Editing Evolutionary developmental biology (section)

===The lac operon===
{{Main|Lac operon}}

[[File:Lac Operon.svg|thumb|275px|The [[lac operon]]. Top: repressed. Bottom: active. (1) [[RNA Polymerase]], (2) [[lac repressor|Repressor]], (3) [[Promoter (genetics)|Promoter]], (4) Operator, (5) [[Lactose]], (6–8) [[structural gene|protein-encoding genes]], controlled by the switch, that cause lactose to be digested.]]

In 1961, [[Jacques Monod]], [[Jean-Pierre Changeux]] and [[François Jacob]] discovered the [[lac operon]] in the [[bacterium]] ''[[Escherichia coli]]''. It was a cluster of [[gene]]s, arranged in a feedback [[control loop]] so that its products would only be made when "switched on" by an environmental stimulus. One of these products was [[β-galactosidase|an enzyme that splits a sugar]], lactose; and [[lactose]] itself was the stimulus that switched the genes on. This was a revelation, as it showed for the first time that genes, even in organisms as small as a bacterium, are subject to precise control. The implication was that many other genes were also elaborately regulated.<ref>{{Cite journal |last=Monod |first=Jacques |author-link=Jacques Monod |last2=Changeux |first2=J.P. |last3=Jacob |first3=François |author-link3=François Jacob |year=1963 |title=Allosteric proteins and cellular control systems |journal=Journal of Molecular Biology |volume=6 |issue=4 |pages=306–329 |doi=10.1016/S0022-2836(63)80091-1 |pmid=13936070}}</ref>