Explain why variations in a population are seen as a bell shaped curve. Agenda for Friday Feb 20 th 1.Patterns and Mechanism notes 2.Go over variation lab

Genetic Equilibrium Allele frequency in a gene pool is not changing –Hardy Weinberg Disruption of Equilibrium = Change

1. Natural Selection

Types of Natural Selection Directional Selection - extreme phenotype has higher fitness Peppered Moth

Stabilizing Selection - intermediate phenotype has a higher fitness

Disruptive Selection - intermediate phenotypes are of lower fitness than extreme phenotypes

2. Mutation Neutral mutation – no impact on survival or reproduction Beneficial mutation – increase in survival or reproduction

3. Gene Flow/Migration Individuals enter or leave a population –emigrate = lose alleles –immigrate = gain alleles

4. Genetic Drift Unpredictable changes in allele frequency due to small population size –Population bottleneck –reduction of a population –Founder Effect – individuals leave a population and establish a new one

5. Nonrandom Mating Choosing a mate Sexual Selection – ability to attract a mate

Patterns of Evolution

Coevolution Change of two or more species in close association with each other Predators and prey Parasites and hosts Plant eating animals and plants

Convergent Evolution Environment selects similar phenotypes although ancestral types were different Sharks and dolphins

Divergent Evolution Two or more related populations or species become more and more different Response in differing habitats Result in new species

Adaptive Radiation Many related species evolve from a single ancestral species

Artificial Selection Intentional breeding for specific traits

Rates of Evolutionary Change Rapid rates of evolution occur when conditions favor new traits –Otherwise evolution is slow Based on many factors –Mutation rate, lifespan of organism

Rate of Speciation

Patterns of Evolutionary Change Novel features evolved infrequently –Most changes are modifications Organisms have increased in size and complexity Predations rates increased = evolution of better defenses

Describe convergent evolution. Agenda for Thursday May 29 th 1. Bunny Lab