Question

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. Wow! It's amazing that this works!

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?

Answer 1

1) according to genomic equivalence principal all cells carry the same genetic information as carried by the single zygotic cell to encode an organism. In the dolly sheep example mature somatic cell nucleus encoded all information required for the full organism development. It suggests that during the sheep development and maturation all developmental and other genes were conserved throughout in the mature mammary gland cell nucleus and thus able to generate all cell types after fertilization.

2) nuclear reprogramming and cell cycle coordination control are two key elements that causes the low success rate of these experiments.

Age of the nucleus will then also affect the progeny because in each cell cycle to maintain the genetic information some portion were lost through telomere end loss. These telomere were associated with aging.

IN the matured nucleus epigenetic factors such as methylation and acetylation affects the gene expression at particular stage.

Different cell cycle control factors causes arrest of the particular cell type in coordination with their nuclear encoded information.

Other factors where the genomic equivalence will not work is in the case of t lymphocytes generation because there combinations were made through somatic rearrangement and reshuffling of the gene coding elements.