Evolution Under Pressure: How We Change Nature and How Nature Changes Us

Evolution Under Pressure: How We Change Nature and How Nature Changes Us — page 9
Where do these random changes happen In the genes bits of instruction inside each cell that determine how a living crea ture will develop function and reproduce These instructions are made of DNA deoxyribonucleic acid Just like English is written using a code of twenty-six letters genes are written with four letters or bases of DNA When a living creature reproduces it passes on the genes in its instruction man ual to the next generation by copying and packaging all those DNA bases into the nucleus of a new cell This is how the next generation begins with a single cell and a genetic instruction manual on how it can grow up to be just like its parent by making more and more cells But even the offspring of single-celled organisms can turn out different than their parent Why Mistakes are sometimes made in the copying of DNA Like a spell ing mistake changing one of the letters in a gene’s code often called a mutation can change how the instructions are read Gene Mutations 6 EVOLUTION UNDER PRESSURE