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Thread: Genetics: Blond hair as kids gradually becomes dark hair as adults. Why?

  1. #1 Genetics: Blond hair as kids gradually becomes dark hair as adults. Why? 
    Forum Cosmic Wizard icewendigo's Avatar
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    I know a many people that had really blond hair when they were kids, and their hair gradually became darker through the years until they reached adulthood where their hair was dark brown.

    Arent you supposed to have either blond hair genes or dark brown genes (or blond hair that is rececive? Its almost like the blond genes start out as not that recessive and gradually become dominated by the brown genes, or what?)? Why does it start out blond and gradually becomes dark?


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    Forum Radioactive Isotope cosmictraveler's Avatar
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    I was born a blond and to this day, very long time now, I still retain blond hair and if I should stay in the sun for awhile for a few days it actually becomes more blonder. It seems like the less sun I get it is getting white but going out and about turns it blond was again.


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    Quote Originally Posted by icewendigo View Post
    I know a many people that had really blond hair when they were kids, and their hair gradually became darker through the years until they reached adulthood where their hair was dark brown.
    isn't it the same for eyes - if i remember correctly all babies of caucasian extraction are born with blue eyes
    only later do some of them change their eye colour to brown or green

    it's almost as if a delayed epigenetic program kicks in at some point where the initial blue eyes / blond hair combination turns to a different colour
    why, i have no idea
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    People have a different response to UVR exposure as well as different base status. So two babies might be (genetically based) blonde as a base state but have different (genetically based) responses to UVR over time, hence some will darken and some won’t.

    How is epigenetics relevant?
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    because what a person looks like doesn't just depend on their genes, but how and when those genes get switched on and off
    e.g. all babies can digest milk, but most human beings lose the capability to digest it when they're a few years old and become lactose intolerant
    some pastoral races have a lucky disposition where the capability doesn't get lost, which is purely down to keeping an active gene for lactose digestion rather than seeing it switched off
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    Epigenetics could be relevant because hair darkening is often be associated with puberty, and puberty itself probably has some degree of epigenetic control to it - perhaps in the regulation of hormones and their receptors.

    Up until age 11/12 I had brown hair. I now have black hair.
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    My hair is getting lighter.
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    I started out with platinum blonde hair and now its a dark ash blonde... well when I don't have it bleached or dyed. I was always told as a kid that color treating your hair will make your natural color darken, just like shaving the hair on my legs caused what used to be fine blonde hair to turn into coarse black stubble. Now I realize most of that was old wive's tales but I never had a legitimate explanation to replace the myths.
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    The blond at birth with hair darkening in adulthood is a genetic pattern common to the racial group from middle Europe, Southern Germany, Switzerland, northern France etc. It is just the pattern they have. It usually goes with a mezo morphic body type, fair skin, and blue to grey eyes.
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    Quote Originally Posted by marnixR View Post
    because what a person looks like doesn't just depend on their genes, but how and when those genes get switched on and off
    hence why I talked about UVR exposure.

    This may be a terminology thing. When you said ‘epigenetic’ I thought you meant the inherited alteration of gene expression (i.e. Lamarckism). If you simply meant that your environment effects your gene expression, then of course, and the sky is blue. Did you mean something else?

    Re lactase persistence, my understanding was that it developed in groups who undertook animal husbandry / domestication etc (i.e. kept animals and drank their milk), and that this was a selection pressure (i.e. the people who produced lactase for longer were at an advantage and so over generations average persistence of lactase expression lengthened)
    Is it a ‘lucky disposition’ or is it natural selection which has little to do with luck.
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    Quote Originally Posted by SHF View Post
    This may be a terminology thing. When you said ‘epigenetic’ I thought you meant the inherited alteration of gene expression (i.e. Lamarckism). If you simply meant that your environment effects your gene expression, then of course, and the sky is blue. Did you mean something else?
    i meant that certain genes are dormant until switched on, either through an external or an internal stimulus
    someone else mentioned puberty, which is another epigenetic event : the genetic disposition is always there, but it only kicks in depending on hormonal triggers

