Retrotransposons: bringing disco back?

Sorry about the cliffhanger in the last post. I lied, I'm moving on to a new topic today: the humble retrotransposon, although its hardly humble considering 48% of our genome is made up of transposons or their remnants. A retrotransposon is a piece of DNA that doesn't code for a protein (no DNA codes directly for proteins, but you know what I mean), but it codes for an abnormal piece of RNA. It can roam the genome freely, unlike most other RNA molecules. They can replicate infinitely using this RNA intermediate, and thus increase the frequency of certain elements of the genome. But how exactly do they do this as RNA? Well, it does this by breaking the rules. The biological dogma states that DNA codes for RNA, which codes for proteins, and they code for nothing. However the retrotransposon can use an enzyme known as reverse transcriptase, which it codes for, to become deoxyribonucleic acid again. Retroviruses can also do this with their genetic material (hence the 'retro' in their names). Retrotransposons can induce mutations, and cause malfunction in gene regulating mechanisms by inserting themselves between, or even directly into genes, which makes them useful for studying epigenetic mechanisms like DNA methylation. In mice for example the variation in expression of a retrotransposon due to methylation affects expression of the agouti coat colour gene, as usually RNA from retrotransposons messes up control of downstream agouti gene keeping it switched on continuously, leading to coat colour variability between genetically identical individuals, purely due to molecular modifications to the DNA. Furthermore, the mutations introduced by retrotransposons are very stable, because the base sequence at the insertion site stays constant as they transpose via semi-conservative DNA replication. As retrotransposons age they often accumulate mutations, and so are unable to retrostranspose. Transposition and survival of retrotransposons within the host genome are regulated both by retrotransposon- and host-encoded factors, to avoid deletion of elements of the retrotransposon and the host genome, in a symbiotic relationship that has existed for millions of years between retrotransposons and their hosts. The study of how retrotransposons and their host genomes have co-evolved mechanisms to regulate; transposition, specific insertion sites, and mutational outcomes to optimise each other's survival is still a developing field, which I find quite amazing, considering that the retrotransposons represent about 50% of our genome. We don't even know if most of them do anything, they're almost like outsiders in our own bodies...