Question

A colour blind man marries a normal woman whose father was colour blind. What percentage of children is expected to be colour blind?

• A. $25\%$
• B. $50\%$
• C. $75\%$
• D. $100\%$

Answer 1

Answer: (B)

$50\%$

Color blindness is specifically linked to defects within the x chromosome. For color blindness to be present all x chromosomes within an individual have to be affected, and since men only have one X chromosome and women have 2, the chances of men being impacted are exponentially higher.
However, in this case, it would seem that due to the genetic inheritance of the mother the chances of their child being color blind would be approximately 50% because each parent is a carrier. However, the chances of inheriting a colorblind X chromosome would be twice as likely for a female child. Below is how I broke this scenario down, where the lower case x represents the affected X chromosome.
F: xY M: xX
xx—-Female child (color blind)
xX—Female Child (not color blind but a carrier)
Yx—Male Child (Color Blind)

YX—Male Child (not color blind and not a carrier)

So, the correct answer is '50%'.