If we cross Surface fish (have eyes and are not albino) with fish from Cave Scarlet, the F1 progeny have eyes and are not albino. If we backcross these F1 Surface/Scarlet hybrids to Scarlet cavefish, 50% of the progeny are albino and 50% are not albino. In terms of the eye phenotype, there is a broad range of eye phenotypes extending from no eyes like the original Scarlet population to complete eyes like surface fish (with varying degrees of eye formation in between