Genes and Variation 17.1

Genotypes and phenotypes in evolution Natural selection acts on phenotypes and does not directly on genes. Natural selection favors members of a population that are the most fit.

How is evolution defined in genetic terms? Gene pool contains all the alleles of all the genes in a population. Allele frequency is the number of times an allele occurs in a gene pool, compared to the total number of alleles for the same gene in the pool. Evolution is defined by the change in the frequency of alleles in a population over time.

Sources of genetic variation Mutations = genetic change Sexual reproduction – crossing over in meiosis Lateral gene transfer - bacteria

What determines the number of phenotypes for a given trait? The number of phenotypes depends on how many genes or alleles control the trait: – Single gene trait –complete or incomplete dominance. – Multiple allele – blood types – Polygenic – skin color

Human height example polygenic trait Hair line example single gene trait