Question

A normal woman whose father was colorblind is married to a normal man. The sons would be
A.75% colorblind
B.50% colorblind
C.All normal
D.All colorblind

Answer 1

Colour blindness is a recessive sex-linked disorder in which the person cannot differentiate between different colors.

Complete answer:
-Color blindness is an X-linked recessive disorder. Only the daughters can receive the affected X chromosomes from the father and hence an affected father can inherit the disorder to the female child. Hence in the given question although it is said that the woman is normal, she is still a carrier of the color blindness gene because her father was a color-blind person and the man in the given question is also normal. Suppose X is a normal gene and X' is a color-blind gene.

The cross can be shown as:
Parents: XX' × XY

Parents	X'	X
X	X'XCarrier girl	XXNormal girl
Y	X'YCarrier boy	XYNormal boy

Hence only 50% of the sons are color blind rest of the sons are normal.

Option B: only 50% of sons are color blind and the rest of the sons will be normal. Therefore, this is the correct option.

All other options are irrelevant.

Hence, the correct answer is option (D)

Note: The gene of color blindness is located on one of the X chromosomes of an affected individual. Hence, it is more commonly seen in males as compared to females because males have only one X chromosome and if the color blindness gene is present on that X chromosome, the individual will be color blind whereas females have two X chromosomes, and if only one chromosome has the color blindness gene then that female will be a carrier for this disorder.