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Transposons: Definition & Types

Instructor: Catherine Paul

Catherine has taught high school science and has a master's degree in biology.

Explore the motile world of genetics by learning more about the 'jumping genes' called transposons. Plentiful in many organisms, transposons have an active role in mutations, antibiotic resistance, and disease.

What are Transposons?

When we think of our genetics, we imagine the DNA that codes for our genes. But we may not realize that these genes are not motionless: small fragments of DNA can actually move! Some genes, called transposons, or 'jumping genes', can transfer themselves across separate structures of DNA called chromosomes. In fact, the name 'transposon' closely resembles their ability to 'transpose'. These genes are sometimes referred to as a transposable element (TE). Imagine genes jumping from one chromosome to another, just as a monkey jumps from tree to tree!

Discovery of Transposons

Nobel Prize winning scientist, Barbara McClintock, first discovered transposons in the 1940's. While she was studying maize genetics, she noticed how separate kernels of corn displayed different colors in the same cob. Her research revealed that each corn kernel looked different because it was genetically different. McClintock understood that this could only occur if the genes were not stationary, but mobile, and able to 'jump' from one chromosome to another.

Transposons in Maize
Transposons in Maize

Barbara McClintock concluded that as transposons change from one location to another, they affect which genes are expressed. During her research, transposons were able to turn on or shut off genes in each kernel, which led to color variation to the corncob, or a mutation. A mutation occurs when any genetic change happens in DNA, or if chromosomes are altered. If a transposon jumps within a gene then, a mutation has occurred, and that specific gene may be inactivated. What is fascinating about transposons is that, depending on how they 'jump', they can cause a new mutation or shut off a previously existing mutation.

Transposons Are Common

TEs are much more common than we might assume. For example, approximately 90% of wheat DNA and 85% of corn DNA is made of transposons. Half of our own DNA most likely consists of transposons. Many transposons are actually copies of the same genes that repeat themselves. Because of their ability to turn on or off genes, mutations caused by transposons play a role in the evolution of organisms.

The spontaneous jumping of transposable elements into random genes has been associated with disease. For example, Hemophilia A and B, severe combined immunodeficiency (SCID), and Duchenne muscular dystrophy are caused by transposons; TEs may also contribute to colon cancer. Transposons exist in many species, such as bacteria. For instance, microbes contain transposons in their chromosomal DNA, or in a separate piece of circular DNA called a plasmid. Plasmids are frequently exchanged between bacteria and can provide bacteria with genes for antibiotic resistance and toxins that can cause major health problems.

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