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Sickle cell anaemia: The selective forces that a population experiences can vary by context, especially by...

Sickle cell anaemia: The selective forces that a population experiences can vary by context, especially by geographic place.

a. Explain how natural selection affects the evolution of haemoglobin in humans and how and why the selective pressures differ among human populations. Use Africa and Europe as examples of human populations, give genotypes and explain selective pressures.

b. Is natural selection on haemoglobin in African populations best described as disruptive, stabilizing or directional selection?

c. Is natural selection on haemoglobin in Australian populations (no malaria) best described as disruptive, stabilizing or directional selection?

d. For human populations living in Australia (no malaria), do you expect the Hs allele to eventually go extinct? Explain why or why not.

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Expert Solution

a) Explain how natural selection affects the evolution of hemoglobin in humans. and how and why the selective pressures differ among human populations. Use Africa and Europe as examples of human populations, give genotypes, and explain selective pressures.

Natural selection always affects the evolution of Hb in humans as this occurs when there are differences in fitness among members of a population.so that's why some people pass these genes to the next generations and this may change the allele frequencies. sometimes natural selection can favor harmful alleles.

there are three genotypes of sickle cell anemia.

  • AA which shows normal Hb but no fitness as not resistant to malaria
  • AS which shows normal Hb with resistance to sickle cell anemia and also resistant to malaria because of heterozygous alleles.
  • SS This is sickle cell Hb which is resistant to malaria but prone to sickle cell anemia.

natural selection helps to pass the AS genotype in the next generation as this is resistant to malaria. this genotype population able to survive. and this population keeps S in alleles.

evolution showed that individuals who carried the sickle-cell trait were resistant to malaria. here the African population has sickle cell anemia gene in which natural selection had acted to increase the prevalence of traits that protect individuals from malaria. unlike Europe where there are so no or fewer cases of sickle cell anemia and also it is free from malaria is eliminated.

here mainly it shows the selective advantage of the heterozygous allele AS. Given that persons carrying the homozygous SS( HbSS) genotype had almost no chance to reproduce and can die from this. natural selection helped keep AS genotype in population which show resistance to malaria and which shoed increased fitness to sickle cell anemia. this is how selection pressure worked.

gladiator answered 2 years ago
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