The propagation of every animal on the planet is the result of sexual activity between males and females of a given species. But how did things get this way? Why two sexes instead of one? Why are sperm necessary for reproduction and how did they evolve?
These as-yet-unresolved issues fascinate Timothy Karr, a developmental geneticist and evolutionary biologist at Arizona State University’s Biodesign Institute. To probe them, he uses a common fruit fly, Drosophila melanogaster-an organism that has provided science with an enormous treasure-trove of genetic information.
“My research focuses on the evolution of sex and in gamete function,” Karr says. “I focus primarily on the sperm side of the sexual equation. I’m interested in how they originated and how they are maintained in populations.”
Karr’s current study, in collaboration with researchers at the University of Chicago, recently appeared in the journal BMC Biology. The study reexamines an earlier paper that analyzed the sex chromosomes of fruit flies during spermatogenesis-the process that produces mature sperm from germ cells.
While the previous paper, by Lyudmila M Mikhaylova and Dmitry I Nurminsky, argued against the silencing of sex-linked genes on the X chromosome in Drosophila during meiosis-a process referred to as Meiotic Sex Chromosome Inactivation (MSCI) -the reanalysis presented by Karr suggests MSCI is indeed occurring.
The work sheds new light on the evolution of sperm structure and function, through an analysis of Drosophila genes and gene products. As Karr explains, the research has important implications for humans as well: “The more direct, biomedical aspect is that when we learn about the function of a gene that encodes a protein in Drosophilasperm, we can immediately see if there’s a relationship between these genes and their functions and known problems with fertility in humans.” Read full article.
