Multiple alleles are present

Options

A. at different loci on the same chromosome
B. at the same locus of the chromosome
C. on non-sister chromatids
D. on different chromosomes

Answer

**Step-by-Step Text Solution:**

1. **Understanding Multiple Alleles**: Multiple alleles refer to the presence of more than two allelic forms of a gene. While a typical gene may have two alleles (dominant and recessive), multiple alleles indicate that there are three or more variations of that gene.

2. **Location of Alleles**: The question asks where these multiple alleles are located. The options provided include:
- Different loci on the same chromosome
- The same locus on the chromosome
- On non-sister chromatids
- On different chromosomes

3. **Identifying the Correct Option**: For multiple alleles, they must be located at the same locus on a chromosome. This means that all the variations of the gene are found at the same position on the chromosome, differing only in their allelic forms.

4. **Example of Multiple Alleles**: A classic example of multiple alleles is the ABO blood group system in humans. In this system, there are three alleles: I^A, I^B, and i. These alleles determine the blood type (A, B, AB, or O) and are all located at the same locus on chromosome 9.

5. **Conclusion**: Based on the understanding of multiple alleles and their location, the correct answer to the question is that multiple alleles are present at the same locus on the chromosome.

**Final Answer**: Multiple alleles are present at the same locus on the chromosome.

---