A good way to visualize the process: Let's say that you and your partner each comes to your relationship with a set of favorite family recipes. You may contribute a blue-ribbon chili recipe, and your significant other may bring a killer lemon meringue pie to the table. But it's not just two recipes, it's hundreds, maybe thousands. (The human genome has some twenty to thirty thousand genes, after all.)
Some on index cards, some in books, some on torn-up shreds of cocktail napkins. So what do you do with all these cranberry mold recipes? Stuff each and every one of them in the kitchen drawer. Now it's hard to sift through them, you don't have access to many of them, and you really can't find what you want.
minute before and forty-five minutes after their partner's ejaculation have a higher tendency to retain sperm than those who don't have an orgasm.
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Unless ... (you knew there was an "unless" coming) you get them organized, say, by sticking hot pink Post-it notes on the recipes you really want to access quickly.
You tag your favorite recipes, so you can quickly search, find, and put them into action.
That's the way epigenetics works.
Genes are like recipes -- they're instructions to build something. Both mom and dad contribute a copy of their entire recipe book to their offspring, but for many genes, only one copy of each recipe will be used by the baby. Mom and dad have the same recipes (one for eye color, one for hair color, one for toenail growth rate, and so on), except they may have slightly different versions of those recipes (they're called alleles). For example, eye genes are either brown or blue or green.
For such genes, you express only the gene from your mom or dad -- that is, only one copy is active, but not both. In some cases, neither copy will need to be expressed: Eye color matters only to eye cells; a liver cell doesn't need either mom's or dad's eye color gene to be cranking away.
So how does a cell turn off the 24,999 genes it doesn't need and turn on the few it does? Every cell -- and there are around 200 different types in the body -- needs to know which few genes are relevant for it, and, of those genes, whether mom's or dad's is going to be expressed. As with the kitchen drawer full of recipes, the genes alone are useless unless there's a way to find what you need when you need it. There is. Your body puts biological Post-it notes called epigenetic tags on certain genes to determine which genetic recipes get used. This tagging happens through a couple of chemical processes (such as methylation and acetylation), but guess what?
Actions you take during your pregnancy influence these processes and determine where the Post-it notes go and which genes will be expressed, ultimately affecting the health of your child.
When DNA gets tagged, it changes from being tightly wound around those histone proteins to being loosely wound, making the genes accessible and able to be expressed. At any given time, only four percent of your genes are in this accessible state, while the rest can't be actively used in the body. By determining which genes are turned off and which are turned on, epigenetics is what makes you unique.