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Gap gene
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<p>A gap gene is a type of <a href="/facts/Gene/e1swwPY6">gene</a> involved in the <a href="/facts/Development_(biology)/ckqaQlL7">development</a> of the <a href="/facts/Segmentation_(biology)/S4Cw0UcN">segmented</a> <a href="/facts/Embryos/9QHnLVLN">embryos</a> of some <a href="/facts/Arthropods/JKJLTFzp">arthropods</a>. Gap genes are defined by the effect of a <a href="/facts/Mutation/Ee4NnWbY">mutation</a> in that gene, which causes the loss of contiguous body segments, resembling a gap in the normal body plan. Each gap gene, therefore, is necessary for the development of a section of the organism. </p> <p>Gap genes were first described by <a href="/facts/Christiane_N%25C3%25BCsslein-Volhard/Nq8WBuNk">Christiane Nüsslein-Volhard</a> and <a href="/facts/Eric_Wieschaus/Jg6aydc2">Eric Wieschaus</a> in 1980. They used a <a href="/facts/Genetic_screen/l4XLmjaj">genetic screen</a> to identify genes required for embryonic development in the fruit fly <i><a href="/facts/Drosophila_melanogaster/KtnHVCcB">Drosophila melanogaster</a></i>. They found three genes – <i>knirps, <a href="/facts/Kr%25C3%25BCppel/8KP33WSJ">Krüppel</a> and <a href="/facts/Hunchback_(gene)/6trwGkSe">hunchback</a></i> – where mutations caused deletion of particular stretches of segments. Later work identified more gap genes in the <i>Drosophila</i> early embryo – <i>giant</i>, <i>huckebein</i> and <i>tailless</i>. Further gap genes including <a href="/facts/Orthodenticle/P1Gvd2uJ">orthodenticle</a> and buttonhead are required for the development of the <i>Drosophila</i> head. </p><p>Once the gap genes had been identified at the molecular level it was found that each gap gene is <a href="/facts/Gene_expression/alCPohLR">expressed</a> in a band in the early embryo generally correlated with the region that is absent in the mutant. In <i>Drosophila</i> the gap genes encode <a href="/facts/Transcription_factors/wro0DPHe">transcription factors</a>, and they directly control the expression of another set of genes involved in segmentation, the <a href="/facts/Pair-rule_gene/puIQ44PI">pair-rule genes</a>. The gap genes themselves are expressed under the control of <a href="/facts/Maternal_effect/551Xye08">maternal effect</a> genes such as <i><a href="/facts/Bicoid/u1C4oYRg">bicoid</a></i> and <i><a href="/facts/Drosophila_embryogenesis/CRro4E9n">nanos</a></i>, and regulate each other to achieve their precise expression patterns. </p>