Dr. Barbara McClintock was an American scientist. She extensively used maize (corn) as model system for her genetic studies. Maize has several advantages in genetic studies.

It has relatively larger chromosomes and Barbara McClintock developed method to stain and see maize chromosomes under microscope.

In maize artificial crossing (where pollen of desired plants are used to fertilized eggs of another desired plants) can be done easily and it gives rise to large number of seeds. When Barbara McClintock use to study maize genetics, structure of DNA was not known. Modern methods of studying genes did not exist. She took an approach of looking at the features of chromosome structures under microscope and link it to the plant phenotypes like colour of seeds.

Dr. McClintock noticed that on 9th chromosome a breakage happens at a particular site and as a result streaks of colour appears on the seeds which are normally uniformly light yellow in colour. This is because colour controlling genes are located near the breakage site. Not only that, this breakage is regulated by another piece of chromosome. She for the first time described that pieces of chromosomes where breaks happens and the piece of chromosome which regulate breakage are the moving parts of chromosomes. These are called transposons or popularly "jumping genes". She was awarded Physiology or Medicine Nobel prize in 1983 for her discovery of transposons.

Today we know, transposon exists in almost all organisms and in many cases they are the major part of total DNA of an organism.