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If both parents of a male child are norm...

If both parents of a male child are normal, what are the chances of the child being colour blind ?

A

It is possible only if father's mother was colour blind

B

It is possible only if mother's father was colour blind

C

It is impossible

D

It is possible even when at the four grandparents had normal vision

Text Solution

AI Generated Solution

The correct Answer is:
To determine the chances of a male child being color blind when both parents are normal, we need to analyze the genetics behind color blindness, which is a sex-linked recessive disorder. ### Step-by-Step Solution: 1. **Understanding Color Blindness**: - Color blindness is primarily caused by a defect in the genes located on the X chromosome. It is a recessive trait, meaning that a person must have two copies of the defective gene to express the trait (in females) or one copy (in males). 2. **Genetic Makeup of Parents**: - In this scenario, both parents are said to be normal. However, it is important to consider that the mother could be a carrier of the color blindness gene. - The father, being male, has one X chromosome and one Y chromosome (XY). Since he is normal, his X chromosome does not carry the color blindness gene (denoted as X^N). - The mother, being female, has two X chromosomes (XX). If she is normal, she could either have two normal X chromosomes (X^N X^N) or one normal and one defective X chromosome (X^N X^c), where X^c represents the color blindness allele. 3. **Possible Genotypes of the Mother**: - If the mother is normal and not a carrier: X^N X^N (no chance of color blindness). - If the mother is a carrier: X^N X^c (there is a chance of passing the color blindness gene to her offspring). 4. **Inheritance Pattern**: - Males inherit their X chromosome from their mother and their Y chromosome from their father. Therefore, a male child will be affected by color blindness if he inherits the X^c chromosome from his mother. - If the mother is a carrier (X^N X^c), there is a 50% chance that she will pass the X^c chromosome to her son. 5. **Conclusion**: - If both parents are normal and the mother is not a carrier, the child cannot be color blind. However, if the mother is a carrier, there is a 50% chance that the male child will be color blind. - Therefore, the chances of the male child being color blind is **50%** if the mother is a carrier. ### Final Answer: The chances of the male child being color blind, assuming the mother is a carrier, is **50%**. ---
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