Zoology - Principles of Inheritance and Variation Question with Solution | TestHub

Sickle cell anemia

- It is an autosomal recessive disease.

- This disease is controlled by a pair of alleles -${\mathrm{H}\mathrm{b}}^{\mathrm{A}}$(normal dominant allele) and${\mathrm{H}\mathrm{b}}^{\mathrm{S}}$(affected recessive allele).

- Both male and female have either of the three genotypes :

$1.$${\mathrm{H}\mathrm{b}}^{\mathrm{A}}\mathrm{ }{\mathrm{H}\mathrm{b}}^{\mathrm{A}}$- Normal phenotype.

$2.$${\mathrm{H}\mathrm{b}}^{\mathrm{A}}\mathrm{ }{\mathrm{H}\mathrm{b}}^{\mathrm{S}}$- Normal phenotype. For a heterozygous individual, there are 50% chances of transferring the affected allele to next progeny.

$3.$${\mathrm{H}\mathrm{b}}^{\mathrm{S}}\mathrm{ }\mathrm{ }{\mathrm{H}\mathrm{b}}^{\mathrm{S}}$- Diseased phenotype.

- In this disease, due to single base substitution (GAG to GUG), Glutamic acid (Glu) at 6^thposition of the$\beta$-globin chain of the haemoglobin molecule is substituted by Valine (Val).

- Under low oxygen tension, RBC changes its shape to a elongated sickle like structure due to the polymerization of the affected haemoglobin molecule.