Two allelic genes are situated on

The correct option is "two homologous chromosomes".

To understand why this is correct, let's break down the concepts of genes, alleles, and chromosomes step-by-step:

1. What are Alleles?
An allele is an alternative form of a gene. For any given gene, there can be different versions that determine distinct traits (for example, a gene for eye color might have an allele for brown eyes and another allele for blue eyes). Because sexually reproducing organisms inherit one set of chromosomes from each parent, they possess two alleles for each gene.

2. What are Homologous Chromosomes?
Homologous chromosomes are pairs of chromosomes (one maternal and one paternal) that are similar in shape, size, and gene arrangement. They carry the same genes in the same relative positions, known as loci (singular: locus).

3. The Position of Alleles:
Since allelic genes are simply different versions of the same gene, they must control the same trait and occupy the exact corresponding position (locus) on a pair of chromosomes. Because homologous chromosomes contain the same genes at matching locations, the two allelic genes are situated on the two homologous chromosomes—one allele on the maternal chromosome and the other on the paternal chromosome.

4. Why Other Options are Incorrect:
- Same chromosomes: Alleles of the same gene do not sit side-by-side on a single chromosome.
- Two non-homologous chromosomes: Non-homologous chromosomes carry entirely different genes governing different traits, so they cannot host alleles of the same gene.
- Any two chromosomes: This is too broad and incorrect, as alleles are specifically restricted to matching locations on homologous pairs.