What do you call one version or form of a trait?

One version or form of a trait is called an allele  

An allele is an alternative form of a gene that is situated at a given locus (position) on a specific chromosome. Alleles determine recognizable traits that can be transmitted from parents to offspring through sexual reproduction. In multi-cellular organisms that possesses two copies of each chromosome (diploid organism), two alleles forms the individual's genotype. When allele pairs are identical, they are said to be homozygous, while when they are different, they are heterozygous.

it's     c       this is a cell (b) with a nucleus (c) containing dna (a). the dna is organized into chromosomes (d). a section of the chromosome that codes for a trait is called a gene (e).