Chapter 17: Evolution of Populations Section 17-1: Genes and Variation

Genetics Joins Evolutionary Theory Heritable traits controlled by genes Changes in genes/chromosomes result in variation Genotype = particular allele combination, along with environmental condition determines phenotype Natural selection acts on phenotype – some variations provide advantages, increasing fitness

Populations and Gene Pools A gene pool consists of all the genes, including all the different alleles, for each gene present in a population Study relative frequencies of alleles Evolution is any change in the relative frequency of alleles in the gene pool of a population over time Natural selection acts on individuals, but populations evolve

Sources of Genetic Variation There are 3: Mutations Genetic recombination Lateral gene transfer

Mutations Mutations resulting in changes to phenotype may increase fitness, decrease fitness, or have no affect Only matter in evolution if they are passed on – must occur in egg or sperm

Genetic Recombination Occurs during sexual reproduction Independent assortment produces millions of combinations Crossing over

Lateral Gene Transfer Organisms pass genes from one individual to another – not offspring Can occur between organisms of same or different species Variation increases in species that picks up “new” genes

Single-Gene Traits A trait controlled by only one gene Can have 2 or 3 distinct phenotypes Most common form of the allele can be dominant or recessive Just because an allele is dominant does not mean it necessarily appears in greater frequency

Polygenic Traits Traits controlled by 2 or more genes Each gene often has 2 or more alleles Many possible genotypes/phenotypes