DNA Testing Introduction
In our quest to understand Genetic Genealogy (DNA testing), we must have knowledge of the basics of the Human DNA structure. Deoxyribonucleic acid (DNA) is the chemical compound that contains the instructions needed to develop and direct the activities of nearly all living organisms. DNA molecules are made of two twisting, paired strands of Polynucleotides often referred to as a double helix. DNA represents the building codes for life and the instructions to maintain it.
Each DNA strand is made of four chemical units, called nucleotide bases, which comprise the genetic "alphabet". The bases in DNA are adenine(A), thymine(T), guanine(G),and cytosine (C). These are the “rungs” of the ladder in the DNA sequence. Bases on opposite strands pair specifically: an A always pairs with a T; a C always pairs with a G. The order of the As, Ts, Cs, and Gs in DNA determines the meaning of the information encoded in that part of the DNA molecule just as the order of letters determines the meaning of a word. This sequence is determined by DNA testing. The results of DNA testing will provide an understanding of your personal DNA genealogical identity.
An organism's complete set of DNA instructions is called its genome. Every single cell in the body contains a complete copy of the approximately 3 billion DNA base pairs, or letters, that make up the human genome. The entire human genome has been sequenced through DNA testing.
With its four-letter language, DNA contains the information needed to build the entire human body. A gene traditionally refers to the unit of DNA that carries the instructions for making a specific protein or set of proteins. Each of the estimated 20,000 to 25,000 genes in the human genome codes for an average of three proteins.
Sequencing simply means determining the exact order of the bases in a strand of DNA by utilizing DNA testing. Because DNA bases exist as pairs, and the identity of one of the DNA bases in the pair determines the other member of the pair, researchers do not have to report both DNA bases of the pair.
In one method of DNA testing, called the chain termination method , a DNA strand can be treated with a variety of nucleotides , a set of enzymes, and a specific primer to generate a collection of smaller DNA fragments. Each of the fragments differs in length by one base and is marked with a fluorescent tag that identifies the last base of the fragment. The fragments are then separated according to size and passed by a detector that reads the fluorescent tag. Then, a computer reconstructs the entire sequence of the long DNA strand by identifying the base at each position from the size of each fragment and the particular fluorescent signal at its end.