In the orchestra of cell division, every chromosome has to sound at exactly the right moment. But with age the conductor starts making mistakes: now the violin misses its cue, now the cello plays twice. Cells appear in the blood where one chromosome is missing or, conversely, there are two instead of one. Such glitches used to be considered random, like forgotten notes. A new study of nearly a million people showed that each of us has our own notes that drop out more often.
Heritability turned out to be strong. In identical twins, the loss of the X chromosome in women matched 60% of the time, and the loss of Y in men 62%. That means the tendency toward such errors is written into the genes rather than coming from outside. For X loss, they found 245 DNA regions; for Y loss, a full 828. In ten other chromosomes, they discovered 173 new regions. Each chromosome is like a separate instrument in the orchestra: each has its own part, its own weak spots.
They checked whether these losses affect health. It turned out they almost don't: only a weak link to prostate cancer. This changes earlier ideas that losing the Y chromosome hits the body hard. The conductor errs, but the orchestra keeps playing.
Now it's clear: each chromosome has its own set of genetic variants that decide how often it will drop out of cell division. It's as if every musician in the orchestra had their own sheet music with mistakes. Which notes will go missing depends on the score inherited from your parents.
One of the structural variants discovered, a hybrid chromosome 13/22, arose from a rare recombination between centromeres and occurs in roughly one in 30 people of southern European ancestry.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.