Population Genetics Flashcards
gene frequency
allele frequency
gametic array
frequency of each type of allele in the population
genotypic array
frequency of each genotype in the population
Hardy-Weinberg Law
allele and genotypic frequency will arrive at and remain at equilibrium frequencies after one generation of random mating if all assumptions are met
What are the assumptions of Hardy-Weinberg
- infinitely large population - random mating - no selection - all are equally fit - no migration - no mutation
panmictic
random mating
Equilibirum equation for Hardy- Weinberg
p^2AA + 2 pqAa + q^2aa
degrees of freedom for Hardy-Weinberg chi2
genotypes - # of alleles
What factors increase genetic variation within populations
mutation migration some types of natural selection
What factors increase genetic variation between populations?
mutation genetic drift some types of natural selection
What factor decrease genetic variation within populations?
genetic drift some types of natural selection
What factors decrease genetic variation between populations?
migration some types of natural selection
mutation
- source of genetic variation - origin of new alleles
pt = 1 - p0*µ = (1-µ)pt-1
Frequency of A in subsequent generations when mutations shift from A to a
q1 = p0µ
frequency of a in subsequent generations when mutations shift from A to a
p1 = (1-µ)pt0 + vq0
frequency of A in subsequent generations when reverse mutation is also occuring with shift form A to a
gametic array in generation 1 when reverse mutation is occurring
[(1-µ)p0 + vq0]A + [(1-v)q0 + µp0]a
migration
change in gene frequency depends on…
- migration rate
- gene frequency of the immigrants
frequency of A allele after migration
p’ = (1-m)p + mP
where…
P = frequency of A on donor population
p = frequency of A on island population
m = proportion of migrants after immigration = immigrants/total now on island
fitness
the ability to survive and reproduce
If no selection, the fitness values…
are 1 for all genotypes
If the a is recessive lethal, aa has a fitness value of…
0
If the heterozygote is the most fit…
it is overdominance
If the heterozygote is least fit…
if is underdominance
directional selection
- favors one extreme
- population mean increases or decreases depending on which extremem is favored
disruptive selection
- advantage for both extremes
- leads toward bimodal population
- underdominance
stabilizing selection
- heterozygotes favored
- decreases variance
- leads to polymorphisms
- overdominance
viability selection
some individuals are more likely to survive to reproduction than others
assortative mating
mate based on phenotype
can be positive or negative
positive assortative mating
mating like individuals together results in simular situations as inbreeding (increased homozygotes but only for loci in mate selection
negative assortative mating
“opposites attract”
keeps diversity in the population
tends to increase the frequency of heterozygous individuals for the loci in mate selection
inbreeding
mating of related individuals
changes frequency of genotypes but not alleles
lead to more homozygous individuals in population over time
affects all loci in the organism
non-random mating changes…
frequency of genotypes but not alleles
equation to account for inbreeding
(p2 + Fpq)AA + 2(1-F)paAa + (q2 + Fpq)aa
How to calculation F
this is the inbreeding coefficient
- calculate the frequency of the alleles
- solve for F based on the modification of the genotypic array due to inbreeding
p2 + Fpq = known frequency
describe the impact of inbreeding
- does not alter allele frequency
- alters genotypic frequencies
- increases both homozygotes
- decreases heterozygote
- eventually everyone will be homozygous and the genotypic array will be pAA + qaa
What are examples of effects of small population size?
random drift/genetic drift
founder effect
inbreeding
What are examples of nonrandom mating
positive assortative mating
negative assortative mating
inbreeding
random drift/genetic drift
random loss and fixation of alleles
sampling error - due to small sampling of alleles in the next generation, only gametes of one type make it into the progeny
founder effect
- small population colonizes new area
- small size makes it likely to undergo genetic drift
- allele frequency in founder may differ from the original population
- they will undergo different, often harsher, selection pressure allowing more rapid change
Bottle neck
a disaster wipes out a large portion of the population
the surviors rebuild but with different allele frequencie
