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The Silent Genome

Today I was reading about the human body which raised a few questions pertaining to the bodies anatomical quirks [which I will write about soon] but two stood out above the rest. They stood out because in each case they were mostly out of the control of our genome.The first trait I looked at is our fingerprints. They are an unmistakable gift from our primate ancestors. Primates [yes dear reader we are primates] are the only mammals with fingerprints. Before I go any further I can just see some budding young scientist or a cantankerous old one shaking their head and saying “nuuh, DNA controls everything about us.” Note I said they are mostly out of the control of our genome. The proof is quite simple. Just look at genetically identical twins, triplets or the mothers nightmare of 4 or more. None of them have the same fingerprints yet their genome is identical. Yes the genome is responsible for the fingers growing and separating [not exactly pretty when they are fused [as in simple or complex syndactyly]. Yet as seen above the genome isn’t responsible for the pattern. The genome is responsible for the growth of the ridges [arches, loops and whorls] but not for the selection of whatever pattern. What controls the pattern? Can’t say for sure but I can tell you it clearly isn’t determined by our genome. Incidentally, the fingerprints on your right hand are different from your left hand. It isn’t just no two people have the same fingerprints, it is no two finger have the same fingerprints. Why do we have fingerprints? Science really has no clear consensus and the three leading ideas are fingerprints increase tactile sensitivity, increasing gripping ability and one I find a bit strange is that they serve to prevent blister formation.

Since we did inherit them from our primate relatives, maybe we can get some hints from them. First thing we notice is that the blister idea is pretty useless for monkeys, chimpanzees and the rest of our primate relatives. That would leave the reason to be either an increase in tactile sensitivity or an increase in gripping ability. What do we know about fingerprints on primate other than ourselves? Well we notice that not only are they on the fingers of chimpanzees but they are on their toes also. Not only that but the prehensile tail of some monkeys have tail prints too. Seems the reason of them increasing tactile sensitivity is looking fairly dim. Actually it seems more like dark storm clouds are gathering over it. When was the last time you saw a monkey gently probing a surface with their prehensile tail? You do see them grasping objects with it, you also see some hanging from branches by it. We have all seen monkeys swing from branch to branch high above the ground with both their hands and feet. Any increase in gripping ability would certainly be an advantage that the genome would keep but it seems the genome would only program the ridges with one proviso and that is that none of the ridges are parallel to the direction of the finger. If they were, that would be a point where the grip would slip rather that be increased. One other thing that makes this a valid possibility is that there are Apocrine glands on your hands but an rarity of Sebaceous glands almost as if they were built for swinging from trees.

The second example I want to speak about is not as obvious as fingerprints but again it is mostly out of the control of our genome. Our vascular system. In particular I will look at the blood vessels of our retina which like fingerprints are unique. As with fingerprints, a retinal scan of genetically identical individuals is not the same. Why is this? De novo vasculogenesis form blood vessels from endothelial precursor cells [angioblasts] that differentiate into a vascular tree of blood vessels. Angiogenesis is a similar process and to put it simply instead of using angioblasts, new vessels are formed from preexisting ones. Ok, here is where it gets tricky to explain but I will give it the old college try so bear with me. The genome is unquestionably in full control of vasculogenesis. But as I wrote, vasculogenesis forms a vascular tree which needs to be pruned in some places and extended in others. This is where our friend angiogenesis comes in. There is also a third type of vascular growth called intussusception [that was hard to spell] that is also known as splitting angiogenesis but I will not talk about that here. Angiogenesis like vasculogenesis before it is in control of the genome and this is what prunes and extends the new vascular tree. Yet as seen above, a retinal scan of two genetically identical people is different which means the pattern of blood vessels is different, that is what I mean be saying it is mostly out of control of the genome. Since vasculogenesis is clearly under full control that means by a deduction worthy of Sherlock Holmes, angiogenesis isn’t [I can just imagine what my old cardiologist co-workers would say]. Yes I said it is in control of the genome and I will still say it is as far as it being active [just as growing ridges on our fingertips is controlled by the genome] and as far as being given ‘instruction’ how to prune or extend the vascular tree. As with fingerprints, the pattern is not determined by the genome. What controls it? As with fingerprints I can’t answer with any certainty and I doubt anyone could [or would be so arrogant as to try..well there was this one cardiologist I worked with that would try]. Unlike with fingerprints this doesn’t seem to be totally random. It seems that the vascular tree that is generated through vasculogenesis is pruned and extended on an as needed basis throughout the growing embryo since it is not ‘predetermined’ what shape and structure of the finished body and organs will be due to genetic mutations so the vascular system is “custom” fit for each of us. There is a rough ‘blueprint’ of the circulatory system in a human yet there are many variations. For the most part our circulatory systems [just speaking of the veins, arteries, blood vessels and capillaries] are similar yet there are variations. Not only are there variations from individual to individual, there are variations on each side of your body [just compare the backs of your hands or the pattern of veins on your wrists].

These are just two examples that stood out during my reading about the anatomical quirks of the human body. My reading actually made me learn more about the eye than I ever wanted to know. I will write in another article how badly ‘designed’ [if god is the designer, he needs to be fired] it really is along with a few other parts of the human body so we will come back to the circulatory system, you have been warned 🙂

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3 Responses

  1. Fascinating stuff! I have read that government officials used fingerprint impressions, in wax or clay, I suppose, to mark documents. If I remember it was 13th or 14th century. Amazing!

  2. Okay, that fingerprint thing is going to keep me awake.

    I agree that the blister possibility is null and void – I cant see how little ridges can reduce the effect of an impact or rubbing that causes blisters.

    For tactile, I guess we could do an experiment and sand them off – see if there’s a noticeable sensory difference. I understand that they don’t really grow back if you do that.

    For increasing friction for grasping, that sort of makes sense – except when you consider callouses. They rise up as hardened lumps (so much for tactile there too) and the grooves are lost.

  3. I watched a documentary a while back about a cop who’s trying to get using earprints on par with fingerprints

    on the idea that ears also have unique prints and criminals will often listen at a window or door – ear pressed to it – so it gives liftable prints.

    don’t know if that’s becoming accepted or not..

    nina
    http://ntrygg.wordpress.com

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