Population genetics Flashcards
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
founder effect example: SCID arabians
-severe combined immuodeficency
-autosomal recessive (cc)
-in england: q^2=0.01 or 1% of arabs
-q=1
-australia: 2 stallions from england purchased
-both carriers: Cc
-q=0.5
-17/204=8.3% affected foals born
breed introduction
-example of founder effect
-“exotic” cattle to canada
-holstein to canada
-llamas to cali
-relatively small # of animals “found” the population
-“new” population could be very different form parent population in terms of gene frequency
closed herd example
-swine companies such as:
-HyPor
-founded their canadian branch with 1 shipment of british stock
population bottle neck
-example of genetic drift
-population is severely reduced in numbers for 1 or more generations
-decrease can be caused by a natural desaster
-start w good mix—> more of one then the other
show ring and AI impacts
-promotes “few” select sires
-these are used extensively
-i.e disproportionally
-20 years ago: 1 salers bull was present in >70% of pedigrees
panmictic populations
-random matings in breeding population
-exchange of breeding animals
gene flow
-exchange of new alleles between subpopulations
-panmictic populations
-genetic isolates
gene isolates
-subpopulation breeds only within itself
-“closed” herd
cline
-phenotypic gradients across a geographical region
-gene flow is greatest between adjacent populations
migration
-migration of wild animals could be from their own movement
-in domestic animals, migration can include: purchase, trucking to new barn, ranch, etc…
gene flow implies migration therefore…
gene frequencies change
-typically, the small population (“island”) recives immigrant animals from the large population (“mainland”)
how is migration different in wild animals vs domestic
-for wild animals it is typically some males and some females
-migration in domestic animals is usually buying a few new males
what can import and export regulations do to migration
-can halt migration
what does gene flow (migration) allow for
assure a constant source of genetic variation
-retards randome drift
-allows spread of new neg or pos mutation
how do domestic animals breeds vs presarvationists differ
-domestic animal breeders want change
-perservationists want no change
hardy-weingberd eq mating is random
-assortative mating
-pos: means both mates have “same” trait
neg: means the two mates do not have the “same” trait
-AI
-showring winners
dominance hirrachy in animals
-older or dominant male mates mots females
assortative mating affects co-dominant alleles (not breeding like to like)
-horses
-mating two opposite homozygotes to accive the heterozygote
-sorrel x cremello–> palomino
hardy weinburg eq no migration examples for domestic animals
-cattle purchase new bulls (keep heifer replacements)
-horses (stables may be founded by one stallion, but buy mares)
-poultry (total in-total out)
-pigs (both sexes burchased)
hardy weinburg eq no mutation
mu=mutation rate
-normally very low (we arent trying to mutate)
-no attempt to increase this (can come up and be good)
hardy werinburg a large population
