The entire system needed to have a sense of smell. This system involves at least 1,000 genes for the olfactory receptors. These genes are members of a large family of genes that encode signaling proteins required for the detection and discrimination of odors. Many of these olfactory genes are arranged in large clusters on chromosomes 6, 11, and 17, as well as distributed on other chromosomes. The mouse has more genes than do humans relating to reproduction, immunity and olfaction, suggesting that these physiological systems have been the focus of extensive innovation in rodents. It seems that sex, infection, and smell have been most on the mouse's evolutionary mind [MedTerms: http://www.medterms.com/script/main/art.asp?articlekey=39211].
Hierarchy: 2
Parent: peripheral nervous system
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