Intelligent Design, the best explanation of Origins

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Intelligent Design, the best explanation of Origins » Molecular biology of the cell » Development biology » Segmentation Genes

Segmentation Genes

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1 Segmentation Genes on Thu Dec 06, 2018 9:07 am

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Segmentation Genes

Cell fate commitment in Drosophila appears to have two steps: specification and determination. Early in fly development, the fate of a cell depends on cues provided by protein gradients. This specification of cell fate is flexible and can still be altered in response to signals from other cells. Eventually, however, the cells undergo a transition from this loose type of commitment to an irreversible determination. At this point, the fate of a cell becomes cell-intrinsic. The transition from specification to determination in Drosophila is mediated by segmentation genes that divide the early embryo into a repeating series of segmental primordia along the anterior-posterior axis. Segmentation genes were originally defined by zygotic mutations that disrupted the body plan, and these genes were divided into three groups based on their mutant phenotypes



• Gap mutants lack large regions of the body (several contiguous segments; Figure A).
• Pair-rule mutants lack portions of every other segment (Figure B).
• Segment polarity mutants show defects (deletions, duplications, polarity reversals) in every segment (Figure C)


Three types of segmentation gene mutations. 
The left side shows the early-cleavage embryo (yellow), with the region where the particular gene is normally transcribed in wild-type embryos shown in blue. These areas are deleted as the mutants develop into late-stage embryos.

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