Gregory Shook

Darwin’s Handicaps Mendel’s work was published but ignored Didn’t know how traits are inherited Didn’t know how variation appeared

Modern Evolutionary Theory 1930’s, molecular biology/genetics combined with Darwin’s theories DNA structure allowed the molecular nature of mutations to be illustrated

How Common is Genetic Variation? Many genes have 2 alleles Some genes ‘invisible’ because it involves biochemical processes Fish, reptiles, and mammals are typically 4-8% of their genes heterozygous

Variation and Gene Pools A gene pool is all the genes, including different alleles, that are present in a population Relative frequency of an allele is the number of times that allele is in the gene pool In genetic terms, evolution is any change in the relative frequency of alleles in a population

Sources of Genetic Variation Mutations: A mistake in the genetic sequence Some may be neutral, some may change a phenotype Change may have an effect on fitness, may not Gene shuffling ***Sexual Reproduction*** Individuals don’t look identically like either parent In meiosis, each part of a homologous pair of chromosomes migrate independently Humans have 8.4 MILLION different gene combinations Crossing over further increases changes to the genotype

Single-Gene and Polygenic Traits The number of phenotypes possible depends on how many genes control that trait A single-gene trait is controlled by one gene, and has two alleles Widow’s peak in humans is an example

Polygenic Traits Traits controlled by many genes are called polygenic traits Each gene often has different alleles Human height is an example