Measuring Evolution of Populations AP Biology 5 Agents
Measuring Evolution of Populations AP Biology
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
Mechanisms of Evolution AP Biology
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
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
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 play video
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
Testing a hypothesis WS § Making of the Fittest AP Biology
Any Questions? ? AP Biology 2014
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