Question

marla is a known carrier of the sickle - cell allele, while jerry is unsure of his genotype. the couple have three children, and one is diagnosed with sickle - cell disease (scd). what is jerrys genotype? hb^a/hb^s hb^s/hb^s hb^a/hb^a there is not enough information to tell.

Explanation:

Sickle - cell disease (SCD) is a recessive disorder. A carrier has the genotype \(Hb^{A}/Hb^{S}\). For a child to have SCD (\(Hb^{S}/Hb^{S}\)), each parent must contribute an \(Hb^{S}\) allele. Marla (\(Hb^{A}/Hb^{S}\)) can contribute an \(Hb^{S}\) allele. Since one child has SCD (\(Hb^{S}/Hb^{S}\)), Jerry must also be able to contribute an \(Hb^{S}\) allele. The genotype \(Hb^{A}/Hb^{A}\) cannot contribute an \(Hb^{S}\) allele. The genotype \(Hb^{S}/Hb^{S}\) would mean Jerry has SCD (but the problem doesn't state he has symptoms, but in terms of allele contribution for the child's genotype), and \(Hb^{A}/Hb^{S}\) (carrier) can contribute an \(Hb^{S}\) allele. However, the key is that to get an \(Hb^{S}/Hb^{S}\) child, both parents need to pass on \(Hb^{S}\). Since Marla is \(Hb^{A}/Hb^{S}\) (passes \(Hb^{S}\) half - the time), Jerry must have at least one \(Hb^{S}\) allele. Among the given options \(Hb^{A}/Hb^{S}\) (carrier) can pass \(Hb^{S}\) (50% chance in gamete formation) and \(Hb^{S}/Hb^{S}\) (100% chance of passing \(Hb^{S}\)). But if Jerry was \(Hb^{A}/Hb^{A}\), no \(Hb^{S}\) could be passed. Since there is a child with \(Hb^{S}/Hb^{S}\), Jerry must have an \(Hb^{S}\) allele.

Answer:

\(Hb^{A}/Hb^{S}\)