Sarah Petrosky to speak

Sarah Petrosky - Rebeiz Lab

"Genetic Heterogeneity in Drosophila melanogaster Pigmentation"

Friday, February 26, 2021

12:10 PM

Virtual Zoom seminar

Abstract:

The connection between genotype and phenotype is rarely straightforward, especially when considering traits that have recently evolved by natural selection in a population. Most traits are polygenic, with each gene having a subtle effect on phenotype. These causative alleles may not sweep through the entire population: instead of clear “winning” and “losing” alleles, we may find a heterogeneous patchwork of different genes that, when combined, generate similar phenotypes. Fitness-affecting alleles may also experience epistatic effects which mask their influence on phenotype in different backgrounds, generating “cryptic genetic variation”. To explore how genetic heterogeneity and epistasis complicate our picture of evolution in populations, I investigated African populations of Drosophila melanogaster. In these populations, cuticle melanization is broadly correlated with altitude: highland flies are dark relative to lowland populations which display ancestral light coloration. This recurring clinal pattern suggests that highland pigmentation has evolved repeatedly under natural selection. Genetic mapping uncovered that this trait is genetically heterogeneous, as different causative loci underlie melanism of lines from the same population. To validate the candidate genes predicted by genetic mapping and implicate these candidates as causal alleles underlying the dark highland phenotype, I utilized in situ hybridization and reporter assays. in situ hybridization uncovered differential expression of pigment-producing enzymes such as ebony, tan, and yellow between highland and lowland flies, as well as between different isofemale lines from the same highland or lowland population. These results support the hypothesis that highland pigmentation is genetically heterogeneous. Reporter assays demonstrated differences in GFP expression of the upstream regulatory element of yellow, suggesting that genetic changes to this regulatory region may contribute to the highland phenotype. Future work will investigate other candidate genes, their regulatory regions, and potential epistatic interactions that affect the final phenotype.

Date

26 Feb 2021

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