What do we call the different versions of a gene?

The term used to describe different versions of a gene is "alleles." Alleles are variants that arise due to mutations and can result in different traits or characteristics being expressed in an organism. For example, a gene that determines flower color in plants may have several alleles that produce red, white, or blue flowers.

In the context of genetics, while chromosomes are structures that contain genes, they do not refer to variations within those genes. Genotypes represent the genetic makeup of an individual regarding specific traits, which can include one or more alleles but do not refer directly to the variations themselves. Phenotypes, on the other hand, are the observable characteristics or traits of an organism that result from the interaction of its genotype with the environment. Therefore, "alleles" is the correct term for the different versions of a gene.