A human male who is hemizygous for a gene gives rise to

Options

A. brown eyes
B. phenylketonuria
C. colour-blindness
D. cystic fibrosis

Answer

To solve the question regarding a human male who is hemizygous for a gene, we need to understand the concept of hemizygosity and how it relates to genetic disorders.

### Step-by-Step Solution:

1. **Understanding Hemizygosity**:
- In humans, males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).
- A male is said to be hemizygous for genes located on the X chromosome because he has only one copy of the X chromosome. This means that any gene located on the X chromosome will be expressed if it is present, regardless of whether it is dominant or recessive.

2. **Identifying the Disorders**:
- The question lists various disorders, including color blindness, phenylketonuria, cystic fibrosis, and brown eyes.
- Color blindness is an X-linked recessive disorder, meaning it is associated with a gene on the X chromosome. If a male has the allele for color blindness on his single X chromosome, he will express the disorder.
- Phenylketonuria and cystic fibrosis are autosomal recessive disorders, meaning they are located on non-sex chromosomes (autosomes) and require two copies of the defective gene (one from each parent) for the disorder to manifest.

3. **Conclusion**:
- Since the question specifies a human male who is hemizygous for a gene, the only disorder that he would express with one defective allele is color blindness.
- Therefore, the correct answer to the question is that a human male who is hemizygous for a gene gives rise to color blindness.

### Final Answer:
A human male who is hemizygous for a gene gives rise to **color blindness**.