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10-31-11 Neverending Genes and Develoment II

10-31-11 Neverending Genes and Develoment II - ZOL 320...

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ZOL 320 Developmental Bio October 31, 2011 Genes and Development II Continued (It’s like it never ends.) II. Nuclear totipotency – Do somatic cells retain all zygote DNA in unchanged form (i.e. have genomic constancy?) A. Nuclear transplantation in amphibians a. Main test : If a nucleus from a differentiated cell was used in place of the zygote nucleus and development occurred normally, then that donor nucleus would be proven totipotent. b. Amphibian nuclear transplantation methods: b.i. In donor versus host experiments the donor must be identifiable with a nuclear marker and with a differentiation marker. b.ii. Steps in nuclear transplantation experiment: b.ii.1. Enucleation of oocyte b.ii.2. Transplantation of somatic nucleus b.ii.3. Allow parthenogenetic development b.iii. Key point: The oocyte cytoplasm is “dominant” to the nucleus . The nucleus begins to express genes appropriate to early development and not those of the original cell. b.iv. “totipotency” depended on age of donor cell (older nuclei were less totipotent) b.v. Healthy, viable cloned frogs descended from one tadpole intestinal lining donor cell nucleus used for multiple nuclear transplants. b.vi. Conclusions from frog nuclear transplantation experiments: b.vi.1. In all but a few transfers, the nuclei could not support full development of a fertile adult. Many nuclei from differentiated cells, however, gave rise to viable tadpoles indicating high pluripotency.
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