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150 MYA Genomic Imprints
Imprinted genes: the "same" gene can have effects that differ according to whether you got it from mom or from dad. There are, I believe, about 100 identified imprinted genes (Jirtle RL & Weidman JR (2007) Imprinted and More Equal. Am Sci, 95:143-149. http://www.geneimprint.com/media/pdf...4_fulltext.pdf).
The male imprints lead to larger placentas, larger fetuses, greater monopoly of maternal blood and sugar supplies, greater amounts of dental enamel, greater deposits (sometimes) of brown fats, and a larger hypothalamus but a smaller neocortex. They also enhance nesting, nursing, and pup retrieval (Burt & Trivers, 2006, chapt 4). Female imprints have the opposite effects. Why? David Haig and his fans support the notion that male patterns have to do with selfishness, discovery, and resource expenditure. Female imprints conserve her assets for her next offspring, rather than the current one. They also tend, in some studies, to show up in a larger neocortex!(Bob Trivers has suggested that the right cortex and left may reflect different genomic investments.) If imprints respond to environments, then we have a mechanism that mediates K- and r-selection effects and the availability of "estrogenized" males in stable environments and of nasty raptor-types when food, mates, and invasions are on today's menu. See my thoughts on males and females in my review of Kathleen Parker's book, Saving the Males... JimB "Evolutionary Origin Of Mammalian Gene Regulation Is Over 150 Million Years Old "ScienceDaily (July 3, 2008) — "Scientists at the Babraham Institute, the Sanger Institute, the University of Cambridge and the University of Melbourne and the University of Texas at San Antonio (all part of the SAVOIR consortium) have found that a complex, highly conserved and extremely important mechanism of controlling genes is over 150 million years old... We all get two copies of every gene, one from our mother and one from our father. In many cases both copies are used or 'expressed', however it is becoming clear that for some genes either the mother's or the father's version is used preferentially, a phenomenon known as genomic imprinting. Specific chemical modifications to the DNA, such as methylation, appear to give the chromosomes a 'memory' as to their parental origin... "These 'epigenetic' imprints, from the Greek meaning 'on top of', modify the structure of the DNA but not its sequence. In addition to parental modifications, it is thought that epigenetic changes may also arise in response to environmental factors, enabling an organism's genes to adapt and respond differently, even though the gene sequence does not change." More at: http://www.sciencedaily.com/releases...0701140658.htm Also at: http://www.babraham.ac.uk/news2008/jun-29.html Original paper http://www.nature.com/ng/journal/vao...bs/ng.168.html |
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