Question

A colourblind man has a colourblind sister but a normal brother than phenotype of its parents is [CPMT 1993]
A) Father colourblind and mother normal
B) Father normal and mother colourblind
C) Father and mother both are colourblind
D) Father and mother both are normal

Answer 1

correct answer is A.

Answer 2

If a colorblind man has a a colourblind sister and normal brother than phenotype of the parents is father colourblind and mother is normal.

● This is because the gene which codes for colour blindness is located on X chromosome.

● Here both boy and girl are colourblind as X chromosome they got is from father.

● This can be proved by the last choice that one boy is normal as his X chromosome is from mother and Y chromosome is from father.