What is a phylogenetic tree? Agenda for Tuesday Nov 30 th 1.Mechanisms of Evolution notes

Genetic Equilibrium A genetic equilibrium occurs when an allele within a gene pool is not changing in frequency (i.e. evolving)

Disruption of Genetic Equilibrium Natural Selection Mutation Migration Genetic Drift Nonrandom Mating

Natural Selection

Types of Natural Selection Directional Selection - extreme phenotype has higher fitness than other phenotypes

Stabilizing Selection Stabilizing Selection - intermediate phenotypes have a higher fitness that extreme phenotypes

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

Mutation Mutations can change one allele into a different allele Neutral mutation – affects phenotype, no impact on the survival or reproduction Beneficial mutation – affects phenotype, increase in survival or reproduction

Gene Flow/Migration Individuals leave a pop. or new individuals enter a pop. –emigrate = lose alleles –immigrate = gain alleles

Genetic Drift Unpredictable changes in allele frequency due to small population size Population bottleneck –reduction of a population –Natural disaster Founder Effect – few individuals separate from a large population and establish a new one

Nonrandom Mating Limited probability of mating with any other individual in the population Assortative mating – individuals select partners that are like themselves –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 quite different Sharks and dolphins

Divergent Evolution Two or more related populations or species become more and more dissimilar 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 –Speeds up divergent evolution

Rate of Speciation Gradualism Punctuated