Free This Is Your Brain on Sex by Kayt Sukel

partnership is seamless. You do not think about your software being the program and your hardware running it. You don’t have to. You are simply using your computer. It is only when one of the two breaks, making it impossible for you to beat that stupid game that has been invading your dreams, that their separateness becomes apparent.
    It is not so different in the field of epigenetics. “The genome is comparable to hardware. And the epigenome to the software,” says Randy Jirtle, director of the Epigenetics and Imprinting Laboratory at Duke University. “It’s a good analogy for understanding how it works.”
    Simply stated, epigenetics is the way that life experiences, your parents’ or your own, can actually mark up your DNA. By leaving the biological equivalent of highlights, ticks, and margin notes on individual and group genes, epigenetics can change their expression. In fact those epigenetic changes can alter whether those genes are expressed at all—even for several generations. I think it is fair to say that some of these marks are made in pencil, easily erased by new experiences or direct treatment, while others remain present in a most durable ink, holding steadfast as those genes are passed down to subsequent generations of offspring.
    If you have some recall of youreighth-grade science class, you remember that DNA is a double helix, two polymer chains of simple nucleotides called adenine, cytosine, guanine, and thymine twisted together into base pairs. This particular molecular architecture provides the genetic code, the blueprint that will direct the construction and function of every cell in your body. But it does not act in isolation. Researchers have now discovered several ways different proteins can chemically adhere to DNA, or its messenger pal, ribonucleic acid (RNA), to alter not the genetic material itself but rather how that DNA is used by the cells to make all those different critical proteins.
    The first and most stable of these molecular mechanisms is DNA methylation. Your experience in utero and in early life can result in an enzyme called DNA methyltransferase adding new molecules to the cytosine nucleotides in your DNA chain. This chemical change does not mutate the DNA itself. No, your genetic code remains fully intact, the order of nucleotides unchanged. Instead the methylation process adds a checkmark of sorts next to the genes it affects, typically resulting in the suppression or all-out removal of gene expression for the associated protein.
    A second epigenetic phenomenon involves histone proteins and increased gene expression. In the cell DNA is wrapped around a core of alkaline proteins called histones, which have long tails that sometimes manage to stick out of their double-helix enclosure. In a process called acetylation, a different type of molecule, an acetyl group, attaches to that errant tail and creates more space between the proteins and the DNA. By doing so, it leads to a surge in gene expression. Similarly, deacetylation can occur here too. As you have likely guessed, an experience may start a chemical chain that ultimately releases an enzyme called histone deacetylase, removing those acetyl groups (and with them the space between the DNA and histone proteins), resulting in fewer proteins being made.
    There is a third molecular mechanism studied in the epigenetics of behavior, one that involves microRNA. Back to eighth-grade science class: you probably have a vague recollection that messenger RNAs copy the genetic code from DNA and then travel into the cell nucleus so it can make the prescribed proteins. MicroRNAs are short RNA molecules that attach to that messenger chain andchange the message just a little bit, ultimately suppressing the expression of the gene.
    If you glossed over the previous three paragraphs, I don’t blame you. I offered only the most basic information for a little background. For the purposes of this book, the exact molecular mechanisms underlying