Describe transposons.

Explanation

(i) Transposons are the DNA sequences which can move from one position to another position in a genome. This was first reported by an American Geneticist Barbara McClintock as "mobile controlling element" in Maize.
(ii) Barbara M Cl' k c mtoc when studying aleurone of single maize kernels, noted the unstable inheritance of the mosaic pattern of blue, brown and red spots due to the differential production of vacuolar anthocyanins.
(iii) In maize plant genome has AC / Ds transposon (AC = Activator, Ds = Dissociation). The activity of AC element is very distinct in maize plant. The transposition in somatic cells results in the changes in gene expression such as variegated pigmentation in maize kernels. Maize genome has transposable elements which regulated the different colour pattern of kernels.
(iv) McClintock's findings concluded that Ds and AC genes were mobile controlling elements. These are called transposable elements.
(v) McClintock gave the first direct experimental evidence that genomes are not static but are highly plastic entities.
Significance of transposons
(i) They contribute to many visible mutations and mutation rate in an Organism.
(ii) In evolution, they contribute to genetic diversity.
(iii) In genetic research transposons are valuable tools which are used as mutagens, as cloning tags, vehicles for inserting foreign DNA into model organism.