How many different phenotypes could exist for this trait suppose only one gene with two alleles determines

No. of phenotypes expressed by a gene = (2n + 1)

Explanation:

It is a basic mathematical function that predicts the average number of phenotypes expressed by a gene. In the above function, n represents the number of genes that are expressing themselves.

the diploid number of chromosomes is sometimes represented by the symbol 2n. for the fruit fly, the diploid number is 8, which can be written as 2n = 8, where n represents twice the number of chromosomes in a sperm or egg cell.