Among plants and animals, species tend to increase their number of chromosomes when they want greater diversity and adaptability. They tend to decrease their number of chromosomes when they are trying to save energy.
The human species seems to be trying to decrease our number of chromosomes. This seems to be why we have 46 pairs, but other primates: gorillas, chimpanzees and orangutans have 48 pairs.
In any event, this may explain the ‘Y’ chromosome of males. Originally, it was likely an ‘X’ chromosome, but one of its ‘arms’ or ‘legs’ was broken off and no longer copied.
Eventually, the ‘Y’ chromosome is expected to fail. But a replacement is waiting in the wings, as it were. The ‘X’ sex chromosome, the female chromosome, seems to be weakening. A common cause of birth defects today is called “Fragile X Syndrome”, in which one of the ‘arms’ or ‘legs’ of the ‘X’ sex chromosome is damaged or even broken.
So the ‘Y’ chromosome fails, and is replaced by a new ‘Y’ chromosome, and another ‘X’ chromosome replaces it as a sex chromosome.
Keep on smokin that stuff!
Fragile X Syndrome has nothing to do with the X chromosome breaking. In the mutation, the X has a large number of serial tandem repeats. It’s named for the appearance this gives it on staining, with a separated piece due to the unmarked section.