Each gene trait is influenced or controlled by two or three phenotypes. What determines the number of phenotypes for a given trait. Evolution And Classification Warm Ups And Interactive Notebook Pages Interactive Notebooks Evolution Interactive The number of phenotypes produced for a given trait depends on how many genes control the traitWhat determines number of phenotypes for a traitThe number of phenotypes fo. . A single-gene trait is. A geneticist can provide probabilities for certain genotypes and phenotypes before the breeding takes place. The number of phenotypes produced for a given trait depends on how many genes control the trait. On the other hand a polygenic trait is influenced by two. The genetic contribution to the phenotype is called the genotype. Some traits are largely determined by the genotype while other traits are largely determined by environmental factors. Homozygous individuals expr...