Evolution occurs through genome variation followed by selection. Because DNA sequence context affects the activity of enzymes that copy, move and repair DNA, there are intrinsic variations in the probability of genetic variation along a genome. These intrinsic variations can be affected by selective pressure. Codon changes that do not alter the encoded amino acids may still have effects on the local rate of sequence change. Large gene families could encode a successful genetic framework by which to evolve new, functional members. The speed of adaptation to environmental challenges may be improved when the distinct mechanisms of genetic change come under regulatory control. Natural selection operates on mechanisms that generate and modulate diversity as it does on all biological functions. Copyright 2000 John Wiley Sons, Inc.
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