Recombination rate evolution and its impact on genomic architecture
- Recombination occurs when chromosomes exchange genetic material when being put into gametes, which is the main reason why no two offspring from the same set of parents look exactly alike. Mechanistically, recombination is necessary to stabilize chromosomes during meiosis, but too many recombination events can lead to birth defects/disease. Evolutionarily, recombination helps to shuffle beneficial alleles onto common genetic backgrounds, facilitating the efficacy of selection, but too much recombination can break down these associations. Until the 1980s, population geneticists assumed rates of recombination were uniformly distributed across the genome, however we now know this not to be the case. Recombination rates are highly variable across taxa and genomes. I am interested in quantifying that variability and understanding how selection and/or mutation drive ubiquitous correlations between nucleotide diversity/divergence and GC-content.
Understanding why recombination rates correlate with nucleotide diversity within species
Nearly 20 years ago, an analysis of recombination rate variation was shown to correlate with genetic diversity within species. This fundamental paper was key in pointing out what has become a ubiquitous finding in many study systems. Scientists have tried to determine whether selection or mutation is driving this correlation by examining nucleotide divergence between species. This test has had contradictory results depending on the study system and/or the scale at which recombination is assayed. By continuing to assay fine-scale recombination rates in many biological systems, we can finally understand why recombination rates correlate so commonly with nucleotide diversity, but not always with nucleotide divergence.
Recombination rates between species correlate when compared at broad-scales
Once two species are no longer interbreeding, recombination rates are free to evolve in different directions, but mechanistic constraints may limit how much this is allowed to change. I am what types of genetic features lead to divergence in recombination rates between species. In humans and chimpanzees, scientists have found that recombinations strongly correlate when examined at the 1 Megabase or larger scale, whereas they are highly divergent when compared at the 1 kilobase or smaller scale. One possible reason for changes in local recombination rates is nucleotide divergence at sequence motifs which bind to recombination machinery. Fine-scale recombination rate studies in many biological systems can also inform scientists as to which sequence motifs are most predictive of recombination rate variation. This approach has proved useful in humans in identifying novel transcription factors involved in the process of meiotic recombination.
See publications on this topic:
L.S. Stevison and M.A.F. Noor. 2010. Genetic and evolutionary correlates of fine-scale recombination rate variation in Drosophila persimilis. Journal of Molecular Evolution. 71(5): 332-345.
Fitzpatrick, C.F., Stevison, L.S. and M.A.F. Noor. 2009. Fine-scale crossover rate and interference along the XR-chromosome arm of Drosophila pseudoobscura. Drosophila Information Service, 92:27-29.
Stevison, L.S. and M.A.F. Noor. 2009. Recombination Rates in Drosophila. In: Encyclopedia of Life Sciences, Chichester: John Wiley & Sons, Ltd.