Suppose there is a vial containing a single generation of flies from a cross. There is an interesting phenotype where many individuals have abnormally long hairlike bristles, sensory organs extending from the dorsal thorax, as opposed to the short wirelike wild-type bristles among the other siblings. References state that this mutant has a dominant mutation called Suave (Su) and that the phenotype of flies that are heterozygous or homozygous for Su appear phenotypically identical. Which fly should be crossed to a Suave male from this vial in order to generate progeny that help determine the male's genotype?

Which fly should be crossed to a Suave male from this vial in order to generate progeny that help determine the male's genotype?