In $1997,$ Dolly the sheep was cloned by a technique called somatic-cell nuclear transfer (or nuclear-transfer cloning). A nucleus from an adult mammary cell was transferred into an egg from which the nucleus had been removed. The egg was allowed to divide several times in culture, then the embryo was transferred to a surrogate mother who gave birth to Dolly. Dolly died in 2003 after mating and giving birth herself to viable offspring. What does the creation of Dolly tell us about the potential of nuclear material derived from a fully differentiated adult cell? Does the creation of Doliy tell us anything about the potential of an intact, fully differentiated adult cell?
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The creation of Dolly tells us that the nuclear material derived from a fully differentiated adult cell has the potential to generate a new organism. This is because the nucleus from an adult mammary cell was able to direct the development of an embryo, which Show more…
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Scientists were successful in creating Dolly the sheep using the nucleus isolated from a differentiated cell from an adult mammary gland. They transferred this nucleus to an enucleated egg and activated the egg to start development. Thus, the adult mammary gland nucleus could replace the nucleus created in the 1 cell zygote from the fusion of the egg and sperm genetic material. 1) Describe in your own words how the success of reproductive cloning is able to demonstrate "genomic equivalence". 2) BUT....While this technique was successful in creating Dolly (and in a wide array of other species), it has a notoriously low success rate. Ignoring all of the technical reasons why this could fail (meaning ignoring all of the "scientist user error"), explain how the contents of the nucleus can contain the same genetic sequence but still not be functionally equivalent to the 1 cell zygote nucleus. What might be different between a mature nucleus and a zygote nucleus that results in the low success rate?
Shaiju T.
The sheep Dolly (Chapter 2 ) was the first cloned mammal. Dolly was created by implanting a nucleus from a cell taken from the udder of a female sheep into an enucleated egg. This nucleus had two X chromosomes, and because it came from a differentiated cell, one of them must have been inactivated. If the udder cell was heterozygous for at least one X-linked gene whose expression you could assay, how could you determine if all of Dolly's cells had the same $\mathrm{X}$ chromosome inactivated? If, upon testing, Dolly's cells prove to be mosaic for $\mathrm{X}$ chromosome activity-that is, different X's are active in different clones of cells-what must have happened during her embryological development?
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