genetic drift

• change in frequency of alleles in population caused by random chance events influencing survival and reproduction of organisms
• when occurs, alleles that remain unlikely to give individuals possessing them any survival advantage because they have not been naturally selected by environment but present accidently due to random event
• genetic drift has greatest impact on small populations with small gene pool because of further loss of alleles resulting in decrease in genetic variation
• founder effect: genetic drift happens when small group of individuals in population breaks off from larger population to live in distant area and become geographically isolated--> population has low genetic variation
• bottleneck effect: extreme example happening when size of popualtion severly reduced by natrual disasters decimating population killing most individuals and leaving behind small, random assortment of survivors
• such events reduce variation in gene pool of a population resulting in smaller population with low genetic variation remaining to pass on genes to future generations of offpsring through sexual reproduction