Introduction to Genetic Analysis 446

Introduction to Genetic Analysis 446 - 44200_13_p423-450...

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evolved are not known. However, it is reasonable to assume that a Drosophila ancestor used telomerase like other organisms but that this mechanism was lost in favor of retrotransposition of HeT-A and TART elements. 13.5 Host regulation of transposable elements Reversible changes in Ac activity While Barbara McClintock was characterizing the trans- posable elements of maize, she discovered a very un- usual phenomenon. Some autonomous elements, such as Ac , would turn off for part of the plant life cycle or even for several generations and then turn back on again. While off, Ac could not itself move or promote the movement of Ds elements in the genome. She called this reversible change in the activity of Ac change in phase. To better understand what is meant by change in phase, let’s see how the phenomenon appears in the pig- ment of corn kernels. Recall from Figure 13-4 that a strain with Ds inserted into the C gene [the c-m(Ds) al- lele] will have spotted kernels if Ac is in the genome. However, in some of these strains, the kernels are not
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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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