On dosing and compensating
Drosophila flies are born with four pairs of chromosomes in each of their cells. It is the genetic heritage they receive from their genitors. Three of these pairs are simply two versions of the same chromosome, as in two copies of chromosomes 2, 3 and 4. The first pair, however, represents the sex chromosomes - of which there are two, X and Y. Female fruit flies receive an X chromosome from both parents, while male fruit flies receive an X chromosome from their female genitor and a Y chromosome from their male genitor. Just like in humans! In fact, just like all mammals. This is the system Nature uses to produce scores of male and female animals. Now give this a thought: if some fruit flies are XX and others are XY, do the former not have more of something? And the latter something else altogether? For the XY individuals, the answer is yes. That is what makes them male. For the XX individuals, however, the answer is no. Though they may carry an extra X chromosome, in Drosophila, researchers have discovered a protein whose role is to prevent any kind of genetic imbalance with regards, precisely, to X-linked genes. Its name? MSL2.
