Different molecular forms of the same gene are called alleles.

Here's why:

* Genes: Genes are segments of DNA that contain the instructions for building and maintaining an organism. They are located on chromosomes.

* Alleles: Alleles are alternative forms of a gene. They occupy the same locus (position) on homologous chromosomes. The differences in their DNA sequence can lead to variations in the traits they code for.

* Example: The gene for eye color has multiple alleles. One allele might code for blue eyes, another for brown eyes, and another for green eyes.

So, when you see a gene with different molecular forms, you know you're looking at different alleles.