When the full map of the human genome is known … we shall have passed through a phase of human civilization as significant as, if not more significant than, that which distinguished the age of Galileo from that of Copernicus, or that of Einstein from that of Newton.… We have crossed a boundary of unprecedented importance.… There is no going back.… We are walking hopefully into the scientific foothills of a gigantic mountain range.
—Ian Lloyd, 1990
In 1953 James Watson and Francis Crick described the double helical structure of deoxyribonucleic acid (DNA). Their molecular DNA structure was published in Nature on April 25, 1953, in an article that was little more than one page. Their article ushered in a new age of discovery in genetics and laid the foundation for the sequencing of the human genome.
The word "genome" was derived from two words—gene and chromosome. Today, "genome" is widely understood to be the entire complement of genetic material in the cell of an organism. A genome is composed of a series of four nitrogenous DNA bases: adenine (A), guanine (G), thymine (T), or cytosine (C). In each organism these bases are arranged in a specific order, or sequence, and this order constitutes the genetic code of the organism. In humans the genome is composed of approximately three billion bases. In 2001 a first draft sequence of the entire human genome was completed and made available to the public for study and research. The National Human Genome Research Institute (NHGRI), which is one of the National Institutes of Health (NIH), Human Genome Project completed the full human genome sequence in April 2003.
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