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Cloning – In the Eyes of the Beholder Ida Chow, Ph.D. Society for Developmental Biology Bethesda, Maryland Society for Developmental Biology

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cloning in the eyes of the beholder

Cloning – In the Eyes of the Beholder

Ida Chow, Ph.D.

Society for Developmental Biology

Bethesda, Maryland

society for developmental biology
Society for Developmental Biology

The Society for Developmental Biology declares a voluntary five-year moratorium on cloning human beings, where ‘cloning human beings’ is defined as the duplication of an existing or previously existing human being by transferring the nucleus of a differentiated, somatic cell into an enucleated human oocyte, and implanting the resulting product for intrauterine gestation and subsequent birth.Sept. 1997. Extended Jan. 2003

  • Greek klon = twig (cuttings from one original plant)
  • Molecular biology: copies of DNA (gene) fragments
  • Cell cultures: cell multiplication by cell division (mitosis)
  • Bacterial growth
  • Plants budding
  • Identical twins
  • Identical genetic copies
fundamental question
Fundamental Question

How does a single cell, the fertilized egg, transform into a complex organism, with many different types of cells, tissues and organs?

- processes?

- genes?

- control / regulation?


Totipotency– Capable of giving origin to all the cell types in the organism, person, e.g., fertilized egg developing into a whole organism

  • Gradual loss of the capability for differentiation with the process of development - Pluripotency, multipotency, e.g.,superficial skin cell from deep layer skin cell
  • Somatic cells: body cells, full genetic complement, 2 sets of chromosomes = diploid, 46 in humans
  • Germ cells: gametes, oocyte (unfertilized egg) and sperm, one half of genetic complement, 1 set of chromosomes = haploid, 23 in humans
  • Fertilization = fusion of sperm and oocyte, full genetic complement, 1 set of chromosome from egg and 1 from sperm, diploid
somatic cell nuclear transfer
Somatic Cell Nuclear Transfer
  • Removal of the nucleus containing the genes of an unfertilized oocyte
  • Fusion of an isolated body cell with the oocyte, or injection of the somatic cell nucleus into the oocyte
  • Stimulation of the oocyte to begin the process of cell division and differentiation, producing the blastocyst (a hollowed ball with a mass of about 150 cells)
fundamental questions
Fundamental Questions
  • Reprogramming of gene expression: How to make the adult somatic cell nuclear DNA (genes) express the same way as in an embryo, that is, following the proper sequence.
  • What molecules in the oocyte cytoplasm are capable of

de-differentiating the adult somatic cell nucleus?


unlimited capability for cellular reproduction

broader pluripotency

more direct access to stem cells

large number of available stem cells

many identified inducing factors


limited capability for cellular reproduction

limited pluripotency

difficult access and identification of the stem cells

limited number of available stem cells

chromosomal defects

reproductive cloning
Reproductive Cloning
  • Implantation of the blastocyst into a prepared womb of a female
  • Further differentiation and growth of the cloned product
  • Delivery of a full-term (or almost) cloned individual, with nuclear DNA identical to that of the donor of the body cell, and mitochondrial DNA identical to that of the oocyte; no genetic similarity to surrogate female if not oocyte donor
Figures in this presentation are from publications by the

National Institutes of Health ( ):

Stem Cells: a Primer (

Stem Cells: Scientific Progress and Future Research Directions


additional resources
Additional Resources
  • Society for Developmental Biology (SDB):, Focus on Stem Cells:
  • National Institutes of Health (NIH):, Stem Cell Information Index:
  • National Bioethics Advisory Commission Reports (NBAC): Scrawl done and see the following reports: Ethical Issues in Human Stem Cell Research(Sept. 1999) and Cloning Human Beings (June 1997)
  • The President’s Council on Bioethics (PCBE):, and see the Cloning Report:
  • The National Academies: Scientific and Medical Aspects of Human Reproductive Cloning:, Stem Cells and the Future of Regenerative Medicine:
  • Federation of American Societies for Experimental Biology (FASEB):, Cloning, Past, Present and the Exciting Future: