Download Transplantation Experiments: Each cell contains a full set of genetic

Transplantation Experiments:
Each cell contains a full set of
genetic instructions
Created by: GPS
• A test was carried out in 1952 by American
Embryologists Robert Briggs and Thomas
King
• Tested the hypothesis resulting from the
Hammerling’s experiments
• The nucleus is the location of all heredity
information in a cell
•The Procedure
•Briggs and King removed the nucleus from a frog egg
using a glass pipette and a microscope. Could also be
destroyed by UV light.
•The egg did not develop
•When the nucleus was replaced with one removed from a
more advanced frog embryo cell…
•The egg developed into an adult
•Result: The nucleus was directing the eggs development
into an adult frog
Can every nucleus in an organism
direct the development of an
entire adult individual?
•This was not answered definitely, because the
nuclei they transplanted from frog embryos into
eggs often caused the eggs to develop abnormally
•Soon afterward, two more experiments were
performed
Successfully Transplanting
Nuclei
•John Gurdon (worked with South African clawed frogs
("Xenopus laevis") at Yale and Oxford) transplanted nuclei
from a tadpole cell into eggs from which the nuclei had been
removed.
•It was necessary to synchronize the division cycles of donor
and host.
•In many of these experiments, the eggs developed normally.
•Indicates that the nuclei of cells in later stages of development
retain genetic information necessary to direct development of
all other cells in an individual.
John Gurdon
•In 1962, Gurdon announced that he had used the nucleus of fully differentiated
adult intestinal cells to clone South African clawed frogs ("Xenopus laevis"). This
was the first demonstration in animals that the nucleus of a differentiated somatic
cell retains the potential to develop into all cell types. Is totipotent and paved the
way for future somatic cell nuclear transfer experiments, including the 1996
cloning of the sheep, Dolly.
•Gurdon believed that the tadpoles were old enough so that cells taken from them
would be differentiated. He exposed a frog egg to ultraviolet light, which
destroyed its nucleus, then removed the nucleus from the tadpole intestinal cell
and implanted it in the enucleated egg. The egg grew into a tadpole that was
genetically identical to the DNA-donating tadpole, but the tadpoles cloned in early
experiments never survived to adulthood. In later work, however, Gurdon
successfully produced sexually mature adult frogs from eggs into which
genetically marked nuclei had been transplanted from differentiated tadpole cells.
Totipotency in Plants
•F.C. Steward (Cornell University in 1958) placed
small fragments of fully developed carrot tissue
(isolated from part of the phloem) in a flask
containing liquid growth medium.
•Observed that when individual cells broke away
from the fragments, they divided and developed
multicellular roots.
Totipotency in Plants Continued..
•Steward immobilized the roots by placing them in a solid
growth medium.
•The roots developed normally into entire, mature plants
•Results: Even in adult tissues, the nucleus of individual
plant cells are “totipotent” meaning that each contains a full
set of heredity instructions and can generate an entire adult
individual.