In flies, red eyes (r) are dominant to brown eyes (r). a heterozygous fly is crossed with homozygous recessive fly.
what percentage of offspring will have brown eyes?

50%  of offspring will have brown eyes

Explanation:

A heterozygous individual will have the genotype Rr while an individual who is homozygous recessive will have the genotype rr. A cross between the two will result in offspring with phenotype Rr and rr in the ratio of 1 : 1. This can be observed from the Punnet square attached.  The same is the case for the phenotype. The ration of brown eyes to red eyes will be approximately 1 : 1

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