It is also easy to see how a mutation could lead to the loss of a binding site in a regulatory region. A new binding site (lock) has evolved to match a master protein (key) that was already around.

If this new pattern proved advantageous for the organism, further mutations in the regulatory region might then be selected for to improve the match, creating an even better binding site. This sort of mutation might start to couple the interpreting gene to a different master protein, modifying the gene's pattern of expression. In a regulatory region a few thousand bases long, it is not too improbable that a chance mutation altering one or two bases in the DNA could create a new binding site for a master protein, or at least something that came reasonably close to a new binding site. Binding sites are quite short stretches of DNA, typically six to ten bases long. For this reason, evolutionary changes are often likely to involve mutations in the sites within regulatory regions, rather than alterations in the regions coding for the master proteins themselves.ДЄn example of a change in a regulatory region might be the creation of a new binding site. In contrast, by changing a binding site in the regulatory region of a gene, only the expression of that gene will be directly affected. Because a typical master protein might bind to as many as one hundred different interpreting genes, an enormous constraint is imposed on the extent to which the shape of this master protein can be modified during evolution: any significant change may jeopardise the expression of all one hundred genes it normally binds to, most likely with disastrous consequences for the development and survival of the organism.

Rooms, much of biological evolution has involved changes in the binding sites within regulatory regions (locks) rather than in the master proteins themselves (keys).

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