For a long time, so-called satellite DNA was considered largely worthless. Now, ETH Zurich researchers have shown in fruit flies that these repetitive sections of genetic material act as a kind of barcode, enabling the correct chromosomes to recognize one another.

The body cells of humans and animals contain a double set of chromosomes. One-half of the genetic material comes from the mother; the other stems from the father.

During the formation of sperm or egg cells, this double set of chromosomes must be halved to form a single set. This takes place during what is known as meiosis. In this process, a cell with a double set of chromosomes gives rise to daughter cells with a single set of chromosomes. This halving is necessary because, during fertilization, two germ cells—and thus their genetic material—fuse together.

Afterwards, there is once again a double set of chromosomes. If this did not happen, the number of chromosomes would double from one generation to the next as the germ cells fuse.

To ensure that chromosomes can be distributed evenly during meiosis, the maternal and paternal versions of the same chromosome must locate one another within a cell and temporarily pair up. This is no easy task amid the vast jumble of the cell nucleus. Mismatches must be avoided at all costs during the pairing phase to prevent chromosomes from being distributed incorrectly.

But how do the matching chromosome pairs actually find each other? ETH researchers led by Madhav Jagannathan, a professor at the Department of Biochemistry, and his Ph.D. student Lena Skrutl have now investigated—using the example of egg cell formation in female fruit flies (Drosophila)—how this "matchmaking" process takes place in the cell nucleus and have made a surprising discovery.