= Drosophila melanogaster rosy
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<Drosophila melanogaster rosy>, usually written `ry`, is a protein-coding <gene> encoding <xanthine dehydrogenase>, an <enzyme> involved in <purine> degradation. FlyBase identifies it as FBgn0003308 and CG7642. The named <gene>, its enzyme product and the visible eye-colour phenotype used in genetic experiments are different levels of description.<Drosophila melanogaster rosy in FlyBase>[General Information and Gene Summary]{ref}
The locus became an informative marker in early <P-element vector> experiments. A 1982 study transferred a wild-type rosy-containing <DNA> fragment into mutant embryos and obtained animals with inherited chromosomal copies and wild-type eye colour. The phenotype made the introduced sequence's function visible; molecular and inheritance measurements established that more than a transient signal had occurred.<Genetic transformation of Drosophila with transposable element vectors by G. M. Rubin and A. C. Spradling>[Abstract, transferred rosy sequence and transformed phenotype]{ref}
As a teaching comparison, two insertions could both restore the marker phenotype while carrying different neighbouring <DNA> or occupying different genomic positions. The shared visible outcome would not establish identity of the complete constructs. A marker therefore helps select or recognize an outcome, while sequencing, mapping and transmission answer additional questions about what was introduced and where it resides.
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