The first theories and experiments with cloning began in the late 1880s as scientists sought to prove their theories about how the genetic material inside cells worked. The earliest experiments involved splitting the embryos of frogs and salamanders to see how the resulting animals would develop. As chromosomes became better understood, more experiments were done with cloning, resulting in the first cloned animals in 1952.
History
Discoveries about the nature of DNA in the 1940s made it possible for cloning experiments to progress. In 1944 it was discovered that genetic information for each cell was kept in the cell's DNA. When Oswald Avery found this genetic information, it gave scientists new ways to try to clone animals by using that genetic blueprint.
Types
The first cloned animals were northern leopard frogs that were cloned in 1952. Thomas J. King and Robert Briggs cloned 35 frog embryos and saw 27 tadpoles hatch. This first successful cloning taught scientists more about what cells needed to be used in the cloning process. King and Briggs believed, based on their clones, that young cells were more viable for the cloning process. Cells that were taken from adults resulted in abnormally developed tadpoles.
Significance
The next successful cloning experiments also resulted in cloned frogs. John Gurdon cloned South African frogs in 1962. His use of adult cells disproved the prior theory that only young cells could be used in the cloning process with success. From 1962 to 1965, Thomas King, Robert McKinnell and Marie Di Berardino created more frog clones from adult frog cells.
Considerations
While animal cloning had been the focus of cloning experiments, the 1960s also saw other types of cloning. In 1964 F.C. Steward took an adult root cell from a carrot plant and successfully cloned the plant. Throughout the rest of the 1960s, scientists continued to clone frogs and to discover more about DNA. The first gene was discovered in 1969.
Potential
In 1977, the first cloned mice were created. Mouse cloning research continued, and new cloned mice were created in 1979. The first mammal was cloned in 1984. The cloned sheep was quickly followed in 1985 with cloned cattle embryos. A cow clone was created in 1986 and several calves in 1993. That same year, human embryos were cloned for the first time. In 1995 and 1996, sheep were cloned, including the famous Dolly. Since Dolly's creation, the cloning of mice and other small animals has continued, but human cloning research has been banned in many countries.
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