Genetic Variation There are two main sources of genetic variation: Mutation Gene shuffling that results from sexual reproduction Some variation is “invisible”

Turn to your table-mates: What are some of the genetic variations in these babies?

- Ability to resist certain diseases Visible? Invisible? - Ability to resist certain diseases - Hair texture - Skin color - Size - Blood type

Genetic variation is studied in populations. Recall: What is a population? A gene pool consists of all genes, including all the different alleles, that are present to a population.

Relative Frequency of Alleles The relative frequency of an allele is the number of times that allele occurs in a gene pool (compared with the number of times other alleles for the same gene occur).

What is the relative frequency of the brown allele. The black allele What is the relative frequency of the brown allele? The black allele? (50 total/20 black/30 brown)

Relative frequency of…. - Dominant (black) = 40% Relative frequency of… - Dominant (black) = 40% - Recessive (brown) = 60% Note: The relative frequency of an allele has nothing to do with whether it is dominant or recessive.

If the relative frequency of the black allele decreased, what would happen to the relative frequency of the other allele?

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

Sources of Genetic Variation Mutations Gene Shuffling that results from sexual reproduction.

Mutations A mutation is any change in a sequence of DNA Mutations occur because of mistakes in DNA replication radiation or chemicals in the environment Some mutations do not affect an organism’s phenotype, some do Fitness

Gene Shuffling Most heritable differences are due to gene shuffling occurs during the production of gametes during meiosis.

Crossing-over further increases the number of different genotypes that can appear in offspring.

Sexual reproduction produces different phenotypes, but it does not change the relative frequency of alleles in a population. i.e. no matter how many times you shuffle a deck of cards, the probability of drawing a particular card will remain the same.

Q: What determines how many phenotypes there are for a given trait?

Single Gene Traits Single-gene traits are controlled by a single gene that has two alleles. Variation only leads to two possible phenotypes.

Polygenic Traits Polygenic traits are controlled by two or more genes. Polygenic traits have many possible genotypes and phenotypes.

They exhibit a continuum of expression in a bell shaped or “normal distribution” curve.

A: The number of phenotypes produced for a given trait depends on how many genes control the trait.

Exit slip questions: How do you think the relative frequency of alleles varies between the salamander subspecies in CA? Give an example of a polygenic trait for salamanders.