AP Bio Study Guide

Big Idea 1.A

What factors preserve genetic variation?

  • Sexual reproduction. This includes independent assortment of chromosomes (where different genes separate from each other randomly during the formation of gametes during metaphase I), crossing over (where genetic material of homologous chromosomes is exchanged during meiosis 1), and random fertilization (where the sperm and egg that fertilize are randomly chosen).
  • Outbreeding (the opposite of inbreeding). This is where organisms that are not closely related mate (e.g. males leave their pride to mate with females from another pride), which strengthens the gene pool by combining varied traits.
  • Heterozygote advantage. Sometimes, there is an advantage to having the heterozygote genotype (e.g. in sickle cell anemia in West Africa, heterozygotes do not have the disease and are resistant to malaria). This preserves multiple alleles in the population.