Overview:

As a geneticist and evolutionary biologist, I am intrigued by a broad array of scientific puzzles. My projects are united by my interest in how new combinations of DNA are created and maintained. My work uses genetics to investigate evolutionary questions such as:
  • How can we better understand gene flow and its effects?
  • How does variation in chromosomal arrangement shape evolution?
  • How does genetic exchange via hybridization and recombination influence adaptation and divergence?
  • How does linkage-disequilibrium shape nucleotide variation through the action of linked selection?​

PROJECTS

Inferring evolutionary processes in admixed populations:

I have recently joined the Goldberg lab, where I plan to work on understanding gene flow, adaptation, and complex demography using population genetics in humans and other primates. My goals include understanding:
  • Adaptive introgression: we aim to understand cases where admixture can facilitate rapid adaptation when alleles introgressed from a source population provide a selective advantage.
  • Population genetics of recently admixed populations: ​we plan to improve our understanding of patterns such as sex-biased admixture and assortative mating in recently admixed populations.

Recombination and inversions:

During my PhD work, one of my primary aims was to understand how chromosomal inversions shape meiotic recombination, the process that shuffles combinations of alleles across loci. Inversions suppress recombination, but we don’t fully understand how and to what extent. Though single-crossover products are prevented within inversion heterozygotes, non-crossover gene conversion (and double crossovers) can still occur. By studying the frequency and distribution of non-crossover gene conversion in inversion heterozygotes, I aimed to improve our understanding of how recombination acts alongside natural selection to influence genome evolution and speciation processes (Korunes & Noor 2017: doi:10.1111/mec.13736).

To better understand the recombination-barrier imposed by inversions, I examined rates of gene conversion in experimental crosses both within Drosophila pseudoobscura and between D. pseudoobscura and its naturally-hybridizing sister species D. persimilis. Through genome-wide empirical analyses of within species and in species hybrids, I observed that gene conversion rates in interspecies hybrids are at least as high as within-species estimates of gene conversion rates, and gene conversion occurs regularly within and around inverted regions of species hybrids, even near inversion breakpoints. This analysis is the first direct empirical assessment of gene conversion rates within inversions of a species hybrid, and these data show that gene conversion has the potential to reduce the efficacy of inversions as barriers to recombination over evolutionary time. For more details on this project, see Korunes & Noor 2019 (doi.org/10.1111/mec.14921).

Linked selection:

Despite the shuffling of alleles via recombination, alleles at neighboring loci often remain non-randomly associated. This non-random association, or linkage-disequilibrium (LD), has evolutionarily important effects both within and between species. I study genetic diversity in Drosophila species with the goal of disentangling how different selective forces at a given locus can affect genetic diversity at neighboring linked loci. By understanding meiotic recombination and linked selection, I aim to address broader questions about how genetic diversity is created and maintained.

The role of introgression in speciation and divergence:

The sister species pair Drosophila pseudoobscura and D. persimilis present an opportunity to dissect an evolutionary history of divergence nuanced by multiple inversions, lineage sorting, and gene flow. In a collaboration with Carlos Machado and Mohamed Noor, I used whole-genome sequence data to re-explore patterns of introgression and divergence in the Drosophila pseudoobscura / D. persimilis system, with strategic use of  an allopatric point of comparison, D. pseudoobscura bogotana (D. p. bogotana), which split from North American D. pseudoobscura (D. p. pseudoobscura) about 150,000 years ago. This investigation presented the opportunity to not only examine the effects of introgression, but also to understand how differences in evolutionary rate among lineages can influence patterns of divergence and tests for introgression. Consideration of ancestral inversion polymorphisms and different evolutionary rates in these populations reveals that recent gene exchange is a major but not the sole driver of variation in overall sequence divergence. Overall, we show that inversions have contributed to divergence patterns between Drosophila pseudoobscura and D. persimilis over three distinct timescales: 1) pre-speciation segregation of ancestral polymorphism, 2) post-speciation ancient gene flow, and 3) recent introgression. These results represent progress towards a more cohesive understanding of how inversions shape gene flow at different timescales along the speciation continuum. This work is available on BioRxiv: doi.org/10.1101/842047.