Question

Given below is a picture that shows the magnified blood smear of a patient under a microscope.

1. Name the disease the blood smear is indicative of. Write the symptoms of the disease and its cause.    (1)
2. Explain the inheritance pattern of the disease with the help of a suitable cross.    (2)

Answer 1

1. The blood smear reveals sickle-shaped red blood cells, indicating sickle-cell anaemia.
   Symptoms: Biconcave disc to elongated sickle like RBC, severe anaemia, shortness of breath, etc.
   Substitution of glutamic acid (Glu) with valine (Val) occurs at the sixth position of the beta globin chain in the haemoglobin molecule.
2. Sickle-cell anaemia is an autosomal recessive characteristic that can be passed down from parent to offspring when both spouses carry the gene (heterozygous). This condition is governed by a single allele pair, Hb^A and Hb^s. Hb stands for haemoglobin, and Hb^s is the normal blood genotype. Homozygous individuals for Hb^s (Hb^s Hb^s) exhibit disease phenotype. Heterozygous individuals are carriers of haemoglobin A (Hb^A Hb^s)