The "thread of life", is deoxyribonucleic acid, otherwise known as DNA. It is the spiral shaped molecule found in the nucleus of cells. Scientists have known since 1952 that DNA is the basic substance of heredity. This was hypothesized, and later confirmed by James D. Watson and Francis Crick. They also know that it acts like a biological computer program over 3 billion bits long that "spells" out instructions for making the basic building blocks of life.
DNA carries the bodies genetic code, controls the development of an embryo, is capable of duplicating itself, and is able to repair damage to itself. DNA can be manipulated to change all kinds of things.
All DNA molecules consist of a linked series of unites called nucleotides. Each DNA nucleotide is composed of 3 subunits: a 5 carbon sugar called deoxyribose, a phosphate group that is joined to one end of the sugar molecule, and one of several different nitrogenous bases linked to the opposite end of the deoxyribose. There are 4 nitrogen bases called adenine, guanine, thymine, and cytosine. In DNA adenine pairs with thymine and guanine with cytosine. Medicine's ability to diagnose continues to exceed its ability to treat or cure. For example, Huntington's Chorea is an inherited disease that develops between the ages of 30 and 45, can be diagnosed before any symptoms appear. This can be hard for both the individuals with the disease and their family.
There is a 3 billion dollar project underway right now called the Human Genome Project, a 15 year program to make a detailed map of every single gene in human DNA. With automated cloning equipment to steer scientists through the DNA, scientists are finding human genes at the rate of more than one a day. This may not sound like very much but as technology increases the rate at finding them will increase. Since January 1993 to January 1994 scientists have located the genes for Huntington's disease, Lou Gehrig's disease, and the "bubble-boy" disease.