Genetic Drift,
Founder Effect,
Bottleneck
Effect.
Genetic Drift
• Is a change in the allele frequencies of a
population as a result of chance processes.
• It happens in small populations where chance
alone can play a considerable role.
• Heterozygous gene pairs tend to become
homozygous for one allele by chance rather
than selection, so that the alternative can be
lost.
Founder Effect
• If a few organisms move to a new area, they
may only possess a few of the available genes
from the original population.
• Because they only have some of the available
alleles from the ‘gene pool’ of the ‘founder
ancestors’ the new population can have
different genes from the same species
elsewhere.
The Founder Effect
The Bottleneck Effect
• Disasters such as fires or drought can reduce a
population down to just a few individuals.
• These individuals may not necessarily be
representative of the original population.
• Some alleles will be above the normal number
and some may be lost forever.
• If one survivor has a rare gene, the new
population may no longer be rare!
The Bottlenect Effect
Questions
• Genetic Drift
– Questions in Booklet .
• (Answers in the back of Patterns of Life Workbook)
• Page 346 BIOZONE
– The Founder Effect
• Page 344 BIOZONE
– The Bottleneck Effect
• Page 345 BIOZONE