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H-W assumptions and Predictions + special note
- Assumptions - pop is large, randomly mating, not affected by mutation, migration, or natural selection
- Predictions - allelic fq dont change
- Predictions -
genotypic fq stabalize after one generation of p2 2pq and q2 Special note = assumptions only apply to single locus
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Why does H-W law work
Alleles of parents segregate independantly (mendelian genetics) therefore the fq of alleles in gametes will be the same as in parents.
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What does H-W Law state (3 things)
- 1.) reproduction alone will not cause evolution
- 2.) When a pop us in HWE - genotypic fq are determined by allelic fq
- 3.) Single generation of random mating produces equilibrium fq.
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How to apply HW (what does this mean and 3 steps involved)
- Must compare expected genotypic frequencies to observerd fq's
- 1.) determine allelic fq2.) find expected genotypic fq by squaring allelic frequencies
- 3.) compare expected vs observed using chi sq test
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What are p and q for allelic fq and genotypic fq
What is Genotype fq
- P and Q represent allele frequencies ie p=f(A) q=f(a)
- Genotype frequency is (p+q)2 = p2 + 2pq + q2 = 1
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Two types of non-random mating due to phenotypic resemblence
- Positive assortative mating = tendency for like individuals to mate ie humans and height tall with tall... or inbreeding (different because affects all genes, not just determinate of trait of preference)
- Increases homozygosity
- Negative assortative mating = tendency for unlike individuals to mate ie tall with short... increases heterozygosity
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Reasons for deviating from random mating (2)
- 1. Deviations due to phenotypic resemblance.
- 2. Deviations due to genetic relatedness.
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Two types of non-random mating due to genetic relatedness
- 1.) Inbreeding - creates increase in homozygous and decrease in heterozygous2.) Outbreeding - avoidance of mating with related individuals (increases heterozygosity of pop)
- 3.) Genotypic fq change, allele fq do not
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Autozygosity vs allozygosity
- 2. autozygosity: two alleles that are identical by descent.
- 3. allozygosity: two alleles that are NOT identical by descent
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Def. inbreeding coefficient (F)
- the probability that the two alleles in an individual
- at a given gene are identical by descent (= probability of autozygosity.)
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def: Population genetics
study of how genes, alleles, and chromosomes behave in populations
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Half-sb vs Full-sip mating pathway
- Pedigrees that begin with a half-sib mating have one loop (pathway).
- Pedigrees that begin with a full-sib mating contain 2 loops (2 pathways).
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What is the ultimate effect of Mutation on a pop? (2 answers)
- 1.) change in allelic frequency
- 2.) Evolution
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(delta)q= ?
- (mu)p-(v)p; where (mu) is forward mutation rate and (v) is reverse mutation rate
- as p --> q, (delta)q decreases because there are less
- p->q
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allelic frequency equilibrium is def as? (for p and q)
- q= (mu)/((mu)+(v))p = (v)/((mu)+(v))
- def only by forward and reverse rates (not starting fq)
- genotypic fq stays same because in HW equilibrium
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What is Pt and how do you calculate it? (forward mutation model)
Pt is the allelic frequency after (t) generations experiencing mutation at rate (mu)
Pt = P0(1-(mu))t
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Migration effects (2) + similarities to Mutation
- 1.) Prevents pop from becoming genetically unique (pop become more similiar) "great homogenizer"
- 2.) Increase genetic variation with in a pop.
1.) Both bring genetic variation to a pop, but migration is much faster
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