9781422281352

anything to do with genetics seems to cause all kinds of argu- ments and protests.” DNA and Genes Imagine that you have to build a complex machine from thou- sands of parts. To fit them together, you need a set of instruc- tions. A living organism is far more complicated than any machine. It has billions of parts that work together. It also needs a set of instructions, so it can grow, develop, and survive. The instructions for a machine are usually written 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 sec- tions of that code sequence. A machine’s instructions are big enough for us to see, but genes are so 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 a 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

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Genetic Engineering