Download Genes and Variatoin

What is it?
Genes and Variation
Presented by: Mr. Godinez
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.