APBI 200 Lecture Notes - Chronic Condition, Valine, Birth Weight
Document Summary
How is variation maintained in a population? (4) Variation is usually good because if there is an environmental change, there needs to be natural selection (which requires genetic variation) so that the species does not die out. Refers to the number and relative frequency of alleles that are present in a particular population: sexual reproduction, diploidy, balanced polymorphism heterozygote advantage, frequency-dependent selection, sexual reproduction. In meiosis, independent assortment as well as crossing over occur, which contributes to variation in individuals: diploidy 2 alleles for every gene. Recessive alleles hide and are not expressed when there is a dominant allele. Both parents contribute an allele, and both must give a recessive allele for there to be a recessive phenotype. This means that having a recessive phenotype is less likely to occur which is a good thing if the recessive allele is bad": balanced polymorphism heterozygote advantage.
