"One of the things my lab is interested in is the evolution of genome architecture and the constraints under which that architecture evolves," Demuth said. "The sex chromosomes are particularly interesting because they are obviously a key developmental switch, and errors resulting in too many or too few copies result in several important human diseases."
Besides the XY combination associated with mammals, there is a ZW combination for birds and some other animals. There are cases in nature where both the Y and the W get lost through evolution creating XO and ZO pairs.
Traditionally, scientists have explained the loss by saying that the Y chromosome must not contain enough important genetic information and so it is dispensable. In that process, any important genes move from the Y to another chromosome and sex determination takes a different route. Some scientists have even theorized that the human Y chromosome only has about another 10 million years before all genes on the Y chromosome will be lost.
To find out if there was more at work in Y chromosome loss, Blackmon and Demuth assembled a database of karyotypes, a kind of chromosome map, for 4,724 beetle species, also known as the order Coleoptera. In that large field, they found what they called "substantial variation in sex chromosome systems." Then, they zeroed in on the two largest suborders of the beetle family - Polyphaga, which has a relatively stable Y chromosome, and Adephaga, which has a less stable Y.
The resulting fragile Y hypothesis focuses on differences in how X and Y chromosomes are divided when sperm is produced. Many species, including humans, have spaces on the X and Y chromosomes where the two chromosomes recombine or mingle. This is called the "pseudoautosomal region," or PAR. In the species that have a PAR, it is ce
|Contact: Traci Peterson|
University of Texas at Arlington