Module #3 | Lecture #5: Genetic Divergence

Evolutionary process

1. Variation

2. Natural Selection

3. Genetic Divergence

4. Reproductive Isolation

5. Speciation

Gene Flow

The physical movement of alleles into and out of population through immigration and emigration

• flow tends to counter genetic differences

• can slow a population from fully adapting to new environments

• common way to introduce new allele to a population

  • ex: humans, blue jays

Genetic drift

The random change in allele frequency over the generations, brought about by chance

• changes in frequency regardless of fitness of individuals

• Either favors then elimination or fixation of an allele ( 0% or 100%)

• Tends to reduce genetic variation and leads to the homozygous condition

In the absence of gene flow, natural selection will alter allele frequencies in different ways due to genetic drift

Sampling Error

The smaller the sample size, the greater the chance of deviation from predicted results

Sampling error in natural populations

Deviation from expected results because real populations are finite in size

Bottleneck Effect

A severe reduction in population size brought about by intense selection pressure or natural disaster

ex: contagious disease, habitat loss, hunting, etc.

Issues with the bottleneck effect

1. Survivors gene pool may no longer represent the original population

2. By chance certain alleles may be over represented, under represented or eliminated

3. Genetic drift may continue to alter the gene pool and reduce variation when the population size is small

Examples of genetic divergence

Elephant seals (severe hunting), cheetahs (monomorphic for many genes)

Founders Effect

When a few individuals become isolated from a larger pop.

1. Occurs when a few members migrate to a new habitat

2. Isolated gene pool may no longer represent the original population

Genetic Divergence

Any structural, functional, or behavioral difference that favors reproductive isolation is a by product of genetic change

1. Genetic changes between populations can be countered by gene flow

2. Barriers prevent the exchange of genes between populations and leads to evolutionary divergence of each population

   1. Leads to difference between gene pools of the separate population