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.
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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.
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Disruptive selection is a special form of directional selection. By choosing two phenotypic extremes within a population, successive breeding can be carried out to produce two discontinuous strains. For example, if a plant breeder breeds the longest and the shortest seeds within a population, then after several generations two different strains would be produced: one bearing long seeds and the other bearing short seeds. The strains would be morphologically dissimilar in respect of their seed lengths, but they would be the same in all non-linked effects.
Disruptive selection forces the organism to produce two different forms. When it occurs under natural conditions, disruptive selection can be the first step on the production of two different species. An example of this occurrence could be seen if a river drove its path through a population of plants. The plants cannot move so they have to adapt or die out under the new conditions. Within the population, some individuals may be better suited to waterlogged conditions and will thrive at the riverbed. Other individuals living the furthest from the water may be better suited to dryer conditions. The alteration of the river's course forces a wedge within the population, producing two rapidly diverging forms of the plant species.