Free This Is Your Brain on Sex by Kayt Sukel Page B

expressed genes encourage the growth of offspring, the maternally expressed genes help keep growth to a manageable size. He calls this theory the “conflict hypothesis,” and some scientific work in animal models lends credence to the idea. “Genes of paternal origin make offspring grow larger and demand more resources from the mother,” Haig told me. “But the maternally expressed genes show preferenceto the mother’s ability to reproduce in the future and help limit any one offspring from taking too much.”
    Why did I lead you down this particular garden path? There has been no evidence that the baby or his parents did anything to change gene expression, and no evidence of life experiences adding methyl groups or throwing kinks into microRNAs with genomic imprinting. But this is a basic epigenetic result that can have profound impact on behavior. What’s more, it is an effect that is passed from one generation to the next. Without even taking a bite of cheeseburger, my parents were giving me an epigenome that made alterations to the way my genes expressed themselves and my subsequent behaviors through some of these imprinted genes. Because not only do they affect growth; imprinted genes also have a lot to say about brain development and function. “When scientists have genetically manipulated imprinted genes, the most frequent effect identified relates to embryonic growth,” said Dulac. “But the second most frequent phenotype identified involves cognitive function.”
    In two papers published in an August 2010 issue of Science magazine, Dulac, Haig, and their colleagues reported their finding of differential expression of parent-of-origin genes in the mouse brain. They found 347 genes with sex-specific imprinting features that influenced the development of different areas of the cortex and, interestingly enough, that randy-dandy hypothalamus. 2 These findings suggest that imprinted genes are involved in feeding, mating, and social behaviors—like our old friends, sex and love.
    Imprinting is not just a simple, static change made in the womb. No, these imprinted genes turn on and off over time, regulating the expression of genes at different points in the life span. What’s more, maternally expressed genes contribute most to the developing brain, while paternally expressed genes seem to do more work once the brain reaches adulthood. Why, exactly, is unknown. 3 “[Genomic imprinting] is a dynamic process,” said Dulac. “It’s not something fixed through the life of the organism. The neurons and neuronal precursors have a certain repertoire during development where maternal or paternal genes are preferentially expressed. Later in life, that pattern of expression is different. It’s a major mode of epigenetic regulation and a gold mine for the future understanding of howour genes may control our behaviors.”
    As I said, it is all my mother’s fault. It is possible that various traits and aspects of my behavior, including those involved in love and sex, can be traced back in part to the expression of Mom’s imprinted genes. But if I am to give credit where it is due, apparently my father had quite an influence. So I will let him share some of the blame too.
    What about Those Cheeseburgers?
    I can guess what you’re thinking: “Genomic imprinting is interesting and all, but can you really say it’s your mother’s or father’s fault? And what does that have to do with cheeseburgers, for that matter? Or love?” You are right. There I go talking about genes as if they are little General Pattons directing the troops. It’s a hard habit to break. But imprinting is important. It shows you how epigenetics can change the way your genome works before you even make the jump from embryo to fetus, not to mention from early childhood to adulthood. But the cheeseburgers may play a role too, if agouti mice have anything to say about it.
    Agouti mice are a strain of laboratory mice often used as a model to study