Question

Attempt any TWO of the following: 

‘The gene for sickle cell anaemia in homozygous condition is lethal and produces sickle cell trait in heterozygous carrier’. Explain. 

Answer 1

Sickle cell trait describes a condition in which a person has one abnormal allellof the hemoglobin beta gene (is hetrozygous), but does not display the severe symptoms of sickle cell disese that occur in a person who has two copies of that allele (is hemozygous). Those who are heterozygous for the sickle cell allele produce both normal and abnormal hemoglobin (the two alleles are condominant with respect to the actual concentration of hemoglobin in the circulating cells).
Sickle cell disease is a blood disorder wherein there is a single amino acid substitution in the hemoglobin protein of the red blood cells which causes these cells to assume a sickle shape, especially when under low oxygen tension. Sickling and sickle cell disease also confer some resistance to malaria parasitization of red blood cells, so that individuals with sickle-cell trait (heterozygotes) have a selective advantage in environments where malaria is present.