Introduction to Genetic Analysis 598

Introduction to Genetic Analysis 598 - accordingly to...

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Unformatted text preview: accordingly to execute the increasingly finer subdivisions of the embryo, establishing both segment number and segment identity (Figure 18-26). 18.6 Refining the pattern The principles delineated in the preceding sections lay out initial fates, but additional mechanisms must be in place to ensure that all aspects of patterning are elaborated. Some of these mechanisms are considered in this section. Memory systems for remembering cell fate Patterning decisions frequently need to be maintained in a cell lineage for the lifetime of the organism. This re- quirement is certainly true of the segment-polarity and homeotic gene expression patterns that are set up by the AP patterning system. The key is that patterning deci- sions are maintained through positive-feedback loops. Such positive-feedback loops may operate entirely within a cell. In several tissues, positive-feedback loops are established in which the homeodomain protein that is expressed binds to enhancer elements in its own gene, ensuring that more of that homeodomain protein...
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

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