A research team from the University of Texas at Arlington, led by Jeffery Demuth, associate professor of biology and Heath Blackmon, a Ph.D. student, assembled a database of 4724 beetle species’ karyotypes and found extensive variation in sex chromosome systems, allowing them to explain Y chromosome loss with the “fragile Y” hypothesis.
The hypothesis states that recurrent selection to reduce recombination between the two sex chromosomes can lead to the evolution of small PARs, or pseudoautosomal regions (sequences of nucleotides located on the tips of the X and Y-chromosomes allowing for X/Y recombination during meiosis in males), increasing the loss of the Y chromosome during meiosis. In species where no PARs exist there is a decreased probability of Y chromosome loss.
The hypothesis could reveal new insights about the evolution of sex chromosomes, since these are key players in human development, with errors resulting in several important human diseases, such as hemophilia.
Although previous research regarding sex chromosomes has been conducted in either mammals or Drosophila (fruit flies), beetles are the most diverse group on the planet, with over 350,000 species discovered and described. The results found by these scientists can be extrapolated to the mammal world. As such, while placental mammals need PARs for X/Y recombination, marsupials do not, resulting in several Y chromosome loses in placental mammals (e.g. rodents) but not in marsupials (e.g. kangaroos).
While traditionally seen as underrated genetic material that is lost throughout evolution, the stability or loss of the Y chromosome in beetles populations can confirm that the patterns found in mammals hold true even in groups separated by hundreds of millions of years.