The Genetic Basis of Evolution Darwin knew heredity was vital to evolution. His ideas: Random changes appear in a population Individuals vary in their traits Adaptive value of changes depends on environmental context.

Mutation Ultimate source of variation Rate of mutation in eukaryotes is 1 in 10000 DNA base pairs, on average. Many mutations are neutral, but others are not; these are the ones subject to natural selection. Low rate of mutation = slower ability of a species to adapt High rate of mutation = more variability in the species, and faster ability to adapt.

Occurs when populations are isolated. Genetic Drift Occurs when populations are isolated. Mutation continues to occur within each population, as well as inbreeding. Over time, each population accumulates different traits; they ‘drift’ away from the phenotype they once shared and become unique.

Isolating Mechanisms Geographic Behavioural Ecological Reproductive Two populations, isolated long enough from one another, and subject to Genetic Drift, will become separate species. This is Speciation.

Defining a Species: A Species is any group of potentially or actually interbreeding individuals, capable of producing viable, fertile offspring. The Eastern Meadowlark & Western Meadowlark look similar, & their geographic ranges even overlap. However, they are reproductively isolated from one another: their songs are different, & prevent mating.

Directional: One extreme is more adaptive & selected for. Selection Mechanisms Stabilizing: keeps things the same; the intermediate phenotype is most adaptive & selected for. Disruptive: Leads to change & speciation; intermediate is selected against, extremes are favoured. Directional: One extreme is more adaptive & selected for.

Selection Mechanisms

Founder Effect One part of a population breaks off from the main population & establishes a new group elsewhere. For example: Some female deer follow a young male to a new territory. Songbirds forced into new habitats Human Colonists

Founder Effect Can lead to unique genetic hallmarks: Polydactyly among the Amish Tay Sachs disease among Central European Jews Wild Horses in North America

Genetic Bottlenecks Like founder effect, but after some extreme environmental change Drastic reduction in population Limited genome left behind. Examples: Overhunting of Eur. & N.Am. Bison Survivors of natural disasters Toba catastrophe, 70 kya, for humans?

Genetic Bottlenecks

Genetic Bottlenecks