Which of the following genotypes is homozygous dominant? (2 points)
tt
ff
xy
ss

The correct answer is SS.

In the homozygous condition, the two alleles present for the traits are similar. The allele could be either dominant or recessive. the dominant allele are those alleles, which masks the effect of the recessive allele, if present together.

In standard references, the dominant alleles are always denoted in capital letters and the recessive allele is always denoted as the small letters. In the above condition, SS represent two dominant alleles, hence, the SS is a homozygous dominant genotype.