A couple had two sons, one was colour blind while the other wasn't. They also had a colour blind daughter. Which statement about this couple is true?

Options

A. Husband is colour blind but wife is not
B. Husband is normal and wife is colour blind
C. Husband and wife both are colour blind
D. Husband and wife both are normal

Answer

To solve the question regarding the couple and their children with color blindness, we need to analyze the genetic inheritance of color blindness, which is a sex-linked recessive trait. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Genetics of Color Blindness
Color blindness is a recessive trait linked to the X chromosome. This means that males (XY) are more likely to express color blindness because they have only one X chromosome. Females (XX) can be carriers if they have one normal X chromosome and one affected X chromosome.

### Step 2: Identify the Traits of the Children
The couple has:
- Two sons: One is color blind and the other is not.
- One daughter: She is color blind.

### Step 3: Determine the Father's Genotype
Since one son is color blind, the father must have the color blind trait. Therefore, the father's genotype is:
- X^hY (where X^h represents the color blind allele).

### Step 4: Determine the Mother's Genotype
The mother must be a carrier because:
- She has a color blind daughter (who must inherit one affected X from her).
- She must also have a normal X to pass on to the son who is not color blind.

Thus, the mother's genotype is:
- X^HX^h (where X^H represents the normal allele).

### Step 5: Analyze the Children’s Genotypes
From the parents' genotypes:
- The color blind son (X^hY) receives the X^h from the mother and Y from the father.
- The normal son (X^HY) receives the X^H from the mother and Y from the father.
- The color blind daughter (X^hX^h) receives X^h from both parents (one from the father and one from the mother).

### Step 6: Conclusion About the Couple
Based on the analysis:
- The father is color blind (X^hY).
- The mother is a carrier (X^HX^h).

Thus, the correct statement about this couple is: "The husband is color blind, but the wife is not (she is a carrier)."

### Summary of the Correct Statement
- The husband is color blind, and the wife is a carrier.

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