HOMOLOGIES (CONTINUED)

Organisms have genes that perform two separate functions.  One set of genes controls the existence (or lack thereof) of a particular feature.  These are called structural genes.  The other set controls if, when, and for how long the structural genes are allowed to function.  These are called regulatory genes.  the diagram below shows the effects of different regulatory gene control on the development of two vertebrate limbs: a human arm and a bat wing.  Examine each corresponding bone and compare their relative sizes after growth.

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