The genetic basis of morphological evolution in Drosophila

• Main Author: Arif, Saad
• Published: Oxford Brookes University 2013
• Subjects: 572.838
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616291

Understanding the evolution of morphological traits requires knowledge of the genetic basis of variation in those traits. This includes fundamental questions such as, but not limited to, how many genetic changes are involved in producing the observed differences? What is the relative magnitude of effect contributed by each change? Are the changes in coding or regulatory regions of the genome? Several studies over the past decade have shed light on these questions; however, the number of such studies remains limited. Here 1 present two case studies on the genetic basis of morphological differences for two different traits at two different evolutionary scales: within species variation in the size of the ' naked valley' (NV, a trichome-less patch on adult Drosophila legs), and between species variation in eye size and face width. My investigations relied on unbiased methods of associating phenotype to genotype, specifically Quantitative Trait Loci (QTL) analysis, fine-scale mapping and then functional analysis of candidate genes where applicable. I found a single genetic region (QTL) associated with intraspecific (within D. melanogaster) variation in the NV. This region was further narrowed down to - 25 kilobases (kb) using fine-scale recombination mapping. Functional analysis of genes within this region revealed that, the microRNA, mir-92a, affects trichome development. Sequence conservation within the functional region of the microRNA suggests that changes in cis-regulatory sequences of mir-92a may be responsible for the observed differences. I also mapped interspecific differences, between D. simulans and D. mauritiana. in eye size and face width to two QTL of moderate to large effect for each trait. Moreover, there was no positional overlap in QTL for these two traits. In contrast to patterns of natural variation, where both traits exhibit pervasive negative correlation, my result indicates that both traits retain a genetic capacity for independent evolution. Additionally, using an introgression approach 1 further refined the location of a major QTL for eye size to a region of 2 Mb that contains several genes known to affect eye size.