5 Agents of evolutionary change Mutation Gene Flow

5 Agents of evolutionary change Mutation Gene Flow Non-random mating Chemical Changes to DNA Migration Sexual Selection AP Biology Genetic Drift Selection Small population Natural Selection Differential Survival

AP Biology

AP Biology

Heterozygote Advantage Measuring Evolution of Populations AP Biology 2010 -2011

AP Biology

Example of heterozygote advantage § Sickle cell anemia u inherit a mutation in gene coding for one of the subunits in hemoglobin § § u oxygen-carrying blood protein normal allele = Hb mutant allele = Hs recessive trait = Hs. Hs low oxygen levels causes RBC to sickle § clogging small blood vessels § damage to organs u AP Biology often lethal

Sickle cell frequency § High frequency of heterozygotes 1 in 5 in Central Africans = Hb. Hs u unusual for allele with severe detrimental effects in homozygotes u § 1 in 100 = Hs. Hs § usually die before reproductive age Why is the Hs allele maintained at such high levels in African populations? Suggests some selective advantage of b Hs being heterozygous… H AP Biology

Single-celled eukaryote parasite (Plasmodium) spends part of its life cycle in red blood cells Malaria 1 liver 2 AP Biology 3

Heterozygote Advantage § In tropical Africa, where malaria is common: u homozygous dominant (normal) § reduced survival or reproduction from malaria: Hb. Hb u homozygous recessive § reduced survival & reproduction from sickle cell anemia: Hs. Hs u heterozygote carriers § survival & reproductive advantage: Hb. Hs Hypothesis: In malaria-infected cells, the O 2 level is lowered enough to cause sickling which kills the cell & destroys the parasite. AP Biology Frequency of sickle cell allele & distribution of malaria

Hardy-Weinberg equilibrium § Hypothetical situation u u serves as null hypothesis non-evolving population REMOVE all agents of evolutionary change 1. no genetic drift (very large population size ) 2. no gene flow (no migration in or out) 3. no mutation (no chemical change to DNA) 4. random mating (no sexual selection) 5. no natural selection (equal survival) AP Biology

Any Questions? ? AP Biology 2010 -2011

Example of strong selection pressure § Tay Sachs primarily in Ashkenazi Jews & Cajuns u recessive disease = aa u lysosomal storage disease u § lack of one functional digestive enzyme in lysosome § build up undigested fat in brain cells § children die before they are 5 years old So where do new cases of come from? APTay-Sachs Biology