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Script: The zygote's 46 chromosomes represent the unique first edition of a new individual's complete genetic blueprint. This master plan resides in tightly coiled molecules called DNA. They contain the instructions for the development of the entire body. DNA molecules resemble a twisted ladder known as a double helix. The rungs of the ladder are made up of paired molecules, or bases, called guanine, cytosine, adenine, and thymine. Guanine pairs only with cytosine, and adenine with thymine. | ||
All ages referenced to fertilization, not last menstrual period. |