Cloned and Transgenic Animals

Cloned and - Cloned and Transgenic Animals Except in very unusual situations sexual reproduction following meiosis insures that many diverse

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Cloned and Transgenic Animals Except in very unusual situations, sexual reproduction following meiosisinsures that many diverse genotypes will be present in the progeny. Theonly unusual situation that could be exploited in the past was"inbreeding", that is, the mating of closely related animals over successivegenerations. While inbreeding led to the creation of "breeds" such asJersey cattle that produce high amounts of butterfat and Holsteins thatproduce more milk but less butterfat, inbreeding can also cause problems.Crossing closely related organisms increases the risk that a detrimentalallele will become homozygous. Especially for animals such as cattle withlow rates of reproduction, the desire to "reproduce" genetically superiorindividuals has led to significant gains in applied reproductive technology.For example, artificial insemination (AI) using semen from "superior"bulls has been used commercially since 1937 in the dairy industry. (see http://www.asas.org/symposia/esupp2/Footehist.pdf for a history of AI) Naturally though, when a dairyman recognized a good cow, he wouldprefer to have more of her progeny in the future herd the one calf peryear that nature allows. One of the early discoveries that led to enhancedreproduction of select individuals was the concept of transferringembryos to a surrogate mother. Although done previously in rabbits, Dr.Berry here at TAMU (and associates) were the first to apply it to farmanimals, in this case transfers between goats and sheep, also in the 1930s.(If you are interested in this topic, look up "A history of farm animalembryo transfer and some associated techniques" by Keith J. Betteridgepublished in Animal Reproductive Science 79:204-244. You can access itfree on the WEB if on campus.) The idea was that early embryos could be removed from the natural motherand transferred to a less valuable female so the superior cow could breed againmuch sooner. Technological improvements have made the process relativelyefficient though still very
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This note was uploaded on 04/29/2008 for the course GENE 310 taught by Professor Magill during the Spring '08 term at Texas A&M.

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Cloned and - Cloned and Transgenic Animals Except in very unusual situations sexual reproduction following meiosis insures that many diverse

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