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.
Allele is the shortened, and more commonly used, form of the word alleleomorph. An allele is one of a series of possible forms of a given gene. Different alleles differ in their sequence of DNA, this difference can be as small as only one base pair change although it can be much larger. The difference must be such that the gene product, RNA or a protein, is different to the other form in an observable manner. Alleles are always at the same physical location (locus) on matching (homologous) chromosomes.
A diploid organism with two sets of identical alleles is termed homozygous, an organism with two different alleles is heterozygous. Several different forms of an allele can exist within a population, this is a phenomenon known as multiple allelism. Many genes occur in this manner, for example hair and eye color.
The first alleles studied in a scientific manner were those controlling varying characteristics of the pea. This work was undertaken by the Austrian monk, Gregor Mendel, in the late 1800s. Mendel studied a range of characters that were either present or absent, for example, smooth or wrinkled seed coats, tall or short plants or axial or terminal flowers. Each of these characteristics is governed by a single gene and in the plants that Mendel used only the two alleles were present, providing a very useable model to study this system.