You may not believe this, but I have 24 pairs of chromosomes. My mum was 41 when she had me, I am now 23, and being as she was quite old back then to have a child they performed quite a lot of extra tests on her to make sure we were both ok. When I was born, the doctors wanted to take the after birth to perform tests to see if it were true, but a misunderstanding meant that it was thrown away and she wouldnt allow the doctors to do tests on me, so they never got to the bottom of it. So obviously it could be a mistake, but as far as I know, there is no difference, I'm exactly the same as everyone else! Although, if it is true, my understanding of genetics is that if I have 24 pairs of chromosomes then so do my two brothers...which leads me to my brothers 4yr old son who has 6 toes on one foot, that could be the extra pair at work!