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Pair-rule genes in Drosophila development

  1. Nov 8, 2003 #1
    Hey guys,

    So I have an exam tomorrow afternoon on developmental bio (ugh ), and i have been going over my notes and have run into something i'm struggling to understand.

    The topic is Drosophila development, and the brick wall I have run into involves the way in which pair-rule genes work their magic.

    I can understand the way in which Gap genes work, however when it comes to pair-rule genes it goes way over my head. The notes I have explaining them are quite bad, so I was wondering if you guys have an explanation that would be much more useful.

    Cheers guys :smile:
  2. jcsd
  3. Nov 9, 2003 #2


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    The products of the egg-polarity genes provide the global positional signals in the early embryo. These cause particular gap genes to be expressed in particular regions. The products of the gap genes then provide a second tier of positional signals that act more locally to regulate the finer details of patterning through the expression of yet other genes, including the pair-rule genes.

    Does that answer your question?

    Gap genes (at least 6): the products mark out coarse subdivions of the embryo. Mutations in a gap gene eliminate one ro more groups of adjacent segments, and mutations in different gap genes cause different but partially overlapping defects.

    Pair-rule genes (8): mutations in these cause a series of deletions affecting alternate segments, leaving the embryo with only half as many segments as usual. While all the pair-rule mutants display this two-segment periodicity, they differ in the precise positioning of the deletions relative to the segmental or parasegmental borders.

    Segment polarity genes (10): mutations in these genes produce larvae with a normal number of segments but with a part of each segment deleted and replace by a mirror-image duplicate of all or part of the rest of the segment.

    Then the homeotic selector genes serve to define and preseve the differences between one segment and the next.

    Source: Alberts et al, Molecular Biology of The Cell
  4. Nov 9, 2003 #3
    That helped a bit. Thanks monique :smile:
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