Question

A woman with normal vision, but whose father was colour bind, marries a colour blind man. Suppose that the fourth child of this couple was a boy. This boy -

• A. Must have normal colour vision
• B. May be colour blind or may be normal vision
• C. Will be partially colour blind since he is heterozygous for the colour blind mutant allele.
• D. Must be colour blind

Answer 1

The correct option is B May be colour blind or may be normal vision

Gametes	22A+x	22A+Y
22A+X	22AA+Xx- carrier female	22AA+XY- normal male
22A+x	22AA+xx- diseased female	22AA+xY- diseased male

The woman has normal vision but her father was colour blind so she should be the carrier to the disease as Colour blindness is an X-Linked recessive disorder.

So, the genotype of the woman should be- 22AA+Xx (where 'X' represent normal sex chromosome while 'x' represents colour blinded).

The genotype of man to be colourblind should be: 22AA+xY

So, the cross between 22AA+Xx X 22AA+xY is shown in the table.

The probability of Male child to be colourblind will 50% and the ratio of diseased to a normal male child is 1:1.

So, the correct answer is 'Maybe colour blind or maybe normal vision'.

So the correct option is B.