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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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

Preview of the front of card 3

Card 4

Front

what are the other Chi-squared tests?

Back

Preview of the front of card 4

Card 5

Front

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

Back

Preview of the front of card 5
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