“DNA methylation: it’s like a chastity belt for your chromosomes.”

We humans have a lot of genes — twenty or thirty thousand, give or take a chromosome. But we also have a problem. All those genes are packed into the DNA of each and every one of our cells. You’ve got genes for hemoglobin next to genes for neurotransmitters next to liver enzyme genes next to the ones that tell your left foot to grow toenails. The whole caboodle, in every single cell.

You can’t have all those genes turned on at once, in all the cells. It’d be a disaster. Think of your DNA as a big walk-in closet full of clothes. Some things go together, some things clash, and other things you only wear for holidays — or when senile-assed Aunt Clara shows up to see the stupid lop-eared bunny suit she bought you. But you don’t wear everything you own all at once. That would make you a crazy person.

So it goes with your cells. Depending on where they live — in a little row house along the spinal column, maybe, or a brownstone in the colon — they want to fit in with the neighbors and express the right set of genes. When in Rome, do as the Romans. And when in