-
August Weismann
August Weismann, professor of zoology and comparative anatomy at the University of Freiberg, theorized that the genetic information of a cell would diminish as the cell went through differentiation. -
Wilhelm Roux
Wilhelm Roux tested the germ plasm theory for the first time. One cell of a 2-cell frog embryo was destroyed with a hot needle; the result was a half-embryo, supporting Weismann's theory. -
Hans Dreisch
Hans Dreisch isolated blastomeres from 2- and 4-cell sea urchin embryos and observed their development into small larvae. These experiments were regarded as refutations of the Weismann-Roux theory. -
Hans Spemann
Hans Spemann split a 2-cell newt embryo into two parts, resulting in the development of two complete larvae. -
Hans Spemann
German embryologist Hans Spemann split a 2-celled salamander embryo and each cell grew to adulthood, providing proof that early embryo cells carry necessary genetic information. This finally disproved Weismann's 1885 theory that the amount of genetic information in cells decreases with each division -
Walter Sutton
Walter Sutton published "On the Morphology of the Chromosome Group in Brachyotola magna", hypothesizing that chromosomes carry the inheritance and that they occur in distinct pairs within a cell's nucleus. Sutton also argued that how chromosomes act when sex cells divide was the basis for the Mendelian Law of Heredity -
Hans Spermann
Hans Spermann conducted and early nuclear transfer experiment. -
Hans Spemann
Hans Spemann performed further, successful nuclear transfer experiments. -
Hans Spemann
Hans Spemann published the results of his 1928 primitive nuclear transfer experiments involving salamander embryos in the book "Embryonic Development and Induction." Spemann argued the next step for research should be the cloning organisms by extracting the nucleus of a differentiated cell and putting it into an enucleated egg -
Oswald Avery
Oswald Avery found that a cell's genetic information was carried in DNA. -
freezing of bull semen
First successful freezing of bull semen at -79°C for later insemination of cows was accomplished -
Robert Briggs and Thomas J. King
First animal cloning: Robert Briggs and Thomas J. King cloned northern leopard frogs. -
Francis Crick and James Watson
Francis Crick and James Watson ,working at Cambridge's Cavendish Laboratory, discovered the structure of DNA -
Biologist John Gurdon
Biologist John Gurdon announced that he had cloned South African frogs using the nucleus of fully differentiated adult intestinal cells. This demonstrated that cells' genetic potential do not diminish as the cell became specialized. -
Robert G. McKinnell, Thomas J. King, and Marie A. Di Berardino
Robert G. McKinnell, Thomas J. King, and Marie A. Di Berardino produced swimming larvae from enucleated oocytes that had been injected with adult frog kidney carcinoma cell nuclei. -
Biologist J.B.S
Biologist J.B.S. Haldane coined the term "clone" in a speech entitled "Biological Possibilities for the Human Species of the Next Ten-Thousand Years." -
F.C. Steward
F.C. Steward grew a complete carrot plant from a fully differentiated carrot root cell.
