Chapter 17 Evolution of Populations 17.2: Evolution as Genetic Change in Populations

A. How Natural Selection Works Evolutionary Fitness: passing genes on to next gen Evolutionary Adaptation: genetic trait indiv’s ability to pass on alleles Natural Selection on Single-Gene Traits: Changes in allele freq=changes phenotype Causes Genetic Change Natural Selection On Polygenic Traits More complex Can affect fitness of phenotypes to prod 1 of 3 types of selection Directional Stabilizing Disruptive

Directional Selection Indiv at 1 end has fitness than at middle or end Range of phenotypes shift b/c more successful at surviving & reprod

Stabilizing Selection Indiv near center of curve have fitness than at ends Keeps center of curve at current position Narrows curve overall

Disruptive Selection Indiv at outer ends of curve fitness than middle Acts against indiv of intermediate type Can use split of curve into 2

B. Genetic Drift A change in gene pool (allele freq) due to chance Genetic Bottlenecks: Reduction due to natural disasters & hunting Reduce the size of pop

The Founder Effect Few indiv colonize an isolated island, lake, or new habitat Genetic makeup ( gene pool) diff from original colony Change reduces genetic variation

C. Evolution vs. Genetic Equilibrium                                                                                                       Genetic Equilibrium: allele freq in pop remain same Hardy-Weinberg Principle: allele freq in pop remain constant unless 1 or more factors cause freq to change 5 conditions that cause evolution to occur: Nonrandom Mating Small Pop size Immigration or Emigration Mutations Natural Selection Hardy-Weinberg Formula

17.3 The Process of Speciation

A. Isolating Mechanisms Species: pop or grp of pop that can interbreed & produce fertile offspring Speciation: formation of new species Interbreeding genetically links members Reproductive Isolation: 2 pop no longer interbreed, split gene pool; evolve into 2 sep species Behavioral Isolation Geographic Isolation Temporal Isolation

1. Behavioral Isolation 2 pop develop differences in courtship rituals or other behaviors that prevent them from breeding.

2. Geographic Isolation 2 pop separated by geographic barriers ex: rivers, mountains, water

3. Temporal Isolation 2 or more species reproduce at diff times  can not interbreed Ex: flowers bloom at diff times, can’t pollinate one another