Thesis (Ph. D.)--University of Rochester. Department of Biology, 2018.
During meiosis, sexually reproducing eukaryotes exchange genetic material via recombination
and segregate homologous chromosomes into gametes. Surprisingly, some genes involved in
meiotic recombination and chromosomal segregation experience frequent evolutionary turnover.
Growing evidence suggests selfish genetic elements— DNA entities that promote their own
transmission at the expense of other genes in the genome— are a significant evolutionary force
driving rapid molecular evolution at genes involved in an otherwise conserved biological
process. The research in this dissertation integrates classical, molecular, and population genetics
to study the evolution of recombination rates and biased chromosomal segregation in Drosophila.
First, in Chapters 2-4, I focus on the evolution of recombination rates in Drosophila. In Chapter 2,
I perform an evolutionary screen to identify a meiosis gene with a history of recurrent positive
selection that might contribute to differences in the rate of crossing over between two closely
related Drosophila species. I then use a transgenic approach to show this gene, mei-217/mei-218,
mediates the species differences in the rate and patterning of crossing over. In Chapter 3, I use
further transgenic analyses to functionally dissect mei-217/mei-218 to determine which gene
regions control the species differences in crossing over. In Chapter 4, I explore the long-term
molecular evolution of mei-217/mei-218 and find evidence for frequent positive selection during
the phylogenetic history of Drosophila. I find that mei-217/mei-218 wildtype alleles of two
additional Drosophila species have also functionally diverged in their control of crossing over.
I speculate that recurrent bouts of adaptive functional evolution at mei-217/-218 might reflect a
history of coevolution with selfish genetic elements. Next, in Chapter 5, I turn to the evolution of
a meiotic drive system, Segregation Distorter, that causes biased segregation in Drosophila
melanogaster. I use molecular and population genetic tools to investigate the age, geographic
origins, and population dynamics of Segregation Distorter chromosomes. I find that despite its
stable frequency, Segregation Distorter chromosomes experience frequent selective sweeps and
replacement events.