Transcript Genetics
Junk DNA • What is junk DNA for? – Less than 2% of DNA codes for proteins – Some of the rest has a purpose – Most appears to be completely useless • Evolution explains this perfectly – – – – DNA copying is a blind process It can be hijacked, e.g. by viruses It makes mistakes Mistakes accumulate over (lots of) time • Why would an omniscient designer create junk? – And why create the same junk in similar species? © Colin Frayn, 2008 www.frayn.net Endogenous Retriviruses • An ERV is an ancient virus that “wrote itself” into our genome – It does this by hijacking our own molecular apparatus – Uses ‘reverse transcriptase’ • This converts RNA of viruses into DNA • We share several of these with our most recent evolutionary ancestors – There are several thousand in the human genome • The more distant the ancestor, the fewer we have in common • Individual ERVs are mutated over time – This gives another excellent genetic clock – Identify the same ERV in to species and count the differences – More differences = longer since last common ancestor © Colin Frayn, 2008 www.frayn.net Glutamic acid in Haemoglobin • Alpha- and beta- chains of hemoglobin – These contain 12 codons for glutamic acid – Glutamic acid can be coded by either GAA or GAG • They both mean the same thing • All other things being equal, there’s no reason why to choose either over the other • So… it’s amazing that in all 12 positions, human, chimpanzee and monkey DNA use exactly the same variants – Except, of course, this is exactly what evolution predicts – We shared a common ancestor – We inherited the same DNA © Colin Frayn, 2008 www.frayn.net Haemoglobin alpha chains • This contains 141 amino acids – There are 20 to choose from so… – …probability against is 1:20141 • Is this massive number a disproof of evolution? • No, because: – Evolution is not random • Some strings are much more likely to evolve than others – Also, the current form is not the only plausible form • In fact, there are an estimated 20126 usable forms • So the probability of forming any one is 1:2025 • This is a certainty within evolutionary time • In fact, the similarity of haemoglobin strings in humans and other primates is a very string evidence for evolution. © Colin Frayn, 2008 www.frayn.net Cytochrome C • This is an enzyme • It is found in all living creatures • Differences (number of amino acids) in Cytochrome-C between humans and other organisms: Monkey 1 Chicken 18 Dog 13 Penguin 18 Horse 17 Turtle 19 Donkey 16 Rattlesnake 20 Pig 13 Fish (tuna) 31 Rabbit 12 Fly 33 Kangaroo 12 Moth 36 Duck 17 Mold 63 Pigeon 16 Yeast 56 © Colin Frayn, 2008 www.frayn.net