BIO2008: Lecture 5

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  • Created by: LMoney
  • Created on: 10-05-14 20:42
what is expected Heterozygosity? (He)
probability that 2 randomly chosen gametes are different (i.e. heterozygote) (N.B. He is also between 0 and 1)
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what does He equal if HW applies and only 2 alleles?
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how else can He be calculated?
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what are the 2 hierarchical levels of heterozygosity?
within subpopulations: Hs, across all samples (total) HT
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what happens if there is no HW equilibrium?
often expected He does not equal observed (Ho), and generally He > Ho
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when would He not > Ho?
heterozygote advantage and dissassortive mating
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Recap: what could cause there not to be HW?
selection, non-random mating, population structure
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what does the HWE model predict?
genotype frequencies from allele frequencies in random mating populations
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which theory did Sewall Wright come up with?
theory of isolation by distance- F= Wright's fixation index
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how does HWE work?
Reduction average proportion of heterozygotes, relative to expectation under random mating- Use this reduction to estimate the amount of subdivision, i.e. population structure:
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what is F (wright's fixation index) a measure of?
differentiation of populations or regions
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what does Fst indicate?
fixation index of subpopulations relative to total
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how is data often generated now?
PCR polymerase chain reaction
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describe PCR
1) even 1 cell is in theory enough 2) contamination can be problem e.g. human DNA 3) non-invasive techniques 4) many applications, different types of markers
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what is a microsatellite marker?
Repetitive DNA
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what are tandem repeats?
Tandem repeats occur in DNA when a pattern of one or more nucleotides is repeated and the repetitions are directly adjacent to each other
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what is satellite DNA?
Satellite DNA consists of very large arrays of tandemly repeating, non-coding DNA
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which DNA does PCR amplify?
the fragment between primer sites
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describe microsatellites?
1) Many loci in every genome 2) Every locus is highly polymorphic: 5 - 30 alleles 3) A combination of several loci identifies every individual (except identical twins) 4) Generally scored as the length of the fragment amplified
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why are microsatellites highly polymorphic (variable)?
They mutate more frequently
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why do short tandem repeats evolve fast?
1) non-functional: no selection against a mutation 2) many “mistakes” during replication
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what is replication slippage (kind of mutation in micro satellite DNA)?
a form of mutation which leads to either a trinucleotide or dinucleotide expansion or contraction during DNA replication
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what will Fst values tell us about red squirrel populations (for example)?
1) Genetic variation (differentiation) between populations 2) Therefore: Amount of gene flow between populations
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how can dispersal distances be calculated?
by assessing the level of habitat fragmentation that results in populations out of Hardy-Weinberg equilibrium.
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Detection of introductions at wide geographic scale use what?
mitochondrial DNA
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what do Mitochondrial DNA markers tell you about?
Dispersal of female animals
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what does He equal if HW applies and only 2 alleles?



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how else can He be calculated?


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what are the 2 hierarchical levels of heterozygosity?


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what happens if there is no HW equilibrium?


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