Question

A family has a history of colour blindness. During a genetic testing, it was found that the mother is a carrier of colour blindness (X^C X) and the father has normal vision (XY). What is the probability of their sons being colour blind?

• A. 25%
• B. 50%
• C. 75%
• D. 0%

Hint:

Remember, since colour blindness is a recessive sex-linked trait, a son can only inherit it if he receives the X^C chromosome from his mother and the Y chromosome from his father.

Answer 1

The Correct Option is B

Step 1: Understanding the inheritance of colour blindness.
Colour blindness is a sex-linked recessive trait carried on the X chromosome. In this case, the mother is a carrier of colour blindness (X^C X), meaning one of her X chromosomes carries the colour blindness gene, while the other carries the normal vision gene. The father has normal vision (XY), meaning his X chromosome carries the normal vision gene and his Y chromosome determines male sex.
Step 2: Determining possible combinations.
The mother can pass on either her X^C chromosome (carrying the colour blindness gene) or her normal X chromosome (X). The father will pass on either his X chromosome or his Y chromosome. The possible combinations for their sons (who must inherit the Y chromosome from their father) are: - X^C (from mother) and Y (from father) → Colour blind son. - X (from mother) and Y (from father) → Normal vision son.
Step 3: Probability calculation.
Since the mother has a 50% chance of passing on the X^C chromosome and a 50% chance of passing on the normal X chromosome, the probability of their son inheriting colour blindness is 50%. Final Answer: 50%.