There are almost as many different types of four-wheel-drive systems as there are four-wheel-drive vehicles. It seems that every manufacturer has several different schemes for providing power to all of the wheels.
Human Male Chromosomes. In the normal karyotype of male chromosomes, 23 pairs of very long DNA molecules and their associated proteins carry the hereditary information of a man.
A karyotype is an organized profile of a person's chromosomes. Two chromosomes specify gender  XX for female and XY for male. The rest are arranged in pairs, numbered 1 through 22, from largest to smallest. This arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic disorder.