Whether a fly has white or red eyes is due to alleles at a single locus. it is thus a or trait.

The correct answer is "qualitative, discrete".

Explanation:

A qualitative or discrete trait is defined as a characteristic that have no intermediate features, and is often the result of genetic alleles at a single locus. For instance, if the form the seeds of pea could be either round or wrinkled, but not with intermediate forms. This is the case of the fly that has white or red eyes, but does not have pink eyes or other colors in between.