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Solomon IM Ch 17

Solomon IM Ch 17 - ,Berg,andMartinsBiology,9thEdition 17...

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Instructor’s Manual for Solomon, Berg, and Martin’s Biology, 9 th Edition 178 17 Developmental Genetics Lecture Outline I. Cell differentiation usually does not involve changes in DNA. A. All of the 200 differentiated cells in a human body descended from a single fertilized egg cell (zygote). 1. With a few exceptions, cells do not lose genes that are not needed. 2. Nuclear equivalence is a concept that describes the genetic similarity of all cells in a multicellular organism. a) The somatic cells in an adult animal have the same genes. b) Totipotent cells provide the evidence for nuclear equivalence. B. Differential gene expression determines which genes are turned on in which cells to make certain proteins. 1. Differentiation of cells requires differential expression of the products produced through transcription and translation in different types of cell. C. A totipotent nucleus contains all the instructions required to direct development. 1. Plant tissue culture is based on totipotent plant cells, first developed by Steward and colleagues in the 1950s. a) Tissue culture is of importance in biotechnology. b) Cells are induced to divide, then are transferred to agar where they grow into an entire plant. c) Plantlets can be cloned in this way from genetically engineered plants. 2. Totipotency in animal cells has not been as successful as in plant experimentation. a) Nuclei from amphibian cells have been successfully transplanted into egg cells. D. The first successful cloning of a mammal occurred in 1996 and resulted in the sheep Dolly. 1. Dolly was the result of a cultured mammary gland cell from an adult sheep that was fused with an enucleated sheep egg. 2. There has been low overall success rate to date, partly due to the fact that it is difficult for the cell cycles of the donor cell and the recipient cell to be in synchrony. 3. Transgenic organisms, in which foreign genes are introduced, have been the subject of most cloning research. a) Research is attempting to improve the efficiency of this technique and widen its horizons. b) In human therapeutic cloning, no newborn human is developed. c) The primary purpose of human therapeutic cloning is to produce stem cells. E. Stem cells divide and give rise to differentiated cells. 1. Totipotent cells can give rise to all tissues of the body.
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Chapter 17: Developmental Genetics 179 2. Pleuripotent stem cells are more specialized and give rise to cells of the line to which they belong; e.g., pleuripotent neural stem cells give rise to various types of brain cells. 3. Stem cells have the potential for transplantation into humans with degenerative diseases such as Parkinson’s. 4. Most of these studies are funded by private companies because of governmental restrictions on stem cell research.
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