Colour - blindness occurs in

Options

A. Males having colour blind father and normal mother
B. Females having colour blind father and normal mother
C. Females having colour blind father and carrier mother
D. Males have normal father and mother.

Answer

To solve the question regarding color blindness, we need to understand the genetic basis of the condition and analyze the given options step by step.

### 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. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).

2. **Analyzing the Options**:
- We will evaluate each option based on the inheritance patterns of X-linked traits.

3. **Option 1**: Males having a colorblind father and a normal mother.
- The father can only pass on his Y chromosome to his sons. Therefore, the son will inherit the normal X chromosome from his mother. Since he has a normal X, he cannot be colorblind. **This option is incorrect.**

4. **Option 2**: Females having a colorblind father and a normal mother.
- The father will pass on his X chromosome (which is colorblind) to his daughter, and the mother will pass on her normal X chromosome. The daughter will have one colorblind X and one normal X (XcX). She will be a carrier but not colorblind. **This option is incorrect.**

5. **Option 3**: Females having a colorblind father and a carrier mother.
- The father passes on his colorblind X chromosome (Xc), and the mother, being a carrier, can pass on either her normal X (X) or her colorblind X (Xc).
- Possible combinations for the daughter:
- Xc from father and X from mother (XcX) - carrier
- Xc from father and Xc from mother (XcXc) - colorblind
- Therefore, this option can result in a colorblind female. **This option is correct.**

6. **Option 4**: Males having normal father and normal mother.
- Both parents are normal, so they can only pass on normal X and Y chromosomes. Therefore, their son cannot be colorblind. **This option is incorrect.**

### Conclusion:
The correct answer is **Option 3**: Females having a colorblind father and a carrier mother can be colorblind.