The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
All other sections in this Literature Study Guide are owned and copyrighted by BookRags, Inc.
Sequence-tagged sites (STSs) are short stretches of DNA sequence, usually a few hundred bases long, which can be amplified by the polymerase chain reaction, and are regarded as landmarks in a genome. Presence of a specific STS in a genomic clone or DNA from a specific chromosome can be tested by PCR. STSs are most useful when they have been mapped to a specific chromosome using somatic cell hybrids and to a specific region by screening cell hybrids containing fragments of human chromosomes. An STS map is a collection of STSs ordered along a chromosome with their physical position known. They are used to orientate and order genomic clones such as BACs and YACs in order to generate physical maps. STS maps have been generated for the human genome as part of the human genome project. They have also been generated for other organisms such as the mouse and the zebrafish, usually as a precursor for full genomic sequencing.
STSs can be generated in different ways. Many STSs were generated for the human genome by sequencing a few hundred bases of both ends of BACs. Other STSs were generated by randomly cloning and sequencing small fragments of the human genome. STSs were also generated for the human genome when simple tandem repeat sequence markers (microsatellites) were isolated for genetic mapping. These STSs are therefore used as physical markers and as genetic markers, providing a link between physical and genetic maps.
Clones containing a certain STS can be isolated by screening genomic libraries by PCR. This is an alternative to screening genomic libraries by hybridisation with the STS used as a radioactively labeled probe. The PCR-based screening method is labor-intensive and false negatives are more common in PCR compared to hybridization, so the hybridization method is more commonly used.