Question

What is the inheritance of color blindness of both parents having normal vision but mother having a recessive gene for color blindness?
A. Son - 50%; Daughter - nil
B. Son -100%; Daughter - nil
C. Son - nil; Daughter - 100%
D. Son - nil; Daughter - nil

Answer 1

Hint: The chromosome responsible for this color blindness is the sex chromosome. Based on the inheritance by pedigree analysis, we can find the chance of getting color blindness from the parents.

Complete answer:
One of the X-linked recessive disorders is color blindness. To cause the disorder (${ X }^{ c }{ Y }$) the affected gene in males of one copy in each cell. To cause the disorder (${ X }^{ c }{ X }^{ c }$) the affected gene in females of two copies in each cell. But the Females with the heterozygous (${ X }^{ c }{ X }$) for this trait act as a normal but serve as a carrier of the disease. By the above question, we can state that the female is a carrier for color blindness (${ X }^{ c }{ X }$) and the father is normal (XY). The carrier mother for color blindness will inherit the disease to 50% sons (${ X }^{ c }{ Y }$) but the daughter will have a normal vision of 100%.

Additional Information: Colour blindness is a hereditary (inherited) condition that is very common. Colour blindness usually passes from parents to the offspring. The sex chromosome is the 23 chromosome in which the color blindness color usually is Red/green color blindness and it is passed from mother to son. The 23 rd chromosome is called a sex chromosome as it helps in determining the sex.
So, the correct answer is ‘Son - 50%; Daughter – nil’.

Note: Most often color blindness is a recessive trait on the X chromosome which is inherited. This is known in genetics as X linked recessive inheritance. Therefore, the disease tends to affect men more than women (8% men, 0.5% women).