question_answer

A couple whose sons are colour blind with AB blood group, identify the parent from the following.

A) Mother colourblind with blood group-A and father normal with blood group-B

B)  Mother normal with blood group-A and father colourblind with blood group-B

C)  Mother colourblind with blood group-B and father normal with blood group-B

D)  Mother normal with blood group-A and father colourblind with blood group-B

Correct Answer: B

Solution :

Colour blindness is caused by recessive sex-linked gene carried by X-chromosome. So.  male, one recessive gene is sufficient for its expression, ie, \[({{X}^{c}}Y)\]but female needs two recessive genes\[({{X}^{c}}{{X}^{c}})\]for the expression of colour blindness. Mother will colourblind with blood group-A and father normal with blood group-B.                 So, All the sons will be colourblind with blood group-AB.