Fine-scale evolutionary genetic insights into Anopheles gambiae X-chromosome

Understanding the genetic architecture of individual taxa of medical importance is the first step for designing disease preventive strategies. To understand the genetic details and evolutionary perspective of the model malaria vector, Anopheles gambiae and to use the information in other species of local importance, we scanned the published X-chromosome sequence for detail characterization and obtain evolutionary status of different genes. The telocentric X-chromosome contains 106 genes of known functions and 982 novel genes. Majorities of both the known and novel genes are with introns. The known genes are strictly biased towards less number of introns; about half of the total known genes have only one or two introns. The extreme sized (either long or short) genes were found to be most prevalent (58% short and 23% large). Statistically significant positive correlations between gene length and intron length as well as with intron number and intron length were obtained signifying the role of introns in contributing to the overall size of the known genes of X-chromosome in An. gambiae. We compared each individual gene of An. gambiae with 33 other taxa having whole genome sequence information. In general, the mosquito Aedes aegypti was found to be genetically closest and the yeast Saccharomyces cerevisiae as most distant taxa to An. gambiae. Further, only about a quarter of the known genes of X-chromosome were unique to An. gambiae and majorities have orthologs in different taxa. A phylogenetic tree was constructed based on a single gene found to be highly orthologous across all the 34 taxa. Evolutionary relationships among 13 different taxa were inferred which corroborate the previous and present findings on genetic relationships across various taxa.