The gene for sickle-cell anaemia in homizygous condition is lethal and produces sickle cell trait in heterozygous carrier. Explain.

Explanation

1. The disease of sickle cell anaemia ils caused by a gene `Hb^(S)`.
2. The normal characters are due to dominant gene `Hb^(A)`.
3. Heterozygous `Hb^(A)//Hb^(S)` are carriers and show mild anemia.
They are said to have sickle-cell trait. Otherwise such individuals are normal.
4. Homozygous `Hb^(S)//Hb^(S)` are lethal combination and hence they die due to fatal anaemia.