Have you ever heard of “jumping genes?” I recently did in my studies of genomic evolution. Behind the discovery of these genes was Barbara McClintock, the 1983 Nobel Prize winner in Physiology or Medicine.
She grew up in the Northeastern region of the United States. In 1919, she began her studies at Cornell's College of Agriculture. She never married, choosing to devote her life to research instead.
McClintock studied genetics through corn, for example the different colors of its kernels. She studied how these characteristics are passed down through generations and linked this to changes in the plants' chromosomes. During the 1940s and 1950s, she proved that genetic elements can sometimes change position on a chromosome and that this causes nearby genes to become active or inactive.
These stretches are known as transposable elements, or “jumping genes,” but they actually never completely detach from the cell’s DNA. These segments of DNA can move within the genome with the aid of a DNA or RNA intermediate. Thus, they are considered significant in understanding genomic evolution and genetic diversity. Surprisingly, about 75% of repetitive DNA (44% of the human genome) is made up of transposable elements and sequences related to them (Campbell Biology in Focus).
As she tracked corn plants through multiple generations of experiments, McClintock identified changes in the color of corn kernels that made sense only if she “postulated the existence of genetic elements capable of moving from other locations in the genome into the genes for kernel color, disrupting the genes so that the kernel color was changed” (Campbell Biology in Focus). Her findings were initially met with great skepticism. But, they were eventually validated many years later when transposable elements were found in bacteria.
In 1983, at the age of 81, McClintock received the Nobel Prize for her pioneering research.