FIGURE 24.16 Principle of the Nanopore Detector

(A) Nanopores are small openings in a membrane that only allow one molecule through at a time. The nanopore membrane separates two compartments of different charge. (B) Since there is a charge separation between compartments, negatively charged molecules like DNA can pass through the pore in an extended conformation. (C) While the DNA is passing through the pore, a detector measures how much the current, due to normal ion flow, is reduced. Since each base alters the current by different amounts, the detector can determine the sequence as the DNA passes through the pore.

by PCR. An EST represents only a small section of a gene, thus it is possible to have several ESTs from the same gene. To avoid such duplication, ESTs are usually derived from the 3'-untranslated regions of the mRNA.

Mapping of Sequence Tagged Sites

To map STS or EST sites a collection of chromosome fragments is examined for the presence of each STS or EST (Fig. 24.18). The fragments may be derived from a single chromosome or the whole genome. The chance that any two STSs will be on the same

PCR primer

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