A boy is colour blind, in his two sisters one is colour blind and one is carrier (normal). Then who is colour blind in his family

Options

A. Father
B. His grand father and mother
C. Mother
D. His grand father

Explanation

To solve the problem of identifying who is color blind in the family, we will analyze the genetic inheritance pattern of color blindness, which is an X-linked recessive disorder.

### Step-by-Step Solution:

1. **Understanding Color Blindness**:
- Color blindness is caused by a mutation on the X chromosome and is inherited in an X-linked recessive manner. This means that males (XY) are more likely to be affected because they have only one X chromosome. Females (XX) can be carriers if they have one affected X chromosome and one normal X chromosome.

2. **Identifying the Boy's Genotype**:
- The boy is color blind, which means his genotype is XcY (where Xc represents the affected X chromosome). He has one affected X chromosome and a Y chromosome.

3. **Analyzing the Sisters**:
- One sister is color blind, which means her genotype is also XcXc (both X chromosomes are affected).
- The other sister is a carrier, which means her genotype is XcX (one affected X chromosome and one normal X chromosome).

4. **Determining the Mother's Genotype**:
- Since the boy (XcY) and one of his sisters (XcXc) are color blind, we can deduce that the mother must carry at least one affected X chromosome.
- The mother can either be a carrier (XcX) or color blind herself (XcXc). However, since one sister is a carrier and not color blind, the mother's genotype must be XcX (carrier).

5. **Determining the Father's Genotype**:
- The father contributes the Y chromosome to the son and does not pass on an X chromosome. Therefore, the father’s genotype must be XY (normal), as he cannot be color blind (he does not have an affected X chromosome).

6. **Conclusion**:
- In this family, the individuals who are color blind are the boy and one of his sisters. The mother is a carrier, and the father is not color blind.

### Summary of Color Blind Family Members:
- **Color Blind**: The boy (XcY) and one sister (XcXc).
- **Carrier**: The other sister (XcX).
- **Not Color Blind**: The mother (carrier, XcX) and the father (normal, XY).