B.7F Evolutionary Mechanisms

Student Expectation

The student is expected to analyze and evaluate the effects of other evolutionary mechanisms, including genetic drift, gene flow, mutation and recombination.

Key Concepts

• There are five mechanisms of biological evolution: natural selection, genetic drift, gene flow, mutation, and recombination. Each of the mechanisms of evolution either increases or decreases the genetic diversity within and among populations.
• Genetic drift is the change in gene frequencies due to chance. Genetic drift is much stronger in smaller populations than in larger ones. Genetic drift can increase or decrease diversity; but it cannot create genetic variation, it can only destroy it.
• Gene flow is the movement of alleles between populations. It reduces the genetic diversity between populations, but increases the genetic diversity within populations by introducing new genes.
• Mutations are changes in genes that occur within a single individual. They are the raw materials for evolutionary change because natural selection favors beneficial mutations, increasing their frequencies, and eliminates harmful ones. The vast majority of mutations are either neutral, with no effect on fitness, or deleterious (harmful).
• Recombination occurs during sexual reproduction and via other mechanisms in asexual organisms. It results in new combinations of alleles and vastly increases the diversity of genotypes in each generation. Because most alleles segregate independently and randomly during meiosis, sexual organisms are able to generate millions of new allele combinations in their gametes.

Fundamental Questions

• What are the five mechanisms of biological evolution and how do these mechanisms change diversity of populations?
• Why are mutations the raw materials for natural selection?
• How does recombination increase genetic variation?