Insect body color is an easily assessed and visually engaging trait that is informative on a broad range of topics including speciation, biomaterial science, and ecdysis. Mutants of the fruit fly Drosophila melanogaster have been an integral part of body color research for more than a century. As a result of this long tenure, backlogs of body color mutations have remained unmapped to their genes, all while their strains have been dutifully maintained, used for recombination mapping, and part of genetics education. Stemming from a lesson plan in our undergraduate genetics class, we have mapped sable1, a dark body mutation originally described by Morgan and Bridges, to Yippee, a gene encoding a predicted member of the E3 ubiquitin ligase complex. Deficiency/duplication mapping, genetic rescue, DNA and cDNA sequencing, RT-qPCR, and two new CRISPR alleles indicated that sable1 is a hypomorphic Yippee mutation due to a mdg4 element insertion in the Yippee 5’-UTR. Further analysis revealed additional Yippee mutant phenotypes including curved wings, ectopic/missing bristles, delayed development, and failed adult emergence. RNAi of Yippee in the ectoderm phenocopied sable body color and most other Yippee phenotypes. Although Yippee remains functionally uncharacterized, the results presented here suggest possible connections between melanin biosynthesis, copper homeostasis, and Notch/Delta signaling; in addition, they provide insight into past studies of sable cell nonautonomy and of the genetic modifier suppressor of sable.

Tandem gene duplicates are important parts of eukaryotic genome structure, yet the phenotypic effects of new tandem duplications are not well-understood, in part owing to a lack of techniques to build and modify them. We introduce a method, Recombinase-Mediated Tandem Duplication (RMTD), to engineer specific tandem duplications in vivo using CRISPR and recombinases. We describe construction of four different tandem duplications of the Alcohol Dehydrogenase (Adh) gene in Drosophila melanogaster, with duplicated block sizes ranging from 4.2 kb to 20.7 kb. Flies with the Adh duplications show elevated ADH enzyme activity over unduplicated single copies. This approach to engineering duplications is combinatoric, opening the door to systematic study of the relationship between the structure of tandem duplications and their effects on expression.

Tandem gene duplicates are important parts of eukaryotic genome structure, yet the phenotypic effects of new tandem duplications are not well-understood, in part owing to a lack of techniques to build and modify them. We introduce a method, Recombinase-Mediated Tandem Duplication (RMTD), to engineer specific tandem duplications in vivo using CRISPR and recombinases. We describe construction of four different tandem duplications of the Alcohol Dehydrogenase (Adh) gene in Drosophila melanogaster, with duplicated block sizes ranging from 4.2 kb to 20.7 kb. Flies with the Adh duplications show elevated ADH enzyme activity over unduplicated single copies. This approach to engineering duplications is combinatoric, opening the door to systematic study of the relationship between the structure of tandem duplications and their effects on expression.