How can you lose a chromosome?
Telomeres.
Each time a cell divides, the telomeres become slightly shorter.
Eventually, they become so short that the cell can no longer divide successfully, and the cell dies.
The above is my guess of what the author is referring to.
Must be like loose change - falls out of your pocket -
if you're lucky you find it under the couch cushions...
/s
How can you lose a chromosome?
About as easy as ‘losing’ my car keys or cell phone?