Different forms of a gene located at the same locus of chromosomes are called

Options

A. Multiple alleles
B. Polygenes
C. Nucleus
D. Chlorplast

Answer

### Step-by-Step Solution:

1. **Understanding Genes and Chromosomes**:
- Genes are segments of DNA that carry genetic information. They are located on chromosomes, which are rod-like structures found in the nucleus of cells.

2. **Defining Locus**:
- The term "locus" refers to the specific position or location of a gene on a chromosome. The plural form of locus is "loci."

3. **Identifying Different Forms of a Gene**:
- Different forms of a gene that occupy the same locus on a chromosome are known as alleles. Alleles can vary in their sequence and can result in different traits or characteristics.

4. **Understanding Multiple Alleles**:
- When there are more than two forms of a gene at the same locus, these are referred to as "multiple alleles." For example, the ABO blood group system in humans is determined by multiple alleles (I^A, I^B, and i) at a single locus.

5. **Conclusion**:
- Therefore, the answer to the question is that different forms of a gene located at the same locus of chromosomes are called **multiple alleles**.