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Transcript
Population genetics is a field of biology that studies the genetic composition of biological populations, and the changes in genetic composition that result from the operation of various factors, including natural selection. AP Bio Lab #8 Population Genetics Part I PTC Paper ¯ PTC paper at front desk... Tasters (p2 + 2pq) Nontasters (q2) Part I PTC Paper *North American white population 0.45 0.55 *Japanese population 0.73 0.27 *Jewish population 0.47 0.53 *Hindu population 0.42 0.58 *Brazilian population 0.89 0.11 **Overall North American 0.55 0.45 Population genetics is a field of biology that studies the genetic composition of biological populations, and the changes in genetic composition that result from the operation of various factors, including natural selection. Ideal Parameters Everyone begins as a heterozygote Grab your gametes children!! Time to breed… RANDOMLY! Shuffle your gametes children!! Time to breed… RANDOMLY! Turn over the top “gamete” on your pile Lets just say… Your gameteYour partner’s gamete your F1 Time to breed… RANDOMLY! SHUFFLE AGAIN Time to breed… RANDOMLY! Your gameteYour partner’s gamete Your partner’s F1 Everyone takes the genotype of their F1… Grab your NEW 4 gametes!! Time to mate… RANDOMLY (go to Shuffle your someone else)!new F1 gametes Time to breed… RANDOMLY! Turn over the top “gamete” on your pile Time to breed… RANDOMLY! Your gameteYour partner’s gamete your F2 And again… for the F3 generation And again… for the F4 generation And again… for the F5 generation NO MATING OUT OF TURN PLEASE!!!! Selection Selection against homo-recessive Inflicted die before reproductive age If aa is drawn your offspring will not survive, draw again w/ same parents Get gametes for your F1 generation Aa Inflicted die before reproductive age If aa, you die, shuffle and draw again heterozygote advantage heterozygote advantage Aa = immune Application of H-W principle • Sickle cell anemia – inherit a mutation in gene coding for hemoglobin • oxygen-carrying blood protein • recessive allele = HsHs –normal allele = Hb – low oxygen levels causes RBC to sickle • breakdown of RBC • clogging small blood vessels • damage to organs – often lethal Sickle cell frequency High frequency of heterozygotes 1 in 5 in Central Africans = HbHs unusual for allele with severe detrimental effects in homozygotes 1 in 100 = HsHs usually die before reproductive age Why is the Hs allele maintained at such high levels in African populations? Suggests some selective advantage of being heterozygous… Malaria Single-celled eukaryote parasite (Plasmodium) spends part of its life cycle in red blood cells Heterozygote Advantage • In tropical Africa, where malaria is common: – homozygous dominant (normal) • die or reduced reproduction from malaria: HbHb – homozygous recessive • die or reduced reproduction from sickle cell anemia: HsHs – heterozygote carriers are relatively free of both: HbHs • survive & reproduce more, more common in population Hypothesis: In malaria-infected cells, the O2 level is lowered enough to cause sickling which kills the cell & destroys the parasite. Frequency of sickle cell allele & distribution of malaria If Aa is drawn that is good… If AA is drawn This could be bad… flip a coin to determine if it survives If AA is drawn Heads = death Tails = survive Genetic Drift Genetic Drift Allele is lost… solely by chance instead of via. “selection”