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This afternoon, Ira Flatow will be talking with medical educator Howard Markel about the word genome on and I can't wait to tune in! The word has a pretty fascinating 80-year history and we use it all the time in the stories we write and blog entries we post. As such, we've added "genome" as a term to our glossary.

A genome is the full set of instructions needed to make every cell, tissue, and organ in your body. Almost every one of your cells contains a complete copy of these instructions, written in the four-letter language of DNA (A, C, T, and G). The human genome contains 3 billion of these "letters" or bases. This means that if your genome were written out on sheets of paper and stacked as books, the tower of tomes would be almost as high as the Washington Monument!

If you think of the human genome as an encyclopedia, the information it contains is divided into 23 volumes, called chromosomes. Each chromosome contains genes - "sentences" of genetic instructions that tell the cell how to make proteins. We know the human genome contains about 20,500 of these genes, but the meaning of much of the remaining text within it is a mystery.

You can find the full entry on "genome" here.