To solve this problem, we need to understand the concept of multiple alleles.$\newline$Multiple alleles refer to the presence of more than two allelic forms of a gene.$\newline$Let's analyze the options to determine where multiple alleles are present:$\newline \bullet$Option 1: On different chromosomes.$\newline$ - Alleles of a gene are not located on different chromosomes. They are different forms of the same gene.$\newline \bullet$Option 2: At different loci on the same chromosome.$\newline$ - Alleles of a gene occupy the same locus, not different loci.$\newline \bullet$Option 3: At the same locus of the chromosome.$\newline$ - This is correct. Multiple alleles are different forms of a gene that exist at the same locus on a chromosome.$\newline \bullet$Option 4: On non-sister chromatids.$\newline$ - Alleles are not specifically located on non-sister chromatids. They are found at the same locus on homologous chromosomes.$\newline$Therefore, the correct answer is Option 3: At the same locus of the chromosome.