The paradox of low genetic variability between different domestic flies

The paradox of low genetic variability between different domestic flies

In the smoldering and often dirty world of the humble domestic fly, there is a clear division between the males of the species (the Domestic Musca). Although it is not a civil war, there are differences, no doubt, between the men of the north and those who come from the south. Discovering why these differences appear in the genetic sequences of northern and Southerners is key to understanding nothing less than sex determination, but there is an essential paradox: genetic difference is trivial.

"We are seeing a physical difference and that tells us that we will see a genetic difference that results in physical difference, but we find very few genomic differences," says Richard Meisel, assistant professor of biology and biochemistry at UH, on the September cover article of the magazineGenetics. Physical disturbance suggests that temperature is a significant difference between the two types of males.

"We want to know how these things that are so physically different in an evolutionaryly significant way can have such a similar genetics," Meisel said.

The heart of Meisel's work is the determination of sex. Scientists understand it relatively well in humans: a gene on the Y chromosome initiates the process of male development, and the process is the same in almost all mammals. But outside the class of mammals, the determination of sex operates differently. The domestic fly has a substantial variation in the way the man/woman decision is made. There are two common ways male development can be initiated, and they differ in their geographic distributions. One male determining variant predominates in the northern latitudes, and the other is more common in the south.

And that's why

Although tiny, the difference between the two types of flies is the position of the Y chromosome in the gene sequence.

"If Y is the reason, then there has to be something genetic about that chromosome that allows that reason," Meisel said. "It is difficult for us to understand how that trivial amount of difference in genome sequence causes this variation," Meisel said, adding that evidence indicates that natural selection maintains the determination of sex in the house.

Together with graduate student Jae Hak Son, Meisel examined the chromosomes and conducted mRNA sequencing experiments to measure gene expression in male houses carrying different Y chromosomes. The scan allows you to identify candidate phenotype differences between males over which natural selection can act to maintain variation in gender determination.

"Our results suggest that if natural selection keeps polygenic sex determination at home through gene expression differences, the phenotypes under selection are likely to depend on a small number of genetic goals," he said.