The theory of 'jumping genes' (transposons) was proposed by:

Barbara McClintock (1902-1992) was an American scientist and one of the most important geneticists of the 20th century. She studied the genetics of maize (corn) at the Cold Spring Harbor Laboratory in New York.

In the late 1940s, while studying the colour patterns of maize kernels, which can be speckled or streaked with different colours, McClintock discovered that certain genetic elements could move from one position on a chromosome to another. When these elements moved, they could switch nearby genes on or off, changing the colour of the kernels. She called them "controlling elements". Today they are known as transposable elements or transposons, popularly called "jumping genes". She published her findings in 1950-1953.

At first, her ideas were not widely accepted, because most scientists then believed that genes had fixed positions on chromosomes, like beads on a string. Only in the 1970s, when transposons were discovered in bacteria and other organisms, did the importance of her work become clear. She was awarded the Nobel Prize in Physiology or Medicine in 1983, alone, for "her discovery of mobile genetic elements". She was the first woman to win an unshared Nobel Prize in that category.

Transposons are now known to make up a large part of the genomes of many organisms; nearly half of the human genome consists of transposable elements and their remains. They are important in evolution, genetic variation and the spread of antibiotic resistance in bacteria, and they are used as tools in genetic engineering.

Why not the other options?

• ✗Gregor Mendel discovered the laws of inheritance using pea plants and is called the father of genetics.
• ✗Thomas Hunt Morgan proved the chromosome theory of inheritance and discovered linkage using fruit flies (Drosophila); he won the Nobel Prize in 1933.
• ✗Rosalind Franklin produced X-ray images of DNA (Photo 51) that helped reveal its double-helix structure.