The sickle cell version of the gene that causes sickle cell disease is recessive. Suppose that two parents with no symptoms have a child with sickle cell disease. What genes did the child inherit from the parents?

The genes that the child inherited from the parents is the SS gene

Explanation:

The genetic composition of the haemoglobin genotype is given by two gene variants; A which is dominant and S which is recessive. As such, an individual can be AA, AS or SS. Individuals that are AA and AS do not show traits of the disease, but SS individuals have sickle cell anaemia.

From this example, since both parents have no symptoms and their child have sickle cell, their genotypes most likely were AS and AS. Let me show you how:

           A              S

A        AA            AS

S       AS              SS

From the cross above, there is a 1 in 4 chance that if both parents were AS, their child will be SS. Any other composition from the parents will not produce an SS offspring. Hence the genes that the child inherited from the parents is the SS gene.

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