In genetic inheritance, what term refers to different forms of a gene?

The term that refers to different forms of a gene is alleles. Alleles are specific versions of a gene that arise through mutations and can produce variations in traits. For each gene, an individual inherits two alleles—one from each parent. These variations can lead to different phenotypes, which are the observable characteristics resulting from the interaction of the genotype (the genetic makeup) with the environment.

Chromosomes are structures within cells that contain DNA, and while they carry genes, they are not different forms of a gene themselves. Phenotypes refer to the expressed traits or characteristics that result from the interaction of alleles, and genotypes describe the genetic constitution (the specific alleles present) of an individual. Thus, while all of these terms are related to genetics, only "alleles" specifically indicates the different forms a gene can take.