genetic drift notes

genetic drift notes - NO EVOLUTION: HARDY WEINBERG...

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NO EVOLUTION: HARDY WEINBERG EQUILIBRIUM EVOLUTION -CHANCE (GENETIC DRIFT) -NATURAL SELECTION HARDY - WEINBERG EQUILIBRIUM (GENETIC EQUILIBRIUM) -NO CHANGE IN *allele frequencies between generations *genotype frequencies between generations DERIVED INDEPENDENTLY IN 1908 BY Godfrey H. Harding Wilhelm Weinberg CONCLUSIONS: UNDER HARDY-WEINBERG EQUILIBRIUM (1) THE ALLELE FREQUENCIES IN A POPULATION WILL NOT CHANGE, GENERATION AFTER GENERATION (2) IF THE ALLELE FREQUENCIES IN A POPULATION ARE GIVEN BY p AND q, THE GENOTYPE FREQUENCIES WILL BE GIVEN BY: P 2 , 2pq, q 2 ASSUMPTIONS (1) NO DIFFERENTIAL REPRODUCTIVE SUCCESS (2) INFINITELY LARGE POPULATION (3) NO MUTATION (4) NO MIGRATION (5) RANDOM MATING GENETIC DRIFT * Chance changes in allele frequency within a population between generations Outcomes: (1) Random changes in allele frequencies between generations (2) Random loss of alleles * decreases diversity within the population GENETIC DRIFT * Occurs in all populations, regardless of size * Greatest effect in small populations Two named special cases related to cause: (1) Population Bottleneck (2) Founder effect
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In both cases very small populations are produced that can experience dramatic changes in allele frequencies. POPULATION BOTTLENECK: = Very large population dramatically reduced in size Example: Northern Elephant seals ( Mirounga angustirostris ) -hundreds of thousands originally present - 1892: 50-100 remained - slaughtered for blubber -1922, protected by Mexican govt. -US followed a few years later -now, about 160,000 *24 electrophoretic loci: no genetic variation -Allelic variation much higher in southern elephant seal ( Mirouga leonina) FOUNDER EFFECT: * Small population disperses from large ancestral population *"Founds" new population of a species POSSIBLE EXAMPLE: ABO BLOOD GROUPS Genotypes I A I A I A I B I B I B I O I O I A I O ----- I B I O ------ Phenotypes A AB B 0 Universal Universal Receiver donor NATIVE AMERICANS ARE MISSING THE B ALLELE -ALTHOUGH ASIANS (ANCESTRAL) POSSESS ALL FOUNDER EFFECT: Ellis-van Crevald Syndrome Amish of E. Pennsylvania *200 settlers in 18 th century *Mr. or Mrs King (or both) -carriers for recessive on 4 th chromosome =Ellis-van Crevald Syndrome -rare dwarfism In most human populations frequency = 0.001 In Amish population frequency = 0.07 Note that founder effect was immediate: From 0.001 in background population (probable) To 0.0025 if there was 1 allele in 200 individuals EXAMPLE FROM NATURE: Silvereye, Zosterops lateralis
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This note was uploaded on 04/24/2008 for the course BIOL 102 taught by Professor Baker/robertson during the Fall '08 term at Clark University.

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genetic drift notes - NO EVOLUTION: HARDY WEINBERG...

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