Answer:
Two phenotypes.
Step-by-step explanation:
When there is a single gene trait and it shows a simple dominant-recessive pattern then it will result in two phenotypes. As the name suggests, a single gene trait is a trait which is controlled by only one gene.
For example, consider a trait Tallness which is a single gene trait and the two alleles for this gene are T and t where T is dominant and t is recessive. The different phenotypes in different allelic combinations has been shown below -
TT - Tall
Tt - Tall
tt - dwarf
Thus we see here that only two phenotypes Tall and dwarf are present for the all possible genotypes.