Genes and VariationPresented by: Mr. Godinez

What is it?

What is it?

•Allele: is an alternative form of a gene. • These genes are located at the same position on a

chromosome

Variation and Gene Pools

•Gene pool: consists of all genes, including all the different alleles, that are present in a population•Allele for white fur •Allele for black fur

Variation and Gene Pools

•Relative frequency: is the number of times that the allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur• Ex. Dominant B allele = 40% Recessive b allele = 60%

• In genetic terms, evolution is any change in the relative frequency of alleles in a population.

Sources of Genetic Variation

• The two main sources of genetic variation are mutations and the genetic shuffling that results from sexual reproduction

•Mutations: any change in a sequence of DNA.• Occur because of mistatkes in the replication of DNA or

radiation and chemicals in the environment

Sources of Genetic Variation

•Gene Shuffling: occurs during the production of gametes.• Independent Assortment: Chromosomes of a homologous

pair moves independently during meiosis• Crossing over, also during meiosis.

• Does not alter the relative frequencies of each type of allele in a population

Single-Gene and Polygenic Traits

• The number of phenotype produced for a given trait depends on how many genes control the trait• Single-gene trait: controlled by a single gene that has

two alleles• Ex. Widows Peak

•Polygenic traits: controlled by two or more genes that has two or more alleles• Ex. Human Height

Evolution as Genetic Change

•Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution• Ex. Population of moths (light colored with dark spots)• But experiences mutations that produce (darker) forms

•What happens to those new alleles?• If light moths are more visible to predators-less likely survive• Light colored moths may not become common

Evolution as Genetic Change•Natural Selection on poly-genic traits can affect the

distributions of phenotypes in any of three ways: • directional selection • stabilizing selection • disruptive selection

Evolution as Genetic Change•Directional Selection: when individuals at one end of

the curve have higher fitness than individuals in the middle or the other end

Evolutions as Genetic Change• Stabilizing Selection: when individuals near the center

of the curve have higher fitness than individuals at either end of the curve.

Evolution as Genetic Change

•Disruptive Selection: when individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle

Genetic Drift

Genetic Drift: a random, non-adaptive change in the gene frequencies of a population.• may result in the loss of alleles from the original

gene pool.

Genetic Drift

Bottleneck Effect: describes a situation where a large population is drastically reduced in size due to some natural disaster.

Genetic Drift

Founder Effect: describes the colonization of a new habitat by only a few individuals.

Genetic Drift

•Both have likelihood that the new population contains different proportions of alleles than the initial population.•may result in the loss of alleles from the original

gene pool.