Evolution of Populations

Genetic Variation mutations genetic shuffling Natural selection  allele frequencies changes  evolution

Example Red lizards Black lizards more visible to predators less likely to survive and reproduce allele for red coloring become rare Black lizards absorb more sunlight  warm up faster move faster to feed and avoid predators produce more offspring Alleles for black become common

Natural Selection on Polygenic Traits Direction Selection: individuals at one end of the curve have higher fitness beak size & thickness

Beak Size in Birds

Natural Selection on Polygenic Traits Stabilizing Selection - individuals near the curve’s center have higher fitness Size of baby at birth

Natural Selection on Polygenic Traits Disruptive Selection - individuals at the upper and lower ends of the curve have higher fitness Environment with few medium size seeds

Genetic Drift Small population individuals with a particular allele may leave more descendants by chance With more chance occurrences an allele to become common in a population. Founder Effect: allele frequencies change due to a subgroup’s migration

Genetic Drift

Hardy – Weinberg Principle allele frequencies remain constant unless factor(s) change frequencies Requirements of Hardy-Weinberg random mating very large population no movement in or out of the population no mutations no natural selection

Speciation: new species formation Reproductive Isolation: 2 populations cannot interbreed and produce fertile offspring Behavioral Isolation Different courtship rituals Different reproductive strategies Geographic Isolation geographic barriers; rivers, mountains Temporal Isolation reproduce at different times of the year