Mechanisms for Evolution

Evolutionary process

Requires :

1. Production of genotypic and phenotypic variations among members of a population

2. Selection for / against those variations passed on to the next generation

Produce Variations

• Mutations

• Gene flow

• Recombination

Reduce Variations

• Genetic Drift

• Natural and Artificial Selection

• Sexual Selection

Mutations

• A change in DNA

• New genes or alleles are produced by mutations

Selective Advantage

A genetic advantage of one organism over it’s competitors

Beneficial mutations

• Relatively rare

• Favored by natural selection

• Accumulate

Harmful mutations

• More common

• Selected against

• No influence

Duplication mutations

• Neutral

• No immediate benefits

• provide raw genetic material

• Source of new genes ; extra copy of gene is free to mutate and may gain a new function

Gene flow

• Movement of alleles from one population to another as a result of migration

• Result : new genes may be introduced into the gene pool → increases variations

Genetic Drift

• Change in frequencies of alleles due to random events in a population

• The smaller the population, the less likely it is that the parent gene pool will be reflected in the next generation

• Reduces variation

Types of Genetic Drift

Bottleneck

• Natural disaster brings a population to near extinction → Very small sample of alleles survive to establish a new population

Founder’s effect

• a small # of individuals colonize a new area → ‘Founders’ carry some but not all of the ‘original’ alleles, rare alleles become more common

Sexual Selection

• Favors the selection of any trait that influences the mating success of the individual

• Can lead to sexual dimorphism : Striking differences between appearance of males and females of the same species

Patterns of Selection

Stabilizing Selection

• The most common phenotypes have higher fitness and become more common

Directional Selection

• Individuals at one end of the phenotype range have higher fitness and become more common

Disruptive Selection

• Individuals at both phenotype extremes have higher fitness and become more common