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
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.
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.
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
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
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
Reasons for deviating from random mating (2)
- 1. Deviations due to phenotypic resemblance.
- 2. Deviations due to genetic relatedness.
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
Autozygosity vs allozygosity
- 2. autozygosity: two alleles that are identical by descent.
- 3. allozygosity: two alleles that are NOT identical by descent
Def. inbreeding coefficient (F)
- the probability that the two alleles in an individual
- at a given gene are identical by descent (= probability of autozygosity.)
def: Population genetics
study of how genes, alleles, and chromosomes behave in populations
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).
What is the ultimate effect of Mutation on a pop? (2 answers)
- 1.) change in allelic frequency
- 2.) Evolution
- (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
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
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
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