11. Genetic DriftDeneti

Genetic drift

random change of allele frequencies from one generation to the next due to random sampling

represernts the '‘background noise’ of eveoultion and the main dirvers of most eveoulnary chage at the genetic level

feretilzation lottery

only one of two alleles of each gene, chosen at random is transmted to each offsrping

other events randomly remove alleles from population (death)

the effects of genetic drift are greater in smaller populations

• the smaller the sample taken, larger the avg deviation from current frequeinces

• drift causes more extreme changed from generation to generation in smaller population

• fization ( when freqeuncy of one alle reaches 100%), also occurs more rapidly in small populations

Importance of population size

drift causes more variable and extreme changes in allele frequency in smaller populations

alleles are fized more rapidly in small populations resulting in a loss of variation

Genetic drift can be magnitfed due to decreases in population size

genetic drift is always acting at some level

drict can be acclerated if the population suddenly decreases

two froms

• founder effect

• bottle neck effect

Founder effect

• occurs when a small number of individuals become isoalted from a larger population

• because founder pop is small, random subset of orgianl population, magnifest the effect of genetic drift

Bottle neck effect

magnifes the ffect of genetic drfit

• a magnfication of the effect of genetic drfit to a reduction in size withing a population

• occurs witin a single poupatlon, rahter then the founding of a new one

Small population = loss of heterozyogisty

carries only a fraction of the orignal genetic diversity (cheetas)

Genetic drift makes veoultion more random and reduces genetic varitaion

• in general and in conlsion genetic drift

• makes eveoulinary process more random

• reduces genetic varation witin population

• result in fization of allesl

• can result in differences between populations