An entomologist crossed pure-breeding fruit flies (Drosophila melanogaster) that had red eyes with pure-breeding fruit flies that had brown eyes.
All of the offspring in the first generation (F1F_1F1) had red eyes.
The entomologist then allowed these F1 F_1\,F1 offspring to interbreed.
In the second generation (F2F_2F2), some offspring had red eyes and others had brown eyes.
Explain how this cross shows that some alleles are present but not expressed in the phenotype of an organism.
