The human body is made up of about 100 trillion cells.
Most cells have a nucleus.
Inside each nucleus are 46 packets called chromosomes. It is estimated that within the DNA there are up to 100,000 genes, positioned something like towns and cities along a major highway. The DNA of animals and humans is remarkably similar. For example, the genetic makeup of chimpanzees differs from that of humans by only 1 percent. Still, that gap is ten times wider than the differences between the DNA of any two humans.