July 28, 2009
Parental Genes Fight For Control During Development
Pat Benatar was more right than we knew. Love is a battlefield.
CAMBRIDGE, Mass., July 28, 2009 -- An analysis of rare genetic disorders in which children lack some genes from one parent suggests that maternal and paternal genes engage in a subtle tug-of-war well into childhood, and possibly as late as the onset of puberty.
This striking new variety of intra-family conflict, described this week in the Proceedings of the National Academy of Sciences, is the latest wrinkle in the two-decades-old theory known as genomic imprinting, which holds that each parent contributes genes that seek to nudge his or her children's development in a direction most favorable, and least costly, to that parent.
"Compared to other primates, human babies are weaned quite early, yet take a very long time to reach full nutritional independence and sexual maturity," says author David Haig, George Putnam Professor of Organismic and Evolutionary Biology in Harvard University's Faculty of Arts and Sciences. "Human mothers are also unusual among primates in that they often care for more than one child at a time. Evidence from disorders of genomic imprinting suggests that maternal and paternal genes may skirmish over the pace of human development."
So our genes are fighting it out. Will mom or dad's genes rule the liver? Whose genes will capture the high ground of the brain? Will the loser at least manage to hold onto the colon or kidneys?
I don't get how this works. Is the same gene (allele or whatever) behaving differently depending on whether it comes from the mother or the father? Is there an example of that? Doesn't the gene's interest lie in the reproductive success of the current host? Why does the gene care about mom or pop?
I agree - this sounds somewhat non-sensical - although it does make some sense from the pov of the child - i.e. overburdening the mother may lead to a failure to properly raise the child adversely affecting the child.
The only way I can see this working is as epigenetic affect on the expression of a gene and not directly as an effect of the gene itself.
And in women where one chromosome is randomly inactivated - couldn't chance play a greater role than some theoretical epigenetic gender struggle?
I think this theory is highly flawed - unless it is simply just saying the maternal and paternal genes have significantly different epigenetic influences - which I admit is somewhat interesting...
As far as a real "struggle" for dominance - I fail to see the pathway for such an actual conflict between the chromosomes...
(unless we are simply discussing the more abstract evolutionary struggle for dominance)
I'm not a biologist, but I've read about the phenomenon before. The example I recall is how astonishingly different ligers and tigons are from each other.
First off, why would evolution create an outcome where maternal and paternal genes have different interests? Mom can't have as many kids as dad can. Dad can knock up 5 women at the same time. He's not guaranteed that the woman who gave birth to one of his kids will also only get pregnant by him. Women invest more in their offspring than men do.
For a given woman that a guy knocks up he's best off having her invest more resources in the kid. The woman is better off investing less resources per kid and having more kids. Therefore the dad's genes will tend to encourage growth to a larger size while the woman's genes (or her epigenetic state on the chromosomes from her) will tend to restrain development.
Yes I think you present a very good case for the potential origins of these evolutionary traits.
However, and correct me if I missed it - but did they say what gender is more affected by this epigenetic competition?
Is there more of a prominent effect seen in female children due to random chromosome inactivation?
It seems to me there would be a more subtle affect on male phenotypes...
It is also interesting that such an evolutionary strategy could be coutner productive in modern monogamous relationships... (at least for males)
I wonder if selective pressure will moderate this epigenetic struggle going forward - or if neutral gene drift is too magnified due to our modern jet set society.
Perhaps we will not see real selective pressure again until physical isolation of space faring groups occurs...
(of course, by then, advances in genetic therapy/programing will far outweigh any environmental pressures)
There is a huge, huge, HUGE literature on genomic imprinting, a well-established phenomenon in which one of a pair of genes is silenced depending on whether it came from Ma or Pa. No point in arguing it doesn't happen; a zillion scientists say it does and have shown how. Start with Wikipedia and go on from there.
There is nearly as huge a literature on the conflict hypothesis about how a decision gets made whether to silence Ma's gene or Pa's. That's still a hypothesis--i.e., it's not yet engraved in tablets of stone--but there's a good deal of evidence for it. Plenty to read on that too, although some involves molecular and cell biology.
Ahh - so there is - good of you to point this out then!
(man I do love wikipedia!)
Then I would suggest the relevance of this latest study is how late in the process this genomic imprinting still seems to be having an affect on the development of the child.
To me it seems the Conflict Hypothesis, however, still has a fair ways to go before it can be called the winner - but it's my personal favorite!
I have an big issue with how these claims have been anthropomorphized and the suggestion that there is anything anyone can do about it. Some genes dominate, but at a biological/chemical level. That is known (though how may not be.) Look at families and you can often see quite dominant traits going back generations on one side or the other or even both.