Microevolution

Levels of Evolutionary Study Microevolution: examines changes to the genes (alleles) within populations –Population Genetics: studies the changes in the numbers & types of alleles in a population Examines evolution within a species. Small changes that do not lead to new species, but can lead to new variations. Macroevolution: examines the evolutionary changes that create new species –Speciation: the formation of new species over time

Processes of Microevolution Microevolution examines the processes by which inherited traits change over time in a population –Natural Selection –Migration –Mate Choice –Mutation –Genetic Drift

Processes of Microevolution Natural Selection: changes in environmental pressures can cause an increase or decrease in certain alleles (traits) in a population –Favorable alleles stay in population (selected for) –Unfavorable alleles are eliminated (selected against) Migration: as organisms move from one population to another, their genes move with them –Causes the numbers and types of alleles within each population to change.

Processes of Microevolution Mate Choice: if parents are selective (picky) or limited in their choice of mates, only a limited set of traits will be passed on Mutation: can add a new allele to a population –Mutations are rare, and must occur in egg or sperm to be passed on Genetic Drift: population sizes affect the change in alleles (traits) in a population –Large populations experience slower changes in alleles –Smaller populations can change more quickly

Microevolution: Changes within Populations Populations evolve NOT individuals evolve Natural selection works on the phenotypes within a population Individuals cannot evolve within their lifetime, because they cannot evolve a new phenotype due to a change in the environment Evolution is brought about by breeding that occurs between organisms within a population. Natural selection maintains favorable (useful) genotypes, and eliminates unfavorable (not useful) genotypes.

- Explains how organisms change over time Natural Selection 1.Over Production: 1.Over Production: Most organisms produce more offspring than will survive 2.Variation: 2.Variation: Members of the population have variations 3.Selection: 3.Selection: Certain variations will increase the likelihood of survival 4.Adaptation: 4.Adaptation: Over-time organisms with that variation make up most of the population and may look different than their ancestors

Patterns of Natural Selection Stabilizing selection: Favors average individuals; reduces variation Directional selection: Favors EXTREME variations; evolution is fast Disruptive selection: Favors two extreme variations; no intermediate and eventually two species.

Stabilizing Selection “Average” individuals are better able to survive Alleles for the “extreme” are eliminated A narrow range of phenotypes is favored resulting in a narrow bell shaped curve

Directional Selection ONE extreme is favorable, but other is not Alleles for other extreme and normal phenotypes become less common in the population Results in FAST evolution! Bell curve is shifted off of center

Disruptive Selection BOTH extremes are favorable! Results in increasingly distinct phenotypes, the “normal” phenotype is selected against Bell curve is ‘disrupted’ and pushed apart into two peaks