Meiosis- Replication- genes cross over, or recombine into new combinations First division, each cell has 23 pairs of chromosomes Second division- each cell has just one cope of each of the 23 chromosomes Genotype not always predictable from phenotype. With XX or XY, phenotype usually ~ genotype eg. ABO blood groups -determined by 3 alleles (A, B, O) -everyone has 2 alleles 4 phenotypes 6 genotypes Type A AA AO Type B BB BO Type O OO Type AB AB A and B alleles are dominant, mask recessive O allele in heterozygous genotypes. Type O phenotype is only if homozygous genotype. Codominant alleles express distinctive phenotypes. Most people and animals select mates based on phenotypes Degree to which phenotypes reflect genotypes affects offspring genotypes -different- negative assortative mating ?opposites attract?- from a genetic POV, it?s a good thing- genotypic difference -similar- positive assortative mating- phenotypically similar, not good in an evolutionary case, offspring less diverse -inbreeding is an extreme case Inbreeding- when close biological relatives reproduce -lower genetic variation of offspring -increases risks of deleterious homozygous recessives Incest taboos- cultural practice: -social consequences -biological consequences -evolutionary consequences Inbreeding avoidance in animals- product of natural selection? -endangered species: small, isolated populations -can?t always avoid inbreeding -close inbreeding can lead to extinction -loss of genetic diversity -increased risks of deleterious homozygous recessive traits Genetic drift- random loss of alleles, affected by population size, possible that you end up with a genetically different population than from which you started -works faster in smaller populations -founder effects- small representation of entire gene spectrum -endangered species Gene flow- moves through organisms that carry them- from population A to population B, brings particular genetic characteristics with them which are passed on when they reproduce in the new population Increases variation within population, but also reduces variation between populations Natural selection- acts on variation present in populations Body Size graph- bell curve- directional selection- trait vs. frequency -has an average height directional selection- moves average in graph in one direction- shifts graph stabilizing selection- takes graph and stabilizes it- makes it a bell curve, optimizes it, good if the environment is stable disruptive selection- takes bell curve and stretches it to the extreme in both directions- pulls in opposite directions, can lead to creation of new species Review of evolutionary processes: Genetic Variation Mutations- increase genetic variation Sexual reproduction- increase genetic variation inbreeding- deceases genetic variation Genetic drift- decreases genetic variation Gene flow- increases genetic variation within population -decreases genetic variation between populations Natural selection- effect on genetic variation depends completely on environment
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