Rucete ✏ Campbell Biology In a Nutshell
Unit 3 GENETICS — Concept 20.3 Cloned Organisms and Stem Cells Are Useful for Basic Research and Other Applications
Cloning technology and stem cell research have profound implications for basic biology and medical applications. Organismal cloning creates genetically identical organisms, while stem cell technology has the potential to regenerate damaged tissues and treat various diseases.
Organismal Cloning: Plants
In the 1950s, scientists cloned plants from single differentiated cells.
Mature plant cells retain full genetic potential; they can "dedifferentiate" and regenerate an entire organism.
This capacity to develop into all cell types is called totipotency.
Plant cloning is extensively used commercially (orchids, disease-resistant plants) and even commonly practiced at home (plant cuttings).
Organismal Cloning: Animals
Animal cloning is done through somatic cell nuclear transfer (SCNT):
Nucleus from a differentiated cell replaces the nucleus of an egg cell.
Egg develops into an embryo genetically identical to the donor cell.
Early experiments with frogs (1950s–1970s) by Robert Briggs, Thomas King, and John Gurdon demonstrated animal cell nuclei retain developmental potential, but efficiency decreases with cellular differentiation.
First mammal cloned from an adult cell was Dolly the sheep (1997):
Cloned from differentiated mammary gland cells.
Dolly developed health issues (arthritis, lung problems), possibly due to incomplete nuclear reprogramming.
Problems in Animal Cloning
Cloned animals frequently show developmental defects and health problems (e.g., obesity, premature aging).
Issues arise from incomplete epigenetic reprogramming (DNA methylation, histone modifications).
Successful cloning relies on reprogramming the donor nucleus to match embryonic gene expression patterns.
Stem Cells: Embryonic and Adult
Stem cells are unspecialized cells capable of self-renewal and differentiation into various specialized cells.
Embryonic stem (ES) cells (from blastocyst-stage embryos):
Pluripotent; can form virtually all cell types.
Easily grown in culture and directed to differentiate.
Adult stem cells:
Found in various tissues (bone marrow, brain, skin, etc.).
Limited potential; produce only specific cell types (e.g., blood cells).
Medical Potential of Stem Cells
Embryonic stem cells (ES) have enormous therapeutic potential due to pluripotency.
ES cells can theoretically regenerate damaged tissues or treat diseases (e.g., diabetes, Parkinson’s disease, spinal cord injuries).
Ethical concerns arise from using human embryos.
Therapeutic Cloning and Induced Pluripotent Stem Cells (iPS)
Therapeutic cloning uses nuclear transfer to produce ES cells matching a patient’s genetic makeup.
Induced pluripotent stem cells (iPS) are created by reprogramming differentiated cells (e.g., skin cells) to become pluripotent:
Achieved by introducing specific regulatory genes.
Can differentiate into many cell types; bypasses ethical issues associated with embryos.
iPS cells can be used to study diseases, test drugs, and regenerate damaged tissues personalized for each patient.
Research continues on optimizing safety, efficacy, and cost.
In a Nutshell
Cloning and stem cell technologies provide critical insights into developmental biology and offer revolutionary medical applications. While organismal cloning faces biological limitations and ethical debates, stem cell research—especially iPS cells—promises future therapeutic advancements personalized to patient needs.