Studying evolution in small populations Life is a fine balance between shared commonalities and amazing diversity.

Factors that cause Changes in allele frequency  1. Natural Selection  2. Gene Flow  3. Mutations  4. Genetic Drift(affects only small populations

Genetic Drift  Changes that happen to small populations Random chance Random chance Shifts allele frequencies Shifts allele frequencies  Chance only affects small populations Ex. Think about tossing a coin ten times Ex. Think about tossing a coin ten times First trial 3 heads: 7 tailsFirst trial 3 heads: 7 tails 2 nd trial 6 heads: 4 tails2 nd trial 6 heads: 4 tails 3 rd trial 5 heads: 5 tails3 rd trial 5 heads: 5 tails

Imagine the start of a new population  Imagine a small group migrates to a new area  Start new population  New populations are usually very small to begin with

Founder effect  Any influences that affect the new population  Few organisms start population Different from mainland where they migrated from Different from mainland where they migrated from

Example  The nene goose Descendants of the Canada goose Descendants of the Canada goose Less webbed toes, sharper to climb lava Less webbed toes, sharper to climb lava Rarely need to fly Rarely need to fly  1778, around 25,000 nene geese left  Down to 30 by 1950  Now there are Sound

Inbreeding  In small populations, individuals tend to start to become too similar  No choice but to mate with close relatives  Loss of genetic variation  If only 2 individuals per generation, Comletely homozygous after only 20 generations Comletely homozygous after only 20 generations

Reason for Inbreeding  Populations can hit a bottleneck a drastic reduction in number a drastic reduction in number  Ex. American bison Severe population bottleneck in 19 th century Severe population bottleneck in 19 th century Because of hunting Because of hunting

Inbreeding depression  Bad Effects of Inbreeding Existence of harmful recessive alleles Existence of harmful recessive alleles Inbreeding increases homozygosity Inbreeding increases homozygosity  Reduced fertility and survival compared to large populations

Zoos  Have very small populations of animals Set up to preserve animals Set up to preserve animals Promote awareness of animals Promote awareness of animals Are prone to inbreeding Are prone to inbreeding  Breeders often arrange matings between distantly related animals