothesis?

we accept it, if it was greater- accept it- if we accept, means the population is in HW equilibrium

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when can examples of the HW principle become more complicated?

1) If sex-linked (gene is on X chromosome) 2) If dominant/recessive alleles 3) If more than two alleles 4) If you have polyploids (too complicated)

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when can deviations from HW happen?

1) Inbreeding 2) Population structure 3) Mate choice 4) Selection against/for certain genotype

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when does inbreeding happen?

1) Plants that self-fertilise 2) Mating between related individuals

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what happens to the genotype frequencies with inbreeding?

Excess homozygote genotypes relative to the frequencies expected with random mating

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what halves number of heterozygotes every generation?

self-fertilisation

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what lowers proportion heterozygotes in subpopulations, relative to expected?

structure

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what is assortative mating, or positive assortative mating?

similar individuals mate more often than expected under random mating

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what is disassortative mating or negative assortative mating?

dissimilar individuals mate more often than expected under random mating

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What do you predict with assortative mating?

Less heterozygotes than in HW (deficit)

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what is an example of assertive mating?

flowering time differences

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what are examples of disassortive mating?

SI system in plants, MHC in mammals

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selection with heterozygote advantage you predict to find what?

More heterozygotes than expected

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with Hybridisation, often heterozygotes less fit so you would predict to find what?

Deficit heterozygotes, less

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## Other cards in this set

### Card 2

#### Front

what does Mendel's law state?

#### Back

Segregation of alleles of a gene in formation of reproductive cells

### Card 3

#### Front

How can you test whether genotypic ratios in offspring follow Mendelian inheritance?

#### Back

### Card 4

#### Front

what are the other Chi-squared tests?

#### Back

### Card 5

#### Front

should frequencies or number be used in chi-squared tests?

#### Back

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