Today’s Objectives: 10/21/02 TSW be able to write the Hardy-Weinberg equation and explain it. TSW be able to list several evolutionary mechanisms. TSW be able to list several types of speciation and discuss the rates of evolution.
Hardy-Weinberg Theorem p2 + 2pq + q2 = 1 Studies genetic (allelic frequencies)
H-W Assumptions: Large population size. Random mating. No migration. No mutations or mutational equilibrium.
Ways Evolution Can Occur
Genetic Drift Neutral selection – caused allelic frequencies to change based on chance Founder effect Bottleneck effect (mutation can play a part here) Founder effect – Dunker populations of Pennsylvania who do not intermarry because of religious reasons, some blood types unknown Bottleneck effect – cheetahs, other endangered species.
Gene Flow Changes allelic frequencies because of migration of individuals.
Mutation Random events. May be beneficial, harmful or insignificant.
Definition Selection Pressure Natural Selection Definition Selection Pressure Whenever some phenotypes are more successful than others. Selection pressure occurs that helps the more successful phenotype to increase its frequency in a population.
Types of Natural Selection Directional selection Industrial melanism in Biston betularia Disruptive selection Distinct subpopulations Stabilizing selection Keeps phenotypes stable for long periods of time.
Reproductive isolation must be achieved! Speciation Reproductive isolation must be achieved! Premating isolation – impenetrable barriers separating populations Postmating isolation – cannot produce viable offspring (hybrids often sterile – ex. Ligers and mules)
Types of Speciation Allopatric Parapatric Sympatric Geographic isolation – most common type Adaptive radiation Parapatric In small, local subpopulations (demes) Sympatric Almost always in plants In same population but do not interbreed
Gradualism vs. Punctuated Equilibrium Rates of Evolution Gradualism vs. Punctuated Equilibrium
Same structure is modified for multiple uses. Mosaic Evolution Same structure is modified for multiple uses.