Every cell in every living thing (or organism) has DNA, a molecule that contains all the information about that organism. Building on research by others before them, the structure of DNA was discovered in 1953 by the British scientist Francis Crick and the American scientist James Watson. James Watson was a World Almanac reader as a kid.
Lengths of connected DNA molecules, called genes, are like tiny pieces of a secret code. They determine what each organism is like in great detail. Almost all the DNA and genes come packaged in rod-like structures called chromosomes--humans have 46. There are 22 almost identical pairs, plus the X and Y chromosomes, which determine if a human is male (one X chromosome and one Y chromosome) or female (two X chromosomes).
Genes are passed on from parents to children, and no two organisms (except clones and identical twins) have the same DNA. Many things--the color of our eyes or hair, whether we're tall or short, our chances of getting certain diseases--depend on the genes we get from our parents
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