Why is male sex called hemizygous in man and Drosophila?

Explanation

### Step-by-Step Solution:

1. **Understanding Sex Chromosomes**:
- In humans and Drosophila (fruit flies), individuals have sex chromosomes that determine their sex. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).

2. **Definition of Hemizygous**:
- The term "hemizygous" refers to the presence of only one allele for a particular gene in an otherwise diploid organism. This means that for a gene located on the X chromosome, males have only one copy (allele) because they possess only one X chromosome.

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