Editing Cistron (section)

{{Short description|Region of DNA equaling a gene as defined by complementation test}}
{{More citations needed|date=February 2021}}

A '''cistron''' is a region of [[DNA]] that is conceptually equivalent to some definitions of a [[gene]], such that the terms are synonymous from certain viewpoints,<ref>{{cite book | last = Lewin | first = Benjamin | name-list-style = vanc | authorlink = Benjamin Lewin | title = Genes VII | year = 2000 | publisher = Oxford University Press and Cell Press | location = New York | isbn = 0-19-879276-X | page = [https://archive.org/details/genesvii00lewi/page/955 955] | url-access = registration | url = https://archive.org/details/genesvii00lewi/page/955 }}</ref> especially with regard to [[gene#Definitions|the molecular gene as contrasted with the Mendelian gene]]. The question of which scope of a subset of DNA (that is, how large a segment of DNA) constitutes a [[unit of selection]] is the question that governs whether cistrons are the same thing as genes<!--as further explained in the article body below; lede summarizes body-->. The word ''cistron'' is used to emphasize that molecular genes exhibit a specific behavior in a [[complementation test]] (cis-trans test); distinct positions (or [[locus (genetics)|loci]]) within a [[genome]] are '''cistronic'''.