National Geographic News, Reporting Your World Daily

Sunday, September 7, 2008

Photo: Coming Soon: Your Personal DNA Map?


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The chemical DNA (deoxyribonucleic acid) includes the instructions for all cells, the basic working units of every living thing. Twisted double strands of DNA are joined together by linked pairs of bases (A, T, C, and G) like the rungs of a ladder.

Specific combinations of bases are called genes. Their arrangements are codes for making distinct types of proteins. Joined together in long DNA strands, these genes form x- and y-shaped chromosomes, of which nearly all humans have 24.

A complete set of DNA for a species is called a genome.

Illustration courtesy U.S. Department of Energy