Have you done DNA testing? I decided to bite the bullet and send in some of my white blood cells to see what I might learn about my biological history. Before I go into that, a bit of review. As you probably already know from high school biology, your complete set of genetic information is encoded within 23 pairs of chromosomes in the nucleus of your cells—the 23rd pair typically being a XX or a XY pattern. (Not all cells have a nucleus, by the way. Red-blood cells, for instance, do not.) A chromosome is a single piece of coiled DNA or deoxyribonucleic acid, a biomolecule that holds the blueprint for how living organisms are built. 99% of all DNA in your body is found in your chromosomes. Segments of DNA called genes are passed down from parents to child and confer traits to the offspring. Humans have 25,000-30,000 genes, usually in pairs (one from each parent).