I’m a PhD candidate in Stony Brook University’s genetics program who studies theoretical population genetics and Drosophila genetics.  The effects of genes are often buffered by other genes, and organisms with the same genotype need not have the same fitness.  Consequently, one can ask: What are the evolutionary ramifications of the fact that genes occur within organisms?  With this in mind, my thesis work involves the study of incomplete penetrance and synthetic incompatibilities.  Using wild-caught D. melanogaster and extracted-X lines, we have found a naturally occurring mutation that causes an incompletely penetrant balloon-wing phenotype to occur.  As part of my thesis, I am studying how various factors (such as environment, sex, and genetic background) affect the penetrance of this trait.  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!).

Figure 1. Two landscape metaphors: Wright’s fitness landscape for constant and stochastic fitness scenarios and Waddington’s epigenetic landscape under canalized and non-canalized scenarios.

Figure 2. Uniform pedigrees for different types of inbreeding. Males are represented by squares, females with circles. The proband is indicated with an arrow. Diagonal lines correspond to trans-generational matings. A. Sibling mating, no growth of pedigree size. B. 1st cousin mating, linear growth of pedigree size. C. 2nd cousin mating, geometric growth of pedigree size. D. Half-sibling mating, linear growth of pedigree size. E. Half-1st cousin mating, geometric growth of pedigree size. F. Uncle-niece mating, no growth of pedigree size. G. Trans-generational outbred mating, geometric growth of pedigree size.

 

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.  2008a.  Detecting Selection-Induced Departures from Hardy-Weinberg Proportions. submitted

Lachance, J.  2008b.  A Fundamental Relationship Between Genotype Frequencies and Fitnesses. Genetics 180:1087-93

Lachance, J.  2008c.  Inbreeding, the Pruning of Family Trees, and the Most Recent Common Ancestor of Humanity. submitted

Lachance, J.  2008d.  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.