    nothing to do with lamarckism which refers to inheritance of acquired characteristics - epigenetics is the modification of the phenotype for a given genotype, depending on the timing in the activation of those genes
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    hhhmmm…

    well good old wiki says “In biology, and specifically genetics, epigenetics is the study of heritable changes in gene expression or cellular phenotype, caused by mechanisms other than changes in the underlying DNAsequence” (Epigenetics - Wikipedia, the free encyclopedia)

    perhaps you mean ‘epigenesis’ ? “the unfolding development in an organism, and in particular the development of a plant or animal from an egg or spore through a sequence of steps in which cells differentiate and organs form” (http://en.wikipedia.org/wiki/Epigenesis_(biology))

    or perhaps ‘epigenetic theory’? “Epigenetic theory is an emergent theory of development that includes both the genetic origins of behavior and the direct influence that environmental forces have, over time, on the expression of those genes. The theory focuses on the dynamic interaction between these two influences during development.” (Epigenetic theory - Wikipedia, the free encyclopedia)

    I really don’t get what is special about turning on and off genes enough to call it an ‘epigenetic program’ rather than just a ‘genetic program’. Surely all expression is an epigenetic programme in your sense of it? and so the term is pointless, no? You say puberty is an epigenetic event, what isn’t? why isn’t it just a genetic event? (given that, as anyone who has glanced at popular genetics books knows, your genes are not a blue print but a recipe, blah blah blah).

    I’m posing a real question, not being flippant, what is this ‘epigenetics’ thing really? seems rather overstated to me. The genes in each of your cells are constantly being upregulated/downregulated, is all that epigenetics? to me it's just genetics.
    Last edited by SHF; January 30th, 2013 at 03:14 PM. Reason: typo
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    The problem is that there are multiple meanings to the term epigenetics; worse still, it means different things in different contexts. Even worse, it's misused all over the place and is often touted as a the next great paradigm shifter. Back on the ground, it is typically used today - and quite differently from its original usage - to refer to a type of gene regulation that is heritable (that's the important part) that does not directly involve changes at the sequence level of DNA. In other words, phenotype is being inherited in a manner that is not directly dependent on the sequence of DNA inherited. Specifically, it's referring to the methylation of DNA bases and the acetylation of the DNA-binding proteins known as histones. The epigenetic machinery itself is ultimately "encoded" at the sequence level, however.

    This sort of regulation is quite different to that which occurs when a transcription factor binds a promoter sequence.

    Epigentics is a form a gene regulation, as you say. The difference is that this type of regulation produces a high degree of cross-generational stability in a lineage of cells, so that, for example, kidney cells will always be kidney cells and never develop into liver cells; that is, epigenetics mechanisms can define profiles of gene expression.






    It was I that suggested puberty may have an element of epigenetic control to it. I've no idea if it does or not, to be honest. Seemed like a reasonable suggestion at the time though. Or perhaps I was just defending marnixR?
    Last edited by Zwirko; January 30th, 2013 at 05:11 PM.
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    Hi Zwirko,

    Still doesn’t seem clear. Yes, certainly people bandy the term around without really thinking about it resulting in collective confusion as to who is trying to say what.

    Can you give me one definitive example of something that is epigenetic and something that is not?

    Why would puberty be a good shout?

    Zwirko is defining epigentics as ‘ a type of gene regulation that is heritable…that does not directly involve changes at the sequence level of DNA.’

    Marinx is defining epigenetics differently as ‘the modification of the phenotype for a given genotype, depending on the timing in the activation of those genes’

    If marinx could supply a source for such a definition of epigenetics that would be useful. My understanding is the same as Zwirko’s in that epigenetics = heritable changes independent of DNA sequence, although I’m not sure why Zwirko (in post #6) didn’t bring this up regarding Marinx’s first sentence of post #5 which intimates epigenetics being just the turning of genes on and off.

