The number of phenotypes produced for a given trait depends on

1. the number of genes that control the trait
2. which form of the trait is dominant
3. the allele frequency of the various alleles
4. the relationship of allele frequencies to mendelian ratios
2.

The correct answer for the blank is- 1. The number of genes that control the trait.

Phenotype represents the morphological form or physical characteristic of an individual. It is depicted by the genes ( segment of DNA corresponding to particular proteins, which is responsible for the trait of an individual).

This means that the number of phenotypes produced for a given trait depends upon the the number of genes that control the trait.

For exampe- Polygenic traits are controlled by more than one gene and they produce multiple phenotypes.

These traits depict wide range of variation in them ( such as human traits like height, color of skin).

b is the best answer for this question.