Mormann, B. | Search bioRxiv

bioRxiv2026

Natural genetic variation spans all predicted Rh5/Rh6 expression phenotypes in Drosophila R8 photoreceptors

Standing genetic variation is immediately available to selection, but how broad a range of phenotypes it can produce remains unknown for many traits. Here we address this question using the mutually exclusive Rhodopsin 5 (Rh5) and Rhodopsin 6 (Rh6) expression pattern in Drosophila R8 photoreceptors, a neuronal differentiation readout that permits enumeration of a finite set of predicted qualitative phenotypic changes. Wild flies and wild-derived inbred lines from the Drosophila Genome Reference Panel 2 (DGRP2) showed extensive variation in Rh5/Rh6 expression, including shifts in the relative abundance of Rh5- and Rh6-expressing R8s, Rh5/Rh6 co-expression, and loss of Rh5 or Rh6. Among 205 DGRP2 lines, we observed examples spanning all eight predicted qualitative phenotype categories. We also identified causal coding and regulatory variants, including alleles of sevenless, Rh5 and Rh6, and an intronic deletion in melted. These results show that standing natural variation can span the full predicted range of qualitative phenotypes in this system.

genetics↗

bioRxiv2017

Natural variation in stochastic photoreceptor specification and color preference in Drosophila

Each individual perceives the world in a unique way, but little is known about the genetic basis of variation in sensory perception. Here we investigated natural variation in the development and function of the color vision system of Drosophila. In the fly eye, the random mosaic of color-detecting R7 photoreceptor subtypes is determined by stochastic expression of the transcription factor Spineless (Ss). Individual R7s randomly choose between SsON or SsOFF fates at a ratio of 65:35, resulting in unique patterns but consistent proportions of cell types across genetically identical retinas. In a genome wide association study, we identified a naturally occurring insertion in a regulatory DNA element in the ss gene that lowers the ratio of SsON to SsOFF cells. This change in photoreceptor fates shifts the innate color preference of flies from green to blue. The genetic variant increases the binding affinity for Klumpfuss (Klu), a zinc finger transcriptional repressor that regulates ss expression. Klu is expressed at intermediate levels to determine the normal ratio of SsON to SsOFF cells. Thus, binding site affinity and transcription factor levels are finely tuned to regulate stochastic on/off gene expression, setting the ratio of alternative cell fates and ultimately determining color preference.

developmental biology↗