Is the number of human chromosomes fixed, or could it change?

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Science has long known that humans have 46 chromosomes in total (22 pairs plus X & Y). But is that number fixed or is it possible that it could change?

These web pages explore one of the ways that individuals can end up with different chromosome numbers, how those changes can be passed on to their offspring and what would be needed for such a change to spread through the human species.

This web site is divided into the following sections:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 XY

(Human chromosome images from Wikipedia)