DNA Basics

What is DNA?
Deoxyribonucleic acid is a molecule found in nearly all human cells. DNA contains the information for the development and function of all living organisms. A human DNA molecule is a double helix, shaped like a twisted ladder. The human genome is the complete set of human genetic information found within 23 pairs of chromosomes for each person. Half of the chromosomes come from the father and half from the mother. These 23 chromosomes reside within the nucleus of our cells and some DNA is also found within the mitochondria.

Why use it in genealogical research?

Companies that do DNA testing
See the Wiki article, Hiring a DNA Testing Company.