Cattle, sheep, rats, dogs, and several other species have been cloned using nucl

Question

Cattle, sheep, rats, dogs, and several other species have been cloned using nuclei from somatic cells. Embryos and adults produced by this approach often show a number of different mitochondrial defects. Explain possible reasons for the prevalence of mitochondrial defects in embryos created by nuclear transfer cloning. Use the following terms to fill in the blanks in the paragraph below:

oxidative phosphorylation, recipient, nuclear, substrate phosphorylation, nuclei, mitochondria, donor, nucleus, mitochondrial, heteroplasmic, homoplasmic

NOTE: Terms may be used more than once or not at all.

___(a) ____defects often involve processes of __(b) ____ and/or other essential mitochondrial functions that are dependent not only on the mitochondrial genome, but also on the _(c) _____ genome. When a __(d) ___genome is transferred, it may contain mutant genes that negatively influence __(e) ____ function that were compensated for in the original ___(f) __ cells, but not in the _(g) ____ cells. In addition, enucleated eggs invariably contain both normal and defective __(h) ___. When a __(i) ___ genome is transferred to an enucleated egg, __(j) ___ defects may arise from an uncompensated defective __(k) ___ genome, the _(l) ____ condition of the egg, or a combination of the two. A disease occurs when the __(m) ___ mutational load exceeds a tissue-specific threshold, which is generally low in highly metabolic tissues such as brain, heart, and muscle.

Explanation / Answer

Mitochondrial defects often involve processes of oxidativeand/or other essential mitochondrial functions that are dependent not only on the mitochondrial genome, but also on the nuclear genome. When a mitochondrial genome is transferred, it may contain mutant genes that negatively influence function mitochondrial that were compensated for in the original donor cells, but not in the recipient cells. In addition, enucleated eggs invariably contain both normal and defective nucleus. When a mitochondrial genome is transferred to an enucleated egg,mitochondrial defects may arise from an uncompensated defective mitochondrial genome, the heteroplasmiccondition of the egg, or a combination of the two. A disease occurs when the donormutational load exceeds a tissue-specific threshold, which is generally low in highly metabolic tissues such as brain, heart, and muscle.

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