Final answer:
Sickle-cell disease and lactose tolerance are examples of polymorphisms and natural selection in human populations. Sickle-cell disease is caused by a mutation in the gene that codes for hemoglobin, resulting in the production of sickle-shaped red blood cells. Lactase persistence is the ability to digest lactose into adulthood, and it is believed to have arisen in populations that domesticated cattle.
Step-by-step explanation:
Sickle-cell disease and lactose tolerance are examples of polymorphisms and natural selection in human populations.
Sickle-cell disease is a genetic disorder that affects red blood cells. It is caused by a mutation in the gene that codes for hemoglobin, a protein that carries oxygen in the blood. The mutated gene results in the production of sickle-shaped red blood cells, which can cause blockages in blood vessels and lead to various health problems. However, individuals who carry a single copy of the sickle-cell gene are more resistant to malaria, a disease caused by a parasite that infects red blood cells. This selective advantage has resulted in the persistence of the sickle-cell gene in populations where malaria is prevalent, such as in sub-Saharan Africa. Lactase persistence, on the other hand, is the ability to digest lactose, the sugar found in milk, into adulthood. The production of lactase, the enzyme that breaks down lactose, is usually turned off after childhood in most mammals, including humans. However, some human populations have evolved the ability to continue producing lactase throughout their lives. This adaptation is believed to have arisen in populations that domesticated cattle and started consuming milk as a food source. The ability to digest lactose provided a nutritional advantage to these populations, allowing them to utilize milk as a source of energy and nutrients.