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Author Topic:   How does epigenetics influence evolution?
Delta-9
Junior Member (Idle past 5089 days)
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From: VA
Joined: 03-24-2010


Message 1 of 6 (555304)
04-13-2010 3:09 AM


Hi everyone, I have some question regarding epigenetics and evolution. I would greatly appreciate it if this was in the biological evolution forum, as I think it would fit.
First, how can epigenetic traits be passed on to subsequent offspring, as seen with changes in mouse hair color, when epigenetic changes don't effect the DNA sequence of the organism? Does it have to do with some retaining trait of the chromosomes during meiosis?
I also heard that most of the epigenetic information in sexual species is contained in the mother's DNA (so in the egg gamete?), is that why changes in diet while pregnant can change the offspring physically?
Next, why is it thought that epigenetic changes have a more profound impact on micro-organisms, particularly single celled organisms, than multi-cellular life?
Which brings me to the chief question, how big of a factor is epigenetics in regards to the evolution of life? If it is a big factor, would it contribute to punk eek in that populations would be able to physically change rapidly in response to environmental pressure without the need of a DNA mutation?
Thanks in advanced to all responses.

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 Message 3 by Blue Jay, posted 04-14-2010 10:30 AM Delta-9 has not replied
 Message 4 by Dr Jack, posted 04-14-2010 10:46 AM Delta-9 has not replied
 Message 5 by Wounded King, posted 04-14-2010 11:14 AM Delta-9 has not replied

  
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Message 2 of 6 (555572)
04-14-2010 8:52 AM


Thread Copied from Proposed New Topics Forum
Thread copied here from the How does epigenetics influence evolution? thread in the Proposed New Topics forum.

  
Blue Jay
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Message 3 of 6 (555590)
04-14-2010 10:30 AM
Reply to: Message 1 by Delta-9
04-13-2010 3:09 AM


Hi, Delta-9.
Welcome to EvC!
Delta-9 writes:
First, how can epigenetic traits be passed on to subsequent offspring, as seen with changes in mouse hair color, when epigenetic changes don't effect the DNA sequence of the organism? Does it have to do with some retaining trait of the chromosomes during meiosis?
I'm not a molecular biologist or geneticist, but I have taken the relevant coursework. Let me give you a few simple answers, and maybe an actual molecular geneticist (such as Wounded King) can provide you with something better.
For the lurkers, epigenetics refers to inherited traits that are not encoded in nucleotide sequences. Usually, it has to do with patterns of gene expression perpetuating after cellular division: expression of genes can be promoted or inhibited by certain proteins and other molecules in a cell. Some genes can be inhibited, and some can be promoted: differences in the patterns of inhibition and promotion can cause cells with identical genotypes to develop in different ways.
And, when a cell divides, its patterns of inhibition and promotion are often transmitted to both daughter cells. So, cells (including embryos) can inherit the expression patterns, and the resulting developmental traits, of their progenitors.

-Bluejay (a.k.a. Mantis, Thylacosmilus)
Darwin loves you.

This message is a reply to:
 Message 1 by Delta-9, posted 04-13-2010 3:09 AM Delta-9 has not replied

  
Dr Jack
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Message 4 of 6 (555592)
04-14-2010 10:46 AM
Reply to: Message 1 by Delta-9
04-13-2010 3:09 AM


Which brings me to the chief question, how big of a factor is epigenetics in regards to the evolution of life? If it is a big factor, would it contribute to punk eek in that populations would be able to physically change rapidly in response to environmental pressure without the need of a DNA mutation?
No.
Epigenetic changes done add to each other; they only act once. This means that, unlike mutations, lots of epigenetic changes don't add up into big phenotypic changes. Remember, as well, that epigenetics aren't a seperate thing to genetics; epigenetic changes are possible only where the genes allow.
(Oh, and Punk Eek is mostly wrong, anyway)
Edited by Mr Jack, : Must slag off punk eek

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 Message 1 by Delta-9, posted 04-13-2010 3:09 AM Delta-9 has not replied

  
Wounded King
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From: Cincinnati, Ohio, USA
Joined: 04-09-2003


(1)
Message 5 of 6 (555594)
04-14-2010 11:14 AM
Reply to: Message 1 by Delta-9
04-13-2010 3:09 AM


First, how can epigenetic traits be passed on to subsequent offspring, as seen with changes in mouse hair color, when epigenetic changes don't effect the DNA sequence of the organism? Does it have to do with some retaining trait of the chromosomes during meiosis?
The answer is probably yes, depending on what you consider to be a 'trait of the chromosomes'. In the case of the mouse agouti example it is a question of methylation state of cytosine residues in a transposable element (IAP) which is upstream of the Agouti gene and creates the Agouti Viable yellow allele.
So while the phenotpyic variation associated with the Agouti Viable yellow allele is the result of epigenetic changes the allele itself is a traditional DNA based variant.
The methylation state of the IAP element is the basis of the variation, when the IAPs cytosine residues are highly methylated it its transcription driving activity is silenced, when unmethylated and active it serves to drive ectopic expression of the Agouti gene, this is called the pseudoagouti phenotype.
When pregnant Agouti Viable yellow mothers are fed methyl donors in their diet their offspring will tend towards a higher proportion of pseudoagouti phenotypes, this occurs over a large span of development, it is not neccessary to target the zygote and it certainly isn't a case of an effect from the gamete's, although the next generations gametes will be affected by their in utero exposure (Cropley et al., 2006; Cropley et al., 2010)
I also heard that most of the epigenetic information in sexual species is contained in the mother's DNA (so in the egg gamete?), is that why changes in diet while pregnant can change the offspring physically?
There are a couple of things here, one is that the difference in epigenetic marks between maternal and paternal genome complements is part of another phenomenon called imprinting which is somewhat distinct from what is happening with the Agouti Viable yellow mice. The other is that dietary changes can readily affect phenotype without any sort of epigenetic mechanism, i.e. a lack of folic acid can lead to spina bifida.
Next, why is it thought that epigenetic changes have a more profound impact on micro-organisms, particularly single celled organisms, than multi-cellular life?
The main reason is that when a bacterial cell replicates then the epigenetic state of the daughter cells is much more closely linked than in the case of a multicellular organism which will have a wide variety of epigenetic states amongst the cells making up the organism. So epigenetic state inheritance in bacteria is much more direct. In many ways the equivalent thing to look at would be the epigenetic changes between different cell lineages within a developing multicellular organism rather than between multicellular parent and offspring organisms.
This means that in evolutionary terms epigenetic inheritance is liable to play a much greater role in bacterial than multicellular populations.
In terms of multicellular/metazoan populations it isn't clear yet what if any role epignetic inheritance such as in the Agouti Viable yellow case is, the effects are very transient so there is no stable inheritance, but the existence of that allele at all gives rise to a wider spectrum of colour variation in a population that is genetically identical, which might have evolutionary consequences.
Imprinting has much better claim for an important role in evolution, particularly in the interactions between male and female parents. One of the major factors in imprinting is what is called parental conflict, where fathers want their offspring to gain as much of the mothers resources/nutrients as possible while mothers want to limit their expenditure to increase their future breeding potential (Moore and Reik, 1996). So at least in mammals imprinting forms an important part of an arms race between the sexes.
I very much doubt any of these things have anything to do with punk eek.
TTFN,
WK

This message is a reply to:
 Message 1 by Delta-9, posted 04-13-2010 3:09 AM Delta-9 has not replied

  
Delta-9
Junior Member (Idle past 5089 days)
Posts: 2
From: VA
Joined: 03-24-2010


Message 6 of 6 (555605)
04-14-2010 1:08 PM


Thanks for the replies so far. I'm short on time (studying for a big test I have to take later today), so I can't reply to anything specifically now. But I'll definitely read and respond either tonight or tomorrow.

  
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