A couple has three children, two without sickle cell anemia and one with sickle cell anemia. The mother has sickle cell anemia as well, while the father does not. Make and defend a claim as to how this couple could have children with and without sickle cell anemia.

Explanation:

The sickle cell allele is recessive. Hence, in order for any child of the couple to have sickle cell anemia, such a child will have to inherit an affected allele each from the two parents. This means that both the father and the mother must have affected alleles in their genotypes. In other words, two sickle cell alleles are required for the abnormality to manifest.

Let us assume that the sickle cell allele is represented by S and the normal allele is represented by A.

Now, it is established that the mother has sickle cell anemia, her genotype would be SS. The father does not have sickle cell, his genotype can either be AA or AS.

Assuming the genotype of the father is AA:

          SS   x   AA

      AS   AS   AS   AS

All the children would be normal in this case.

Assuming that the genotype of the father is AS

           SS    x    AS

      AS   SS   AS   SS

50% of the children would have sickle cell while the remaining 50% would be normal.

Therefore, in order to produce children with sickle cell, the father has to be AS, otherwise, he has to be AA.

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