I’m a PhD candidate in Stony Brook University’s genetics program who studies theoretical population genetics and Drosophila genetics. There’s something truly neat about being able to explore the big ideas of evolutionary biology with mathematical rigor. However, it’s also important to empirically test these ideas, and Drosophila melanogaster (what with its cool phenotypes and long history as a model organism) is an ideal system for this. In addition, evolutionary theory can also be applied to human genomic data.
The effects of genes are often context-dependent, and organisms with the same genotype need not have the same fitness. Because of this, I seek to answer the following question: How does the organismal context of a gene affect its evolutionary trajectory? With this in mind, my thesis work involves studying incomplete penetrance and synthetic incompatibilities.
Incomplete penetrance refers to the situation where some individuals with a particular genotype do not exhibit the expected phenotype. Using wild-caught D. melanogaster and extracted-X lines, we have found a naturally occurring mutation that causes wing vesicles. As part of my thesis, I am studying how various factors (such as environment, sex, and genetic background) affect the penetrance of this trait.
Synthetic incompatibilities involve two otherwise neutral alleles that result in sterility or lethality when present in the same individual. These epistatic interactions are important for speciation, as they result in Dobzhansky-Muller incompatibilities. In the True lab we are also interested in the idea that genomes can be considered co-adapted gene complexes. I am characterizing X-autosome synthetic incompatibilities in D. melanogaster and extending analytic theory of this phenomenon.
In addition to a genuine love of teaching, I’m an avid reader of both fiction and nonfiction. I’ve written a number of book reviews for the Quarterly Review of Biology, and have dabbled in science fiction writing (including a piece that managed to get published in Nature!).
Additional projects:
•As part of team (including Roman Yukilevich, Fumio Aoki, and my advisor John True), I assisted in the modeling the long-term adaptation of genetic networks. Interestingly, we found that epistasis qualitatively changes evolutionary trajectories.
•I am also interested in how long it takes for all of humanity to share a common ancestor. Using a mix of biparental coalescent theory and graph theory, I have looked at the impact of inbreeding on this estimate. Surprisingly, Fibonacci-constants arise from inbred pedigrees.
•While sample sizes needed to detect significant departures from Hardy-Weinberg proportions can be quite large, natural selection leaves an interesting footprint on genotype frequencies. Specifically, geometric mean heterozygote frequency divided by geometric mean homozygote frequency equals two times the geometric mean heterozygote fitness divided by geometric mean homozygote fitness. When this genotypic ratio is applied to data from the International HapMap Project, population-specific patterns are found.
Publications:
Lachance, J. and J. R. True. 2009. Synthetic incompatibilities in Drosophila melanogaster: X-autosome interactions, geography, and Haldane’s Rule. In preparation.
Lachance, J. 2009. Inbreeding, the Pruning of Family Trees, and the Most Recent Common Ancestor of Humanity. Journal of Theoretical Biology. Accepted.
Lachance, J. 2009. Detecting Selection-Induced Departures from Hardy-Weinberg Proportions. Genetics Selection Evolution 41:15.
Lachance, J. 2008. A Fundamental Relationship Between Genotype Frequencies and Fitnesses. Genetics 180: 1087-1093.
Lachance, J. 2008. Subject to Change. Nature 454:916.
Yukilevich, R., J. Lachance, F. Aoki, and J. R. True. 2008. Long-Term Adaptation Of Epistatic Genetic Networks. Evolution 62:2215-2235.
