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Post by Ajay » Sun May 07, 2006 5:55 pm

I read from a text that transposons are mobile genetic sequences which can change from one position to another. Will this not alter the DNA sequence in an individual ?

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Post by dae » Sun May 07, 2006 8:08 pm

Sure will, if the individual is a cell. Transposons work intracellularly but several cells, or the entire multicellular organism, can have transposons. In the process of their "jumping" they can cause mutations and alter the total amount of DNA in the cell. According to wikipedia, approximitly 45% of the human genome is composed of transposons or their defunct reminants.

There are two types that we know of:
Class 1 are Retrotransposons that work via a "copy-and-past" mechanism were the retrotransposon is transcribed then copies itself back into the genome in several places using reverse transcriptase (which is often coded for by the retrotransposon itself).
Class 2 are DNA Transposons that work via a "cut-and-past" mechanism were a transposase inserts them into different parts of the genome.

Both of these classes can loose their ability to produce a working enzyme via mutation but can still be copied and inserted or moved throughout the genome by enzymes produced by other, working, transposons.

There is a wealth of information on the subject that is easily locatable if you're still interested.

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Post by LilKim » Sun May 07, 2006 9:55 pm

Transposon jumping can disrupt genes in the cells in which the transposition occured. The jumping basically causes a sizable DNA insertion that expands a gene and generally renders it non-functional.

So, if transposon exists in a transcriptionally silent region of the genome.. and "jumps" into a gene that is very active ... it will disrupt the function of that resultant gene.

Transposable elements have been used extensively in drosophila genetic screens. For example, if a transposable element jumps into a gene necessary for drosphila eye development... the resulting fly will probably live but have an eye deformation (because the gene necessary for development is disrupted)... at that point, drosphila geneticist can try to determine WHICH gene was disrupted by the transposable element.. which would give them the identity of the gene necessary for eye development.

As far as in the human/mammalian genomes there are NUMEROUS NUMEROUS NUMEROUS mechanisms that prevent transposition.. so it RARELY occurs!!! (uncontrolled transposition is lethal)

... anyyways, i want to keep my explanation simple. If you need additional clarification... please let us know!

buena suerte!

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