2 7 Forces of evolution o Account for variability we see in the frequency of alleles 1 Mutation change in DNA Change in coding for protein o Example sickle cell anemia Source of new genetic material 2 Gene Flow Exchange of genetic material between populations Example island population has high O blood type o After a small mix with another population the frequency could drop dramatically 3 Genetic Drift Small population size 2 kinds o Population bottleneck Some force of nature wipes out a good portion of the population On one island 1 in 12 people are colorblind Hurricane killed most of population King lived and was totally colorblind Breeding ensues Everyone is colorblind o Founder s Effect Small group breaks off into new population Reduced variation in population Change in allele is from low population instead of large change 4 Recombination Variation from sex cells 5 Natural Selection Change in allele as the result of differential reproductive fitness Allele confers an advantage o If an allele is in appreciable frequency 1 we look for a cause In Africa 20 of the population have sickle cell anemia Map of sickle cell frequency overlaps clearly with malaria Falciparam malaria is carried by mosquitos Plasmodium that could be malaria enters RBCs o Multiplies using RBCs as hosts o Continues acting on cells RBCs have hemoglobin HbA and HbS alleles are co dominant o If you have one of each enough of your hemoglobin is okay for sickle cell not to occur Deleterious allele HbS goes up in frequency as a result of another force malaria Balanced polymorphism o Multiple alleles o Heterozygotic advantage o Polymorphism Most of our genes are constant non polymorphic 28 have alleles Type O people o Resistance to salmonella and shigella o Preferred by mosquitos This can account for geographic differences Type A Low frequency in smallpox areas o Smallpox uses molecular mimicry to trick cells Looks like A antogen so the body doesn t pick up on its presence Lactose in tolerance Chromosome 2 Autosomal dominant o Lactose sugar in breast milk o Lactase enzyme that breaks it down from lactating o Most mammalian species turn off lactase production around weaning age
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