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					                              Pair-Rule Gene

Pair-rule    gene is    a   type  of gene involved    in   the development of
the segmented embryos of insects. Pair-rule genes are defined by the effect of
a mutation in that gene, which causes the loss of the normal developmental
pattern in alternating segments.


Pair-rule genes were first described by Christiane Nüsslein-Volhard and Eric
Wieschaus in 1980. They used a genetic screen to identify genes required for
embryonic development in the fruit fly Drosophila melanogaster. In normal
unmutated Drosophila, each segment produces bristles called denticles in a band
arranged on the side of the segment closer to the head. They found five genes –
 Even-skipped, Hairy, Odd-skipped, Paired and Runt – where mutations caused
the deletion of a particular region of every alternate segment. Once the pair-rule
genes had been identified at the molecular level it was found that each gene
is expressed in alternate Parasegments – regions in the embryo that are closely
related to segments, but are slightly out of register. Each parasegment includes
the posterior part of one segment, and an anterior part of the next segment. The
bands of expression of the pair-rule genes correspond to the regions missing in
the mutant. The expression of the pair-rule genes in bands is dependent on direct
regulation by the gap genes.

				
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posted:3/22/2011
language:English
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