16.216.2Evolution as Genetic Change

The effects of Natural Selection cause changes in whole populations,

not just in individuals.Therefore the genetics of the

population will change.

Evolution of dolphins

Natural Selection on Natural Selection on Polygenic TraitsPolygenic Traits

Natural selection operates on Natural selection operates on variations of traits within a variations of traits within a population. population.

The distribution of traits in a The distribution of traits in a population changes population changes over timeover time..

There are 3 general patterns of trait There are 3 general patterns of trait changes in a population as a result changes in a population as a result of of natural selection.natural selection.

1. DIRECTIONAL SELECTION:

An extreme phenotype becomes a favorable adaptation

2. STABILIZING SELECTION:

The average phenotype is favored for survival.

The extreme phenotypes are un-favored.

3. DISRUPTIVE SELECTION

The average phenotype is not favorable, but the extreme phenotypes become favored adaptations.

Can eventually lead to 2 species.

Hardy-Weinberg Hardy-Weinberg PrinciplePrinciple

If the allele frequencies do not change, the population will not evolve.

This will be This will be true if 5 true if 5 conditions are conditions are met.met.

Flamingo Flamingo populationpopulation

Hardy-Weinberg Genetic Hardy-Weinberg Genetic EquilibriumEquilibrium

Random mating. [Seldom happens.] Very large populations. [Can

happen.] No immigration and no emigration.

[Can happen.] No mutations. [Seldom happens.] No natural selection. [Seldom

happens.]

Therefore, evolution is a given, it cannot be stopped. There are no conditions known under which evolution does not happen!

Evolution of land animals

Genetic DriftGenetic Drift

Happens in Happens in small small populations.populations.

An allele An allele becomes more or becomes more or less common less common easier.easier.

Random chance Random chance events events lead to lead to these changes these changes in gene in gene frequencies.frequencies. Bull Tule Elk at Pt. Bull Tule Elk at Pt.

ReyesReyes

Founder Founder EffectEffectFounding populations are completely separated from the original population, as well as from other founding populations when they colonize a new habitat.