Evolution and Gene Frequencies

Chapter 5

Zoology

Populations and Gene Pools

•Population – group of individuals of the samespecies occupying a given area at the sametime and sharing a common set of genes

•Gene Pool – The sum of all alleles for all traitsin a sexually reproducing population

•4 ways the gene pool changes: independentAssortment, crossing over, chancefertilization, mutations

Most, if not all, Populations areEvolving

•Hardy-Weinberg theorem states thatevolution stops only when 4 principles aremet:

•Large population size

•No migration in or out

•No mutations

•Sexual reproduction must be random

Four Mechanisms of EvolutionaryChange

•Genetic Drift - chance events influencing thefrequencies of genes

•Gene Flow - immigration or emmigration in apopulation

•Mutation - changes in the structure of genesand chromosomes

•Natural Selection - certain phenotypes havingan environmental advantage over otherphenotypes (survival of the fittest)

Types of Selection

•Disruptive Selection - produces distinctsubpopulations

•Sexual Selection - mating patterns thatproduce varying degrees of success ofindividuals of a population

•Stabilizing Selection - narrows the phenotypicrange

Speciation

•Speciation – the formation of a new species (canonly occur through reproductive isolation)

•Allopatric Speciation – occurs when populationsbecome geographically isolated

•Parapatric Speciation – occur in small, localpopulations (ex. frogs in an isolated pond)

•Sympatric Speciation – occurs within a singlepopulation (brood parasites)

Rates of Evolution

•Phyletic Gradualism – slow, continuouschange over long period of time (Darwin)

•Punctuated Equilibrium – rapid change,followed by periods of stasis, or no change,over long periods of time

Molecular Evolution

•Using molecular genetics to study base-paringin DNA is a high-tech way of trackingevolution through the genome

Mosaic Evolution