Question

Study the given pedigree chart for sickle-cell anaemia and select the most appropriate option for the genotypes of parents, $1^{s t}$ child and $3^{r d}$ child in $F_{1}$ generation respectively.

• A. $H b^{A}H b^{S}, \, H b^{A}H b^{A}H b^{A}H b^{A}, \, H b^{A}H b^{S}$
• B. $H b^{A}H b^{S}, \, H b^{A}H b^{S}H b^{A}H b^{A}, \, H b^{A}H b^{A}$
• C. $H b^{A}H b^{A}, \, H b^{A}H b^{S}H b^{A}H b^{A}, \, H b^{S}H b^{S}$
• D. $H b^{A}H b^{S}, \, H b^{A}H b^{S}H b^{A}H b^{S}, \, H b^{S}H b^{S}$

Answer 1

Answer: (D)

Pedigree analysis provides information regarding inheritance of particular traits or diseases and using it we can predict the possibility of appearance of any traits in the new generation. In the given chart, both son and daughter have the recessive trait suggesting it to an autosomal inheritance and not sex-linked. Since, it is not expressed in any of the parent but expressed in the children, the trait is recessive.
Since parents are showing the recessive trait, they are heterozygous having the genotype - $H b^{A}H b^{S}$ for both parents. First child (female) is not affected but one of her son is suggesting that she is carrier with the genotye $H b^{A}H b^{S}$ same as her parents. Also, her husband is not affected suggesting that he is a carrier as well. The third child of the parent is an affected son having the diseases sickle cell anemia. His genotype will be $H b^{S}H b^{S}$ .