Question

A colourblind man, both of whose parents had normal vision and whose paternal and maternal grandparents had normal vision, probably inherited the gene for color blindness from his
A)Maternal or paternal grandmother
B)Maternal or paternal grandfather
C)Father
D)Mother

Answer 1

Hint: Colour blindness is X-linked recessive trait. It mostly happens in the males and is rarely seen in females. The person who is colour blind is unable to differentiate between red-green colour. This is due to the defect in the cone cells of the eye.

Complete answer:
To solve this question, we must know about the inheritance of colour blindness.

Color Blindness is caused due to X recessive gene. It occurs mostly in males as the male is heterozygous so an X recessive colourblind($x_c$ gene can cause colour blindness. In females two copies of recessive genes are required to cause color blindness ($x_c$$x_c$. The heterozygous females can act as carrier but are not colourblind.
According to the question, the parents are not colourblind. This means that the father is not the carrier. And the maternal and paternal grandfather cannot be the carriers. (Since the carrier males are itself colour blind)
If Grandmother is the carrier, then the generation would be represented as
Grandmother gene- X$x_c$
Grandfather gene-XY

	X	$x_c$
X	XX	$Xx_c$
Y	XY	$x_cY$

The grandmother will have one colour blind male, one normal male and female and a carrier daughter.

If the carrier daughter marries a normal male then the off springs would be

	X	$x_c$
X	XX	$Xx_c$
Y	XY	$x_cY$

The gene must have transmitted through the mother or maternal grandmother.

Hence, the correct answer is option (D)

Note: The color blindness which is caused due to hereditary has no cure. It remains the same throughout the lifetime. It can only be passed from generation to generation in which the females will be the carrier.