Sickle cell anaemia: The selective forces that a population experiences can vary

Question

Sickle cell anaemia: The selective forces that a population experiences can vary by context, especially by geographic place. a) Explain in your own words how natural selection affects the evolution of haemoglobin in humans and how and why the selective pressures differ among human populations. b) For your answer to part a, which are examples of disruptive, stabilizing or directional selection? c) For human populations living in regions of the world without malaria, do you expect the HS allele to eventually go extinct? Explain.
Sickle cell anaemia: The selective forces that a population experiences can vary by context, especially by geographic place. a) Explain in your own words how natural selection affects the evolution of haemoglobin in humans and how and why the selective pressures differ among human populations. b) For your answer to part a, which are examples of disruptive, stabilizing or directional selection? c) For human populations living in regions of the world without malaria, do you expect the HS allele to eventually go extinct? Explain.
Sickle cell anaemia: The selective forces that a population experiences can vary by context, especially by geographic place. a) Explain in your own words how natural selection affects the evolution of haemoglobin in humans and how and why the selective pressures differ among human populations. b) For your answer to part a, which are examples of disruptive, stabilizing or directional selection? c) For human populations living in regions of the world without malaria, do you expect the HS allele to eventually go extinct? Explain.

Explanation / Answer

a) Natural selection favors the survival of the fittest. In a constant environment, natural selection maintains status quo. If a new variation occurs which is more advantageous than the existing one, natural selection perpetuates the new variation for the evolution of species. In a changing environment, natural selection will favor variations that are better adapted to survive in the changed environment. Therefore, the sickle cell anemia occurs as a result of selective pressure of natural selection in places where malaria is prevalent as a protective mechanism against the disease.

b) Disruptive selection favors both phenotypic extremes and the intermediate phenotypes are lost resulting in bimodal spread. In stabilizing selection, intermediate phenotypes are favored at the expense of both the extreme phenotypes. Directional selection favors one phenotypic extreme which is more beneficial than the other phenotypic extreme.

c) In human population living in regions of the world without malaria, the HS allele is no longer useful for survival. Gradually due to the stabilizing process of natural selection, the HS allele will eventually go extinct.

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