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
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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