16-1: Genes and VariationGregory Shook

Darwin’s HandicapsMendel’s work was published but ignoredDidn’t know how traits are inheritedDidn’t know how variation appeared

Modern Evolutionary Theory1930’s, molecular biology/genetics combined

with Darwin’s theoriesDNA structure allowed the molecular nature

of mutations to be illustrated

How Common is Genetic Variation?Many genes have 2 allelesSome genes ‘invisible’ because it involves

biochemical processesFish, reptiles, and mammals are typically 4-

8% of their genes heterozygous

Variation and Gene PoolsA 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 VariationMutations: 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 TraitsThe number of phenotypes possible depends

on how many genes control that traitA single-gene trait is controlled by one gene,

and has two alleles Widow’s peak in humans is an example

Polygenic TraitsTraits controlled by many genes are called

polygenic traitsEach gene often has different allelesHuman height is an example