Primer - Primer Because the arguments advanced in Explore...

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Primer Because the arguments advanced in Explore Evolution require readers to have a level of knowledge beyond that offered in the book or in standard high school or college introductory biology texts, this primer on developmental biology and evolutionary developmental biology may be useful for some readers. The genetic regulation of segmentation: On the left, patterns of gene expression in a developing Drosophila embryo. On the right, a diagram of the regulatory interactions between the genes which produce this patterning. Arrows indicate positive regulatory interactions, a line ending in a flat line indicates negative feedback. Sean B. Carroll, Jennifer K. Grenier, and Scott D. Weatherbee (2001) From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design , Blackwell Publishing:Cambridge, MA, p. 59, fig. 3.5 A good resource for the basic background necessary is From DNA to Diversity by Sean Carroll, or his book Endless Forms Most Beautiful . Carroll describes developmental biology in terms of "tool kits" of genes. A group of genes which interact and regulate one another's expression would form such a tool kit, and such kits can operate as somewhat independent modules. "Modularity," explains Rasmus Winther, "is central to the current evolutionary developmental biology synthesis" (R. G. Winther, 2001, "Varieties of Modules: Kinds, Levels, Origins, and Behaviors," J. Exper. Zool. (Mol. Dev. Evol.) 291:116–129). How those modules interact is controlled by other toolkits, producing a hierarchy of kits. For example, in Drosophila , five hierarchal tiers of regulation (maternal effect, gap, pair-rule, segment polarity, and homeotic) are involved in organizing the body pattern along the axis from head to tail of the developing embryo. Each segment of the body is produced through interactions between gene products translated from mRNAs deposited in the egg by the mother, transcriptional activation of genes in the egg by such maternal activators, and combinatorial action of segmentation gene products (tool kits) to refine the expression patterns of many zygotic genes.
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Explore Evolution skips any presentation of this regulatory network of tool kits and invites the students to compare the regulation of body segmentation in fruit flies and wasps, declaring: "The body segments of some wasps arise from developmental pathways that are entirely different from those of fruit flies, and even from other wasps" ( EE , p. 44). The student has no way to evaluate this claim, nor to judge its significance, because high school biology texts rarely cover developmental biology, and EE certainly doesn't offer that background. In the diagram of Drosophila segmentation shown above, the seven stripes that make up the expression patterns of the primary pair-rule genes hairy and even-skipped are controlled independently. That is, different regulatory elements control the expression of different stripes. Wasp vs. fly development:
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This note was uploaded on 11/08/2011 for the course BIOLOGY BSC1086L taught by Professor Leostouder during the Fall '10 term at Broward College.

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Primer - Primer Because the arguments advanced in Explore...

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