Mechanisms for Evolution 1

Population Genetics: Measuring the changes in alleles within a population over generations. Causes of Variation: A. Mutations B. Crossing -over during meiosis C. Independent Assortment D. Random fusion of gametes

Populations evolve, not individuals Individuals cannot evolve a new phenotype in response to the environment.

Gene pool -the genetic composition of a population; (all of the alleles of a population’s genes for a particular trait) Allele frequency - the relative frequency of a particular allele in a population (% or fraction) for a particular trait.

Read example in notes and Refer to fig. 16-2 on page 394.

a useful variation, produce new alleles for traits. Factors that disrupt genetic equilibrium: 1. Mutations that become a useful variation, produce new alleles for traits.

2. Gene Flow (migration) - the transport of genes when individuals enter (Immigration) and leave (Emigration) populations 7

3. Genetic Drift – Allele frequency changes as a result of chance events like storms, floods, fires, or other acts of nature Changes have a greater effect on small populations with small gene pools ex. What if a fire killed off most of the black mice in the population?

4. Nonrandom mating (Sexual Selection) Nonrandom Mating: Mating based on preferences Most species do not mate randomly, but rather choose a mate based on desirable traits Example: a female may choose a mate based on male size, color, or ability to gather food.

5. Natural selection acts on variations that increase or decrease an organism’s chance for survival 3 different types of natural selection on variation

Stabilizing selection natural selection favors average individuals in a population Average sized salmon are “selected for”

Directional selection natural selection favors small or large extreme variation of a trait woodpeckers with long beaks are “selected” over those with short or normal beaks

Disruptive selection individuals with either extreme of a trait’s variation are selected for dark and light limpets over normal (tan) limpets (sea snail) 13

Peppered Moth There are two variations in color of peppered moths, light and dark.

Prior to the industrial revolution, tree trunks were light colored. Predators were more likely to pick the dark moths. As a result, the moth population was primarily light.

http://www. globalchange. umich http://www.globalchange.umich.edu/gctext/Inquiries/Inquiri es_by_Unit/Unit_3a_files/image004.jpg

After the industrial revolution, trees were covered in soot making them dark. Now, predators were more likely to pick the light moths. As a result, the population shifted from being primarily light to primarily dark.

http://www. globalchange. umich http://www.globalchange.umich.edu/gctext/Inquiries/Inquiri es_by_Unit/Unit_3a_files/image004.jpg

What type of selection is this an example of ?

Sexual Selection: