Use a punnett square in fruit flies, red eyes (r) are dominant to pink eyes (r). what is the phenotypic ratio of a cross between a heterozygous male and a pink-eyed female

The gene R controls the eye color: R is dominant allele and r is recessive allele.

Genotypes for the red-eyes are RR (dominant homozygous) and Rr (heterozygous).

Genotype for the pink eyes is rr (recessive homozygous).

If we cross a heterozygous male and a pink-eyed female:

P1: Rr  x  rr

F1: Rr Rr rr rr

The phenotype ratio in the offspring will be 1:1 (red eyes : pink eyes).