Evolution Without SelectionGenetic Drift: Occurs when a population is so smallthat allele frequencies may be altered by randomchance with no selective pressures. Imagine a beetle population where 40% are green and 60% are brown
Evolution Without SelectionA random catastrophe has reduced the beetlepopulations size.Now 25% are green and 75% are brown.
Evolution Without SelectionIf the last few green beetles fail to pass on theirgreen allele, the allele may be lost forever.
Genetic DriftA certain allele may become extremely common ordisappear entirely.(by chance – recall Punnett squares andprobabilities of passing down traits)
Genetic Drift This results in reduced genetic diversity in the population.The lowworldwidepopulation ofwhite-collaredlemurs hasreduced theirgenetic diversity.
Genetic DriftThere are 2 major reasons for population reductionleading to genetic drift:1) Genetic Bottleneck2) Founder Effect
Think. Pair. Share.Under what circumstances would a small group oforganisms become the foundation of a newpopulation?Where did this small group of organisms comefrom? Consider the terms below.1) Genetic Bottleneck2) Founder Effect
Genetic Bottleneck1) A genetic bottleneck occurs when a speciespopulation is drastically reduced.
Genetic BottleneckThe survivors must reestablish the population usinga very limited gene pool.
Genetic Bottleneck The members of this new population exhibit little genetic variation.This is usually what happens in many endangered species such as the Iberian lynx.
The Founder Effect2) The founder effect occurs when small group froma population moves to a new location.
The Founder EffectThat small group will reproduce to populate the newlocation. Genetic variation will be low.
The Founder EffectOriginalpopulation 3 random animals with this combination of alleles wanders away Alleles of original population
The Founder Effect Animals that moved create a new population in a new location