Population genetics Flashcards
(45 cards)
species
a discrete, reproductively defined system of populations with a common evolution
population
a group of animals of one species which interbreed (particular area)
gene pool
set of genes and/or alleles in the entire population
breed
a population distinguishable from another of the same species by frequencies of genes, chromosomal variation, or hereditary phenotypic characteristics
population genetics
allele frequencies of a population of animal
-ig what is the frequency of the polled allele in french, canadian, world wide charolais
what does it mean if genes are fixed
in some species some genes are fixed meaning all animals are homozygous for the same allele
hardy-weinberg equilibrium
p+q=1
p=the proportion of the dominant allele
q=the proportion of the recessive allele
1AA : 2Aa : 1aa in pq
p^2 : 2pq : q^2
hardy-weinberg eq allele frequencies
-q^2=fq of autosomal res
-q=vq^2=frequency of recessive allele
-1-q=p=frequency of dominant allele not that frequency of individuals with dominant phenotype is p^2+2pq (not just p^2)
-q^2 = frequency of individuals with recessive genotype
if you have the frequency of autosomal recessive homozygote how do you get the frequency of recessive alleles
q=square root of q^2
-ie. if 35% of the canadian charolais are horned (recessive to polled) what is the gene frequency of the horned allele q^2=0.35 q= square root 0.35=0.59 so freq of horned allele is 59
on a gene frequency graph what are the trends youd see
-homozygote increases exponentially with gene frequency
-heterozygotes dont exceed 50%
-rare alleles occur predominantly in heterozygots
for the hardy-weinberg eq gene frequencies stay stable if:
-mating is random
-no selection
-no mutation
-large population
domestic animal breeding and hardy-weinberg
-humans select which animals to breed
-wild choose them self
-hardy-weinberg eq equation works well for wild animals but must be domesticated for wild animals
-in domestic animals without random breeding we must modify calculations of gene frequency, if phenotypic selection is used
-ie. if we want to fix polled in a charolais herd
snyders ratio
-based on phenotype i.e. rarely know genotype of animals for dominant trait
-used to determine proportion of recessive or dominant offspring per parental mating type
snyders ratio for dominant x dominant
-parents could be:
-Dd X Dd=2pq x 2pq
-DD x Dd=p^2 x 2pq
-DD x DD=p^2 x p^2
-only Dd x Dd produce dd offspring therefore 1/4 dd of (2pq x 2pq)
-=1/4 dd
snyders ratio
-recessive phenotype offspring/total from dominant x dominant
-=(q/1+q)^2
what is snyders ratio based off
-phenotype (rarely know genotype of animal for dominant trait
snyders ratio for dominat x dominant
dom 1-(q/1+q)^2
res (q/1+q)^2
syders ratio for dominant x recessive
dom 1-(q/1+q)
res (q/1+q)
syders ratio for rec x rec
dom: 0
rec: 1
for dominant x rec what could parents be
Dd X dd=p^2 x q^2
DD x DD=2pqxq^2
genetic drift
-small subpopulations become increasingly different over generations
-e.g. rabbit population
-p and q freq changes in each generation
-by chance the q allele is lost by 3rd generation
effects of population size on genetic drift
-pop size influences the allele frequency changes or “drift”
-fluctuates more in smaller populations
founder effect
-founding population (herd) is small
-wild: gene frequency changes are due to chance
