How many pairs of chromosomes does an person with autism have?
Autism is not caused by an extra chromosome. You may be thinking of Down syndrome, which is caused by an extra 21st chromosome; the person does not have 24 pairs of chromosomes, but rather 47 chromosomes, total. The possession of an extra chromosome in general is called trisomy, and it is caused by nondisjunction, the failure of chromosomes to separate properly during cell division in the production of gametes (sperm and eggs). The causes of autism are less well understood. It is thought to be heritable, with multiple genetic and epigenetic models proposed, but not chromosomal in nature. There may also be chemical factors. Doom is a pretty bad movie.