HIST 202 Lecture : History 202 Notes
15 Mar 2019
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Due to heterozygotes having higher fitness than homozygotes: balanced polymorphism: ex) sickle cell trait: Heterozygotes for sickle cell have selective destruction of red blood cells (rbcs). Uninfected rbcs do not sickle; infected rbcs sickle and kill parasites. Selection acts of the phenotypic/genotypic variability that exists in a pop. Pops. differ in their rbc mutations: sickle cell, thalassemia, and g-6-pd. Each rbc variant is selectively advantageous in malarial environment; consequently, each variant is perpetuated by natural selection. Interaction of natural selection and mutation means that pops. may show different adaptations to the same environmental stress: human bio, lactose tolerance and intolerance. Lactase enzyme that allows you to digest lactose, which is a sugar in milk. With long histories of dairying are typically lactose tolerant: mutation for ability to digest milk as adults would have provided a natural selective advantage, human variation: Definition: polytypism phenotypically different pops. in a species. Polytypism is result of diversity of environments that we inhabit.
