Question

If individuals with the sickle-cell hemoglobin are selected against, how is it that the mutated hemoglobin gene persists in the human population? Choose the best answer. Individuals with sickle-cell disease (recessive homozygous) are best able to fight off malaria, so the gene persists in malarious areas. The monkey bread tree is not sensitive to temperature. When a non-sickle cell individual (dominant homozygous) mates with an individual with sickle-cell disease (recessive homozygous) the produce heterozygotes and that is how the mutated gene persists in the population. The heterozygous condition confers a benefit; heterozygotes can fight off the parasite that causes malaria in malarious areas.

Answer 1

The answer is 4th option - The heterozygous condition confers a benefit; heterozygotes can fight off the parasite that causes malaria in malarious areas

Sickle cell anemia is an autosomal recessive trait. The two copies of the mutated gene are required to exhibit the sickle cell disease. The individuals with one copy of the mutated gene are carriers and they do not have sickle cell disease. Sickle cell anemia is caused by the mutation in the hemoglobin beta gene. In a population where malaria is common, there will be a high frequency of sickle cell allele. The individuals who are heterozygous for sickle cell trait are resistant to malaria. Individuals who are heterozygous for sickle cell trait have one copy of the normal hemoglobin gene (HbA) and one copy of the sickle cell gene (HbS). In a malarious population, individuals with heterozygous genotype have greater fitness than homozygous genotypes. Through balancing selection, two different alleles are maintained in the population. In the areas where the malaria parasite is present since the heterozygous condition is advantageous, it is not removed by natural selection.