Question

In your own words, discuss the role that transposons may have played in the evolution of modern organisms. What is exon shuffling? What role do transposons play in the process of exon shuffling?

Answer 1

Recently it is proven that some of the transposons are essential for an organism to survive and also played a vital role in the evolution of a multicellular organisms.

The discovery of transposons in 1950's, they are treated as a culprit for producing mutations. The transposons are found in almost all types of orrganisms and species on earth,either in active form or inactive form. The transposons can be divided into two broad categories.

• Class I Transposons, a retro transposons found in almost all eukaryotes.
• Class II Transposons ,DNA Transposons found in prokaryotes.

RNA Mediated transpositions is performed by the retro transposons and through a reverse transcription, a newly formed DNA is inserted into the genome. Contrary , the DNA Transposons directly inserted into the target site. Transposons are just a bunch of a junk DNA without an apparent regulatory function in the genome although they can encode protein for themselves.

Exon Shuffling

Exon Shuffling is molecular mechanism for the formation of new genes.It is a process through which two or more exons from different genes can be brought together ectopically or the same exon can be duplicated to create a new exon intron structure. Different mechanism for exon shuffling are ;

• Transposons mediated exon shuffling
• Cross over during sexual recombination of parental genome.
• Ilegitimate recombination

Role of Transposons in the process of Exon Shuffling

Transposons are long regions of DNA similarity that can stabilize synapsis,, increasing the chances of unequal recombination and exon shuffling. For example, Alu elements are often found within introns, were they can integrate with no ill effects. The similarity of Alu elements in the introns of unrelated genes does seem to account for exon shuffling by unequal crossing over between the different genes that share domains and specific functions as a result. Trnsposons will also facilitate germ line cell exon shuffling more directly.

DNA Transposon-Mediated Exon Shuffling Gene 1 Con Gene A3 DNA gene1, DNA transposon exon 2 transposon gene 1, transposase excised transposon transposase gene 2 exon Gene BE Transposons flanking gene 1/exon 2 inserts into gene 2 Gene B Gene B now encoded a protein with a new structural feature conferring potential new function on the protein.