The questions I get asked most often are:
- How many ERVs are there?
- How many do we have in common with chimpanzees/gorillas/orangutans/etc?
Its hard to answer this. Depends on what your definition of ‘ERV’ is. Because sometimes scientists mean a complete/nearly complete ERV (LTR–gag, pol, env–LTR), and sometimes they mean either LTR, Gag, Pol, or Env, or any combination. There are very few of the former, and a lot of the latter.
But how many are there total? Well, its hard to say. Sure, we sequenced the human (and chimpanzee, etc) genome, but we skipped a lot of the parts that are just stretches of repetitive DNA. Youll often find ERVs here, so youre missing them.
A group of scientists decided to do something fun– Look for ALL the ERVs in 18 different mouse strains:
And they found some cooooool stuff!
34,773 ERVs (and 28,951 SINEs, 40,074 LINEs)
They didnt find any ‘rabbits in the Precambrian‘– “This primary phylogeny matched the
phylogeny expected from the heritage of the mouse strains”. In other words, the ERVs were where they were supposed to be if evolution is true. Thank goodness. 😐
The half-life for an ERV to become a solo-LTR is about 0.8 million years.
There are fewer ERVs on the X-chromosome– 2/3 what you would expect if everything was random. “Male insertion bias”. heh. The authors say: “We propose that the vast majority of all TE insertions in the Mus lineage have occurred in the male germline genome.” Which kinda makes sense. A female is infected with a retrovirus, she has a set number of eggs that could become infected. A male is infected with a retrovirus, he can produce TONS of sperm infected with a retrovirus, and he has a lot more breeding opportunities.
ERVs are usually in junk DNA. Why? Cause its not as likely to kill the organism (and thus be selected against).
ERVs are in backwards. If this didnt matter, they would have expected a 50% to be going forwards, and 50% to be going backwards, but it was only 32.8% going forwards. Most were going backwards. Why? Think about your genes in your DNA like you read a sentence, from left to right. If your normal transcription machinery is reading left to right, and there is a retrovirus sitting there going left to right, your machinery might accidentally make a retrovirus. BAD. But if there is a retrovirus there, plopped in the opposite direction as your genes, your machinery is LESS likely to accidentally make babby retroviruses. Less likely to kill the organism.
What about the idea that ERV promoters, LTRs, are contributing to cellular gene expression levels? They really coudnt find any evidence of that, however, there might be something cell-specific that they just couldnt tease out with their methods.
So, ERVs are from the males, theyre backwards, they like junk, and they dont do anything useful. HA! HAHA!
BUT, the next time you want to stick it to a Creationist, and you want to use ERV data, use the mouse data. Its better.
- How many ERVs are there? 34,773
- How many do
wemice have in common with chimpanzees/gorillas/orangutans/etcother kinds of mice? All of them!