9781422280751

There’s nearly five feet (1.5 meters) of DNA in each of your cells—if you laid all the DNA in your body end to end it would reach to the sun (93 million miles) and back about 40 times! SIDEBAR

any machine. It has billions of parts that work together. Yet, it also needs a set of instructions, so it can grow, develop, and survive. The instructions for a machine are usually wrien on paper. Those for a living thing are in the form of a molecule called deoxyribonucleic acid ( DNA ), a sequence of codes that exists in every cell. In 1953, James Watson and Francis Crick discovered that DNA looks like a long ladder twisted into the shape of a corkscrew called a double-helix. The double-helix shape plays an important role in the way a gene is copied so that its product can be made.

If DNA is the “instruction book,” genes are like individual pages of the book that explain how to make specific parts of the machine: in the DNA sequence of codes, genes make up sections of that code sequence. A machine’s instructions are big enough for us to see, but genes are so

Gregor Mendel is considered the father of genetics. He was the first to show how characteristics could be passed on from one generation to another.

tiny they can only be seen by using special microscopes. All the genes for a living thing, from a daisy or worm to a tree or whale, are in pieces of DNA that could fit onto the period at the end of this sentence. HOW GENES WORK All living things are made of cells, which are like building blocks. Cells are so small that about 10,000 would fit inside this “o.” There are 37.2 trillion cells in a human body, but a gene section of DNA is even smaller than a cell. To a gene, a cell is like a gigantic “living factory.”

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