    Also (marinx) I don’t know what you’re talking about re all Caucasian babies having blue eyes initially???
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    Brassica oleracea Strange's Avatar
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    As far as I know, both definitions are correct.

    This site has some good information on epigenetics including a section on inheritance (with some examples): Epigenetics

    I have seen some reports of studies that showed that environmental factors (malnutrition) could affect the second generation. I don't know if that has been confirmed. It sounds kinda dubious...
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    Gene regulation can be brought about by a wide variety of mechanisms, epigenetics is just another form of gene regulation. Mechanisms that are not epigenetic in nature would be most examples you can think of, such as those mediated by transcriptional repressors, enhancers, insulators, elongation factors, RNA processing and degradation, RNA interference, and regulation of translation. Generally speaking, these sorts of mechanisms are dependent upon the diffusion of molecules and thus it would be difficult for a eukaryotic cell to pass on its regulatory state to a daughter cell in a consistent and reliable manner, particularly so when the organism needs to have well-defined and stable cell and tissue types. Epigenetics offers a solution to that problem; in this regard it is sometimes referred to as "molecular/cellular memory".


    The best example of a process that is epigenetic is female X-chromosome inactivation in eutherian mammals. The inactivation is very stable and passed through many, many cell divisions.


    A quick google scholar search tells me that experimental alteration of epigenetic marks that are thought to be involved in the onset of puberty in the mouse have been observed to result in so-called pubertal failure. So epigenetics may have a role in puberty, after all. Phew!
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    I have a question regarding balding genes:

    My high school biology teacher said that the balding gene comes mostly from your maternal grandfather (so if he has a receding hair line, you will likely will also). This sounds like bull puckey. Does anyone know if this is true?
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    Thanks for the link.

    Quote Originally Posted by Strange View Post
    As far as I know, both definitions are correct.
    Really? The second definition? let’s say the definition applies to epigenetics, doesn’t it also apply to things other than epigenetics (like the action of transcription factors)?

    According to the first video in the link, epigenetics is the addition/subtraction of chemical tags to histones and the DNA (though not the bases), thus affecting the coiling/wrapping. If epigenetics is about whether or not the DNA is accessible (e.g. to transcription factors) then surely all gene expression is regulated partly by epigenetic means? (either a gene is accessible or not, and this depends on its epigenetic regulation)

    Regarding balding, I have heard that also. Looks like maternal and paternal influence is important though:

    “Recent research confirmed the X-linked androgen receptor as the most important gene, with a gene on chromosome 20 being the second most important determinant gene (snpedia). This research suggests that heredity of AGA is X-linked; however, research has also shown that a person with a balding father has a significantly greater chance of experiencing hair loss. Men whose fathers had experienced hair loss were 2.5 times more likely to experience hair loss themselves, regardless of the mother's side of the family, which may suggest Y-linked heredity plays a role.”
    (Baldness - Wikipedia, the free encyclopedia)
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    also, Zwriko, was it this paper (http://www.nature.com/neuro/journal/...l/nn.3319.html) you were referring to? was an interesting read if so (and also if not)
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    I think it was a 2010 paper I had in mind, can't recall the details. The one you linked to looks to be along similar lines though.


    I think that if epigenetics does play a role in puberty it's not really the direct cause of hair darkening, at least not the best way to answer the question. For that we'd probably be better off looking at the hormones of puberty and how they affect melanin production, and also consider how melanin levels change by other means during development.
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    when I was about 7 8 years old I had gold hair color slightly after puberty it turned to black... I have seen to most people that their hair darkens with time but to me it extremely change... what is the specifiec reason for this naturaly darken? I know it is probably due to genes and hormones... but does it have any reason? why it happens???
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    I had blond hairs, they became black when i was 7
    I can't speak english.
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    My hair was quite light when I was little, now it's a dark brown colour... apart from about half a dozen hairs that are grey.
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    It's certainly genetic. My sister and I were both almost white haired blonde when we were little. It started to darken when we were in early primary school. We finished up with hers a very, very dark brown, mine was more of a light, mid-brown with red highlights - which lasted until I got a few grey hairs, before I'd left school. Unfortunately I never developed that beautiful all white hair you see on some people in their thirties and forties. Most of our second cousins (no first cousins on that side of the family) showed the same colour progression with their hair.

    However, my own children were completely different from each other. One was born with that dead black hair some newborns have. Which fairly promptly fell out and was replaced by ... completely black hair. The other child's hair was just like mine. Neither of them have acquired any grey. My husband didn't have any grey hair at all until a few years ago and even now it's not really visible, nor is he bald though he's started to recede a bit at the front the last five years or so. Though his beard is now fairly white around the mouth and chin. So it looks as though each daughter's taken on a different side of the family.

    I'd always attributed our blonde-brown-white progression to the red-haired element in our backgrounds. My great grandmother had red hair which went completely white. She married a Swedish man who probably reinforced the blond tendencies. My grandmother and 2 of her sisters didn't have red hair but they were completely white by the time they were in their fifties, and my mother's much the same.
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    well what I was thinking to say is... we get older our hair gets darker... thus dark hair= grown ups... can it be that biologically chemically people with darker hair are "older"
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    Hardly. My husband and our older daughter have different colouring from me and our younger daughter. Buuuut ... both children are very much more like him in physique and facial structure - though one's been unfortunate enough to inherit my neurological disorder which means her feet and ankles are weak and oddly shaped. Their eye colours are completely different - the black haired one has darkish smoky blue eyes, the other has fair average quality hazel eyes like both of us.

    Babies may be born bald or with copious quantities of hair which falls out. Most toddler's hair is finer than adult hair regardless of colouring. It's pretty hard to tell which was which once those children become teenagers or adults. Nor can you predict which will go grey or bald or both from how hair colouring develops through puberty to maturity.

    As for darker hair indicating "older". My personal experience is that having a partner who maintains a dark hair colour while I went more and more grey (dyed blonde nowadays of course) makes it seem the other way around.
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  28. #27  
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    Hair texture can also change at puberty.
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    I dunno if this is helpful, but.. can we say there is a normal/optimal hair colour for mammals? Then brown hair - for example - would not require explanation, but any deviation from (brown?) must be caused by conditions unique to the species. So, the polar bear would be brown, but for the greater advantage of camouflage; the skunk would be brown but for the greater advantage of announcing what it is.

    The social importance of grooming - I think - mostly explains human head hair. Shifting grooming attention to the head compliments face-to-face communication. So we aren't communicating with our backsides like gorillas. I don't see how hair colour is relevant here though.

    There might be some advantage against host-specific parasites, like lice, when hair colour changes throughout life. However (modern) human head lice are dandruff-coloured so they're pretty well camouflaged in any population or agegroup. Add the complication that individuals in sore need of grooming are going to enjoy more intimate contact and therefore reproductive success... *shakes head, walks away*.
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    I had almost white hair when I was around 10 years old, it changed to blond and my hair now (29 years old) is dark blond. When Im 90 hopefully it will go back to being white.
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    Hi guys,felt compelled to comment on this thread. I was born with black hair, after a few weeks it all fell out and grew back in practically white, gradually getting darker. Now at age 29 its light to medium brown.
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    Quote Originally Posted by Harold14370 View Post
    My hair is getting lighter.
    in thickness or in color? *ducking*
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    I was born with jet black hair......which was replaced with what my mother called "Bella" hair..(towhead) ..very very very blonde hair. I was blonde till I turned 19 then my hair turned more chestnut, then redder, then after my kids very very dark....but it lightens in the sun...
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    it looks it gets more and more interesting... for something simple as hair...
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    Quote Originally Posted by blackscorp View Post
    it looks it gets more and more interesting... for something simple as hair...
    *chuckle*who'd a thought!
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    Think it might be as simple as an adaptation to receive more UV and ability to produce more vitamin D, and thus use calcium better to grow stronger bones while young.

    As long as the hair turns dark before puberty there's little risk or strong negative selective pressure from folic acid crash and new born spinabifida.
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    I think that blond hair, certainly in females, is seen as a 'marker' of youth and fecundity in some societies?

    Grey or white hair; I always understood to be due to gradual increase of air being incorporated into the hair strand, which then reflects more light and therefore appears white/grey. Anybody know if this is right?


    OB
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    Quote Originally Posted by One beer View Post
    I think that blond hair, certainly in females, is seen as a 'marker' of youth and fecundity in some societies?

    Grey or white hair; I always understood to be due to gradual increase of air being incorporated into the hair strand, which then reflects more light and therefore appears white/grey. Anybody know if this is right?


    OB
    I don't but I'll ask my salon person........if I remember....while she's now covering the small amount of grey I have....we don't go grey much in my family till 70....but I'm gonna take ALL precautions!! We gingers, fade! *sigh*
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    Quote Originally Posted by Zwirko View Post
    Gene regulation can be brought about by a wide variety of mechanisms, epigenetics is just another form of gene regulation. Mechanisms that are not epigenetic in nature would be most examples you can think of, such as those mediated by transcriptional repressors, enhancers, insulators, elongation factors, RNA processing and degradation, RNA interference, and regulation of translation. Generally speaking, these sorts of mechanisms are dependent upon the diffusion of molecules and thus it would be difficult for a eukaryotic cell to pass on its regulatory state to a daughter cell in a consistent and reliable manner, particularly so when the organism needs to have well-defined and stable cell and tissue types. Epigenetics offers a solution to that problem; in this regard it is sometimes referred to as "molecular/cellular memory".
    A good example of epigenetics in play with hair colour in mice is seen with studies on the Agouti gene described by Nessa Carey in her book "The Epigenetics Revolution'...........now I try to avoid the hype with this title, however it is still very interesting. Note that the following does not deal with changing hair colour of mice during a single generation yet processes of epigenetics certainly can impact on gene expression during a single generation as evidenced during ontogeny and suggested with diabetes and significant stressful environmental impacts on somatic DNA. Actually recent work undertaken to assess environmental stresses on gene function of mice is referred to here.

    The Agouti gene is phenotypically expressed when turned on with a hair follicle which is banded in colour with a black tip, yellow middle and black base giving a mouse its normal 'mousy brown colour'. Work done by Emma Whitelaw on a set of genetically identical mice revealed interesting results. Genetiticists are aware that if the Agouti gene is switched off, then the mouse hair is completely black (called "A") . There is another variant of the agouti gene (called agouti viable yellow or Avy) where the agouti gene is switched on permanently and the hair is yellow along its entire length. For the normal mouse with the 'normal agouti gene' the banded appearance is attributed to whether the agouti gene is switched on or off during the follicles growth cycle. For the yellow mouse the agouti gene is switched on continuously and the entire follicle is yellow. For the black mouse, the agouti gene is inactive over the entire follicle growth cycle.

    Of course mice have two copies on the agouti gene inherited from the mother and father. The Agouti viable yellow gene Avy is dominant to the "A" version. All pretty straight forward so far. Since all the mice in the the sample population were genetically identical it would be expected that they would all look the same, but they didn't. It was found that when a piece of DNA called a retrotransposon was inserted just before the agouti gene, it keeps the agouti gene switched on continuously.

    Now comes the important epigenetic bit......if the retrotransposon becomes heavily methylated then the retrotransposon cannot keep the agouti gene switched on hence the banded colour of normal mice. When the retrotransposon was unmethylated it turned on the agouti gene continuously resulting in yellow mice.

    Now despite genetically identical populations, yellow mothers tended to have yellow offspring and banded mothers tended to have banded offspring etc. This was attributed to the degree of methylation on the retrotransposon carried in the mothers egg. This methylation was not wiped clean on the creation of the new generation.


    .....anyway thought this may be of interest even given the fact that it appears the agouti gene is not present in humans. :-))
    Last edited by Implicate Order; October 19th, 2013 at 10:49 PM.
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