What happens in Meiosis if the chromosomal number is off by one number?

Answer 1

Depending on the chromosome in question, various diseases will occur, or the zygote may not form.
Calico cats are all victims of having 47 chromosomes (47xxy). -You can't get the colour variation, otherwise (My favorite example). ...This is Kleinfelter's Syndroms in humans.
There's also Turner Syndrome and Down Syndrome.

Try looking up "Chromosomal aberation" online.

Answer 2

down syndrome