In the context of genetic disorders, consider the following: A woman suffers from colour blindness while her husband does not suffer from it. They have a son and a daughter. In this context, which one of the following statements is most probably correct?
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UPSC Civil Services preparation
- ABoth children suffer from colour blindness.
- BDaughter suffers from colour blindness while son does not suffer from it.
- CBoth children do not suffer from colour blindness.
- DSon suffers from colour blindness while daughter does not suffer from it.Correct
Explanation
Color blindness is an X linked recessive disorder. This means the gene for color blindness is located on the X chromosome.
A woman has two X chromosomes. For a woman to be color blind, both her X chromosomes must carry the defective gene. Let us denote the affected X chromosome as Xc. So, the mother's genotype is Xc Xc.
A man has one X chromosome and one Y chromosome. Since the husband is not color blind, his genotype is XY.
When they have children:
1. The son receives a Y chromosome from his father and an X chromosome from his mother. Since the mother only has affected Xc chromosomes to give, the son will always be Xc Y. Therefore, the son will be color blind.
2. The daughter receives one X chromosome from each parent. She gets a normal X from her father and an affected Xc from her mother. Her genotype will be X Xc. Because the normal X chromosome is dominant, she will not suffer from color blindness but will be a carrier.
Thus, the son suffers from color blindness while the daughter does not. This makes option D the correct answer.

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