In multiple allelism, multiple alleles are present:

The correct option is D At the same locus of the chromosome

Multiple alleles are present at the same locus of chromosome. In multiple alleles, three or more alternative forms of a gene (alleles) that can occupy the same locus. A classical example of multiple alleles is found in ABO blood group system of humans. Despite the multiple alleles of any gene, an individual possess and can have only two alleles at a time.