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.
Most mammals have only one pair of sex chromosomes in each cell. Males have one Y chromosome and one X chromosome, while females have two X chromosomes. In mammals, the Y chromosome contains a gene, SRY, which triggers embryonic development as a male. The Y chromosomes of humans and other mammals also contain other genes needed for normal sperm production.
A normal human karyotype, for example, includes 46 chromosomes or 23 pairs of chromosomes. Of these 46 chromosomes, both the male and the female each possess 22 pairs of autosomes, or non-sex chromosomes, and one pair of sex chromosomes.For the male, the sex chromosomes are XY.he term karyotype refers to the basic map, or picture, of the number,type, and structure of the chromosomes of a cell. The karyotype is created through a process in which a cell s mitotic division is halted or trapped during metaphase and held suspended by chemicals.