Genes Relocated Between Drosophila Chromosome Arms Evolve Under Relaxed Selective Constraints Relative to Non-Relocated Genes
Gene duplication creates a second copy of a gene either in tandem to the ancestral locus or dispersed to another chromosomal location. When the ancestral copy of a dispersed duplicate is lost from the genome, it creates the appearance that the gene was “relocated” from the ancestral locus to the derived location. Gene relocations may be as common as canonical dispersed duplications in which both the ancestral and derived copies are retained. Relocated genes appear to be under more selective constraints than the derived copies of canonical duplications, and they are possibly as conserved as single-copy non-relocated genes. To test this hypothesis, we combined comparative genomics, population genetics, gene expression, and functional analyses to assess the selection pressures acting on relocated, duplicated, and non-relocated single-copy genes in Drosophila genomes. We find that relocated genes evolve faster than single-copy non-relocated genes, and there is no evidence that this faster evolution is driven by positive selection. In addition, relocated genes are less essential for viability and male fertility than single-copy non-relocated genes, suggesting that relocated genes evolve fast because of relaxed selective constraints. However, relocated genes evolve slower than the derived copies of canonical dispersed duplicated genes. We therefore conclude that relocated genes are under more selective constraints than canonical duplicates, but are not as conserved as single-copy non-relocated genes.
KeywordsGene relocation Gene duplication Gene expression RNAi Selective constraints
We thank members of the Meisel lab at the University of Houston and Andy Clark’s lab at Cornell University for assistance with the RNAi experiments. Mariana Wolfner kindly supplied the bam-Gal4 line, which was originally produced in Margaret Fuller’s laboratory. Erin Kelleher and multiple anonymous reviewers provided valuable feedback that improved this manuscript. We were supported by start up funds from the University of Houston to RPM and a University of Houston Summer Undergraduate Research Fellowship to LZ.
- Gromko MH, Gilbert DG, Richmond RC (1984) Sperm transfer and use in the multiple mating system of Drosophila, In: Smith RL (ed) Sperm competition and the evolution of animal mating systems, Academic Press, New York, pp. 371–426Google Scholar
- Kondrashov F, Rogozin I, Wolf Y, Koonin E (2002) Selection in the evolution of gene duplications. Genome Biol 3(research0008):1Google Scholar
- Muller HJ (1940) Bearings of the ‘Drosophila’ work on systematics. In: Huxley J (ed) The new systematics. Clarendon Press, Oxford, pp 185–268Google Scholar
- R Core Team (2015) R: a language and environment for statistical computing. R Foundation for Statistical Computing, ViennaGoogle Scholar