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The Genetic Management of Endangered Species
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15037 |
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Section : |
NATURAL SCIENCE
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9 / 1988 |
2,552 Words |
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Dwight G. Smith
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The task of saving a critically endangered species is becoming a science that follows a familiar formula. Years of painstaking attention to the propagation of animals and birds nearing extinction has begun to yield proven procedures for preserving endangered species. Two of the key steps are (1) establishing a captive breeding colony to maximize the production of eggs and young by tested captive propagation methods, and (2) releasing suitably mature young into a safe habitat to augment numbers in the wild.
To enhance the species' recovery, new techniques are continuously being tested and added. The newest and most promising of these utilizes recent developments in biotechnology to assist in the genetic management of endangered species. This high-tech management may ultimately lead to selective breeding programs that will result in vigorous offspring, well adapted to the demands of a human-modified environment. For now, genetic engineering allows scientists to develop pedigree charts which are used to guide the mating of captive pairs. This solves one of the long-standing problems in the management of almost every endangered species--the tendency for inbreeding in small populations whose few closely related individuals are likely to mate and produce genetically disadvantaged offspring.
All of the nearly 200 whooping cranes alive today, for example, are the descendants of the 15 individuals which comprised the entire migratory population in 1941. Similarly, all future California condors will be the offspring of the 28 now in captivity [see "The Eclipse of the California Condor," THE WORLD & I, February 1988]. These and other endangered species with small populations, such as the black-footed ferret, key deer, and red wolf share the risks of a high probability of inbreeding, which increases with each generation.
When closely related individuals mate, the chances of offspring inheriting the same deleterious genes from each parent increases. Deleterious genes are the product of randomly occurring mutations that affect every population. All humans, for example, probably carry at least one mutation in their chromosomal makeup. Mutations increase a population's genetic variability and are the raw stuff of evolution. However, the great majority of mutations are potentially harmful, but are usually hidden by the presence of normal genes. When related individuals mate, however, their offspring may inherit a double dose of these genes and be negatively affected. (Perhaps the first taboo against incestuous marriages among humans arose because of the natural consequences that followed such matings.)
For captive breeding populations the consequences of genetic deficiencies are especially important, because they often reduce the productivity of mated pairs: Fertility is lower, fewer young are produced, young exhibit abnormal growth and an abnormally high mortality rate, and both young and adults are plagued by various behavioral and physiological abnormalities.
Applied genetic engineering may reduce or entirely eliminate these problems and, in time, will probably prove to be the most valuable of the many techniques used to save an endangered species.
Species Recovery And Captive Propagation
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