Question

colour blindness in human is sex linked recessive trait .if two individuals with normal colour vision have a colour blind son, what will be the genotype of parents.
a)XcXc and XcY
b)XCXc and XCY
c)XcXc and XCY

Answer 1

The colour blind ‘gene’ is carried on one of the X chromosomes. Since men have only one X chromosome, if his X chromosome carries the colour blind ‘gene’ (X) he will be colour blind (XY). A woman can have either:-

(i) two normal X chromosomes, so that she will not be colour blind or be a carrier (XX),

(ii) or, one normal X and one colour blind carrying X chromosome, in which case she will be a carrier (XX), or rarely

This is the answer:

(iii) she will inherit a colour blind X from her father and a colour blind X from her mother and be colour blind herself (XX). She will pass on colour blindness to all of her sons if this is the case.