Transposable elements are mobile pieces of genetic material that can create new genes, making them important in evolution. They can cause disease by disabling functional genes or leaving gaps. American scientist Barbara McClintock discovered them in maize. There are two types: retrotransposons and DNA transposons. Bacteria and eukaryotes have defensive mechanisms against excessive genetic change. The evolution of transposable elements is not well understood, but they are found in all major branches of life.
A transposable element, or transposon, is a moveable piece of genetic material. These deoxyribonucleic acid (DNA) sequences are replicated multiple times within a genome or are shifted into their original form. Because of their ability to create new genes, transposable elements are considered mutagenic and are an import device in evolution. Transposable elements are being studied to help better understand genetic change and the causes of disease.
American scientist Barbara McClintock first discovered the transposable element towards the end of World War II. She has studied the reproduction methods of maize, or maize, with a focus on how chromosomes change. She also produced the first genetic map for corn. Her research was initially met with skepticism. It wasn’t until 1983 that she was awarded a Nobel Prize for her work.
The first possible method of mobility for a transposable item is similar to the “copy and paste” function on a computer. These types of transposable elements are classified as Class I and are sometimes called retrotransposons. In this mode of replication, a ribonucleic acid (RNA) intermediate is used. Retrotransposons are particularly abundant in plants and other eukaryotes, or organisms with complex cells. Nearly half of the human genome is made up of this form of transposable element.
DNA transposons are the second type of transposable element, classified as Class II. Instead of using an RNA intermediate, Class II elements generally use enzymes in a similar “cut and paste” process. Enzymes are types of molecules that help speed up chemical reactions in an organism. DNA transposons are less common in the human genome than retrotransposons, but still play an important role in evolution.
Transposable elements are known to cause disease. Hemophilia A and B, a predisposition to cancer, and a type of muscular dystrophy can all be caused by this type of change in genetic material. If a transposable element is inserted into a functional gene, it can disable the entire gene. If a gap in a gene is left by an outgoing DNA transposon, the gene is usually not repaired properly.
Cells typically have defensive mechanisms against excessive genetic change. Bacteria can routinely clear large portions of their genome as protection against the spread of viruses and transposable elements. Eukaryotes can use RNA molecules in their cells to interfere with the activity of transposable elements. These measures are evolutionary adaptations to help keep new mutations in check.
The evolution of transposable elements is not well understood. Some believe that the phenomenon arose early in the evolutionary history of life and was passed down to later species. Others argue that the elements originated multiple times independently of each other. Another possibility is that transposable elements evolved more recently and spread to different life forms through a process called horizontal gene transfer. In any case, transposable elements are found today in all major branches of life.
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