Elucidation of the sex-determination pathways in an organism with monogenic sex determination. Meaghan L Pimsler¹, Sing-Hoi Sze², Corbin D Jones³, Jeffery K Tomberlin¹, Aaron M Tarone¹. 1) Entomology, TAMU, College Station, TX; 2) Computer Science and Engineering, TAMU, College Station, TX; 3) Biology Department, UNC, Chapel Hill, NC.

   Research has shown sex-specific differences in gene expression in Diptera, an examples of which is Sex-lethal (Sxl) in Drosophila. The standard system in flies is one in which males are heterogametic and males and females are produced in approximately even proportions. However, Chrysomya rufifacies (Diptera: Calliphoridae) exhibits monogenic sex determination with single sex offspring clutches and homomorphic sex chromosomes. As there are no known morphological differences in the immature stages, genetic markers for quick sex-specific screening of larvae will be useful to look at differences between males, male-producing females, and female-producing females. Our objective was to identify markers of the three types of adults using transcriptomics. A single male and female were isolated together. Upon oviposition, the two adults were collected for subsequent RNA extraction after the progeny had eclosed and the progenitor female had been identified. RNA were sequenced with Illumina HiSeq and the transcriptomes were assembled with ASplice. Predicted transcripts were compared with information in the FlyBase database to identify homologous genes and predict functions. Transcripts were assembled that shared homology with four genes identified from Drosophila sex-determination pathways: Sxl, da, dsx, and fru. Male and female isoforms were also assembled for Sxl and dsx. On average, only about ten percent of the genes were differentially expressed between males and females and about sixty percent were male biased. In comparison, only about one percent of the transcriptome was statistically different between female types and about eighty percent of them were male-producer biased. This is surprising as the current model of sex determination in this species is that the female producers are heterozygote dominant for a product that is incorporated during gametogenesis and determines the sex of the offspring.