Microevolution: change in allele frequencies in a population over time. Mendel"s experiments: used pea plants to study hybridization and inheritance of traits, particulate inheritance, law of segregation, dominant/recessive alleles, genotypes, phenotypes. * hemoglobin gene: most common allele: a, genotype: aa. S allele frequent in some populations equatorial africa, india, arabia. * aa= immune to anemia, die of malaria. * as= increased immunity to malaria, mild anemia. Balanced polymorphism is a heterozygote advantage: mutation. Random w respect to need: random genetic drift. Yamano village fissioning: increases genetic drift in forming small villages, increases differences between groups, even more differences than expected: gene flow. Migration into or out of a population may be responsible for a marked change in allele frequencies. Adaptation-human body responds to environmental stress and strain in both biological and cultural way. Genotype, allele frequencies, environmental stress and strain, plasticity, development, learned culture. Stress: the selective pressure applied to a populations genotype.