Species are defined as entities capable of "exchanging genes." Understanding what causes or prevents gene exchange between groups is therefore fundamental to understanding the process of species formation ("speciation") and the origin of biodiversity on our planet. For over 13 years now, the Noor lab has pursued many projects investigating the effects of chromosomal inversions on gene exchange between hybridizing species for over a decade, particularly in Drosophila pseudoobscura and D. persimilis. Specifically, if two species differ by one or more chromosomal inversions, large blocks of the genome cannot flow between species even when some of the hybrids are fertile (see abstracts). This decrease in gene flow appears to be directly related to the absence of crossing over that occurs within the inverted regions. Many lines of evidence support this conclusion-- e.g.,, when comparing two species, the inverted regions often show much higher divergence than non-inverted (colinear) regions, suggesting a lack of recombination and introgression.
What's perhaps unexpected is that, although single-crossovers are potentially prevented from being recovered from inversion heterozygotes, double-crossovers and noncrossover gene conversion should be still allow for exchange between inversion types. Nonetheless, inverted regions consistently show this higher divergence, implying little (if any) recombination and introgression. We have found that double-crossovers happen at far, far lower rates than expected in inverted regions in species hybrids, and we're trying to understand this by comparing rates using inter- and intra-species inversion heterozygotes. We've also recently got extensive whole-genome sequence (WGS) data from various intra- and inter-species crosses to examine rates of gene conversion.
This work is fundamentally important to understanding why species persist as distinct entities even when they hybridize and the specific nature of how chromosomal inversions may facilitate this process.
Plasticity and selection on recombination rate variation
Since 2006, our lab has pursued various projects examining the amount, genetic causes, and evolutionary consequences of recombination rate variation among regions of the Drosophila genome (see abstracts). Our past research identified that, contrary to earlier dogma, fine-scale variation in recombination does exist among regions of the Drosophila genome. We also found that this variation correlates strongly with amount of nucleotide diversity, and we found evidence this variation is related to the spread of advantageous alleles within species.
We previously only looked at variation AMONG STRAINS only
briefly, and we only studied recombination rate in idealized
laboratory conditions. We now extend our earlier work to answer
the following specific questions. We are examining variation AMONG NATURAL POPULATIONS in recombination rate, and testing
whether this variation may be adaptive.
Recombination rate is also plastic in response to environmental
conditions. This sets up a situation wherein the recombination
rates experienced under extreme conditions in nature may be
maladaptive. We are further testing for "plasticity
compensation", wherein populations have adapted to mitigate
detrimental environmentally induced recombination rates.
This last project is particularly important given effects of
global climate change on our planet. Further, recombination is
fundamental to many genetic and evolutionary processes, yet no
studies have explored whether natural populations have adaptive
differences in recombination rate, particularly in response to
Our research team and collaborators have always been interested in biology education, including developing various new educational activities and resources. Two particularly unusual projects include developing a kit for studying natural selection in Drosophila marketed by Carolina Biological Supply and helping with the design of an iOS app for learning about genetics and evolution. We continue to be interested in the development of such activities and resources, including doing proper assessment of their efficacy in classrooms.