Anopheles gambiae ASEMBO sex chromosome evolution

Anopheles rDNA are located on the sex chromosomes, often exclusively on the X chromosome, as for the Anopheles gambiae G3 and Anopheles arabiensis Dongola strains. This exclusively X-linked rDNA locus was used to develop a transgenic An. Gambiae G3 strain (?2-Ppo1) that expresses the I-Ppo1 endonuclease during male meiosis, which targets and cleaves An. gambiae 28S rDNA (Galizi et al., 2014). The rDNA locus of An. gambiae ASEMBO strain is located in both the X- and Y-chromosomes. To test whether recombination can occur between the rDNA loci of the An. gambiae sex chromosomes, Introgression of the An. gambiae YASEMBO into the transgenic meiotic rDNA-cleaving An. gambiae ?2-Ppo1 G3 strain was perfrmed. Backcrossing of the transgenic male offspring over multiple generations was conducted to selectively cleave the YASEMBO rDNA, while uncleaved XG3 chromosome was introduced every generation through backcrossing of wildtype An. gambiae G3 females. Sequencing was then conducted to assess whether after 24 generations of rDNA cleavage, this had resulted in repair, deletions, or other mutations of rDNA copies.