What are variations of genes for a single trait called?

Variations of genes for a single trait are known as alleles. Alleles are different forms of a gene that can exist at a specific locus on a chromosome, and they contribute to the diversity of traits seen in a population. For example, a gene that determines flower color in pea plants may have alleles for purple or white flowers. When an organism inherits different alleles from its parents for a trait, this genetic variation is what leads to the expression of different phenotypes.

The other options do not fit this definition. Lycopods refer to a group of vascular plants and are unrelated to genetic traits. Gametes are the sex cells (sperm and egg) that carry alleles but are not variations of genes themselves; rather, they are the vehicles for transmitting alleles to the next generation. Isomers are compounds with the same chemical formula but different structural arrangements, which pertains more to chemistry than to genetics. Therefore, alleles are the correct term for variations of genes affecting a particular trait.