Although the largest differences in the amount of DNA between different species are the result non-coding DNA (see the preceding section), differences also occur in the number of genes between different organisms.
Think back to the branching tree of life (refer to Chapter 9) and the evolution of more complex organisms such as humans from less-complex organisms. You can appreciate why the number of genes has increased. In this section, I explain how the number of genes an organism has can change. New genes can appear in a variety of ways.
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