Evolution and Gene Frequencies

1. Evolution and Gene Frequencies Chapter 5 Zoology

2. Populations and Gene Pools • Population – group of individuals of the same species occupying a given area at the same time and sharing a common set of genes • Gene Pool – The sum of all alleles for all traits in a sexually reproducing population • 4 ways the gene pool changes: independent Assortment, crossing over, chance fertilization, mutations

3. Most, if not all, Populations are Evolving • Hardy-Weinberg theorem states that evolution stops only when 4 principles are met: • Large population size • No migration in or out • No mutations • Sexual reproduction must be random

4. Four Mechanisms of Evolutionary Change • Genetic Drift - chance events influencing the frequencies of genes • Gene Flow - immigration or emmigration in a population • Mutation - changes in the structure of genes and chromosomes • Natural Selection - certain phenotypes having an environmental advantage over other phenotypes (survival of the fittest)

5. Types of Selection • Disruptive Selection - produces distinct subpopulations • Sexual Selection - mating patterns that produce varying degrees of success of individuals of a population • Stabilizing Selection - narrows the phenotypic range

6. Speciation • Speciation – the formation of a new species (can only occur through reproductive isolation) • Allopatric Speciation – occurs when populations become geographically isolated • Parapatric Speciation – occur in small, local populations (ex. frogs in an isolated pond) • Sympatric Speciation – occurs within a single population (brood parasites)

7. Rates of Evolution • Phyletic Gradualism – slow, continuous change over long period of time (Darwin) • Punctuated Equilibrium – rapid change, followed by periods of stasis, or no change, over long periods of time

8. Molecular Evolution • Using molecular genetics to study base-paring in DNA is a high-tech way of tracking evolution through the genome

9. Mosaic Evolution