A colour blind man marries a woman with normal sight who has no history of colour blindness in her family. What is the probability of their grandsons from the sons being colour blind ?
A colour blind man marries a woman with normal sight who has no history of colour blindness in her family. What is the probability of their grandsons from the sons being colour blind ?
The correct option is D
Explanation of the correct option:
In the given question, a colour blind man was found to marry a woman with normal sight who has no history of colour blindness in her family. The colour blind man's genotype is XcY and his wife is XX . This couple would have carrier daughters and normal sons, as colour blindness follows a criss-cross pattern of inheritance. That is from father to daughter and mother to son. In this case, since the mother is normal, daughters are not affected but they are carriers.
We can see that the sons wouldn't carry the affected gene and hence their families will not be affected.
This because the children of all the sons would have the normal genotype XX or XY (assuming that the mother is normal). So the probability of their grandson from the sons being colour blind is nil.
Explanation of the incorrect options:
Option A:
- 0.25 probability will come when we will consider all the grandsons from daughters and sons together.
- Hence, in case of grandsons from the sons, this option is invalid.
Option B:
- 0.5 probability will come when we will consider the grandsons of only daughters.
- Hence, in case of grandsons from the sons, this option is invalid.
Option C:
- Probability 1 means all the grandsons will be colourblind.
- But this will not happen. Hence, this option is incorrect.
Final answer: A colour blind man marries a woman with normal sight who has no history of colour blindness in her family. The probability of their grandsons from the sons being colour blind is nil.
The correct option is D
Explanation of the correct option:
In the given question, a colour blind man was found to marry a woman with normal sight who has no history of colour blindness in her family. The colour blind man's genotype is XcY and his wife is XX . This couple would have carrier daughters and normal sons, as colour blindness follows a criss-cross pattern of inheritance. That is from father to daughter and mother to son. In this case, since the mother is normal, daughters are not affected but they are carriers.
We can see that the sons wouldn't carry the affected gene and hence their families will not be affected.
This because the children of all the sons would have the normal genotype XX or XY (assuming that the mother is normal). So the probability of their grandson from the sons being colour blind is nil.
Explanation of the incorrect options:
Option A:
- 0.25 probability will come when we will consider all the grandsons from daughters and sons together.
- Hence, in case of grandsons from the sons, this option is invalid.
Option B:
- 0.5 probability will come when we will consider the grandsons of only daughters.
- Hence, in case of grandsons from the sons, this option is invalid.
Option C:
- Probability 1 means all the grandsons will be colourblind.
- But this will not happen. Hence, this option is incorrect.
Final answer: A colour blind man marries a woman with normal sight who has no history of colour blindness in her family. The probability of their grandsons from the sons being colour blind is nil.
