LIFESCI 1 Lecture Notes - Lecture 4: Heterozygote Advantage, Balancing Selection, Sickle-Cell Disease
Document Summary
Selection: fixation = allele has frequency of 1. Natural selection increases frequency of beneficial alleles. New advantageous allele can exist as only 1 copy in a single individual. Eventually, it will replace all other alleles in a population = positive selection: majority of mutations to functional genes = deleterious. Lethal to individuals and eliminated right away. Natural selection can be inefficient at getting rid of bad alleles (negative selection) Genetic disease occurs rarely and allele remains in population because it is not expressed as a heterozygote: balancing selection = natural selection can maintain frequency of allele between. Acts on 2+ alleles in a population. Same species living in different environments have different alleles favored based on location. As a whole, however, the species still has intermediate allele frequencies. Also occurs if heterozygote"s fitness is higher than either homozygotes. African population of sa gene is protected against malaria and sickle cell disease; but in areas w/ no threat of malaria, the.
