How does the length of DNA directly relate to its ability to code for a complex organism such as a human being?

All living organisms are composed of cells, each no wider than a human hair. Each of our cells contains the same complement of DNA constituting the human genome (Figure 1-1.) The DNA sequence of every person's genome is the blueprint for his or her development from a single cell to a complex, integrated organism that is composed of more than 1013 (10 million million) cells. Encoded in the DNA sequence are fundamental determinants of those mental capacities—learning, language, memory—essential to human culture. Encoded there as well are the mutations and variations that cause or increase susceptibility to many diseases responsible for much human suffering. Unprecedented advances in molecular and cellular biology, in biochemistry, in genetics, and in structural biology—occurring at an accelerating rate over the past decade—define this as a unique and opportune moment in our history: For the first time we can envision obtaining easy access to the complete sequence of the 3 billion nucleotides in human DNA and deciphering much of the information contained therein. Converging developments in recombinant DNA technology and genetics make obtaining a complete ordered DNA clone collection indexed to the human genetic linkage map a realistic immediate goal. Even determination of the complete nucleotide sequence is attainable, although ambitious. The DNA in the human genome is remarkably stable, as it must be to provide a reliable blueprint for building a new organism. For this reason, obtaining complete genetic linkage and physical maps and deciphering the sequence will provide a permanent base of knowledge concerning all human beings—a base whose utility for all activities of biology and medicine will increase with future analysis, research, and experimentation.

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