Question

Ram and Asha were a married couple. They had four children - one of these children had sickle cell anemia whereas the other four children did not show symptoms. Ram and Asha did not show symptoms of sickle cell anaemia. The trait for sickle cell anaemia is not linked to the sex chromosomes.

(a) Is this disease caused by a dominant or recessive trait? Why?

(b) If the child that had sickle cell anaemia got married to a person without a mutation in the sickle cell anaemia gene, what percentage of their children would have sickle cell anaemia? Show the cross.

OR

Identify the genetic composition of the sickle cell anaemia trait in Asha and Ram and use that to predict the genetic composition in the other four children who did not show symptoms that Ram and Asha had.

Answer 1

(a) It is recessive. 

If it was dominant, it would have appeared in more than 1 child.

(b) 

	s	s
S	Ss	Ss
S	Ss	Ss

None of the children would have sickle cell anaemia/0% children would have sickle cell anaemia. 

OR 

Ram's genetic composition: Ss

Asha's genetic composition: Ss 

Four possible genetic compositions in children: SS, Ss, Ss, ss.

So, the composition of the other three children would either be Ss or ss.