A colourblind man marries a daughter of colourblind father, then in the offsprings :-

Options

A. All sons are colourblind
B. All daughters are colourblind
C. Half sons are colourblind
D. No daughter is colourblind

Answer

To solve the problem of a colorblind man marrying a daughter of a colorblind father, we need to understand the genetics behind color blindness, which is an X-linked recessive trait.

### Step-by-Step Solution:

1. **Understanding Color Blindness**:
- Color blindness is an X-linked recessive disorder. This means that the gene responsible for color blindness is located on the X chromosome, and the condition manifests in individuals who have two copies of the recessive allele (in females) or one copy (in males).

2. **Genotypes of the Parents**:
- The colorblind man will have the genotype X^cY, where X^c represents the X chromosome carrying the color blindness allele.
- The daughter of a colorblind father will inherit one X chromosome from her father (X^c) and one X chromosome from her mother. Assuming the mother is normal (not colorblind), the daughter will have the genotype X^cX (carrier).

3. **Possible Gametes**:
- The colorblind man can only pass on his X^c chromosome or his Y chromosome to his offspring.
- The daughter can pass on either her X^c chromosome or her normal X chromosome (X).

4. **Punnett Square Analysis**:
- We can set up a Punnett square to determine the possible genotypes of the offspring:
- The father (X^cY) can contribute either X^c or Y.
- The mother (X^cX) can contribute either X^c or X.

| | X^c (from mother) | X (from mother) |
|-------|--------------------|------------------|
| X^c (from father) | X^cX^c (colorblind daughter) | X^cX (carrier daughter) |
| Y (from father) | X^cY (colorblind son) | XY (normal son) |

5. **Offspring Genotypes**:
- From the Punnett square, we can see the possible offspring:
- 1 daughter with genotype X^cX^c (colorblind)
- 1 daughter with genotype X^cX (carrier)
- 1 son with genotype X^cY (colorblind)
- 1 son with genotype XY (normal)

6. **Conclusion**:
- The offspring will consist of:
- 50% sons (1 colorblind, 1 normal)
- 50% daughters (1 colorblind, 1 carrier)
- Therefore, the correct answer to the question is that half of the sons are colorblind.

### Final Answer:
- **Half of the sons are colorblind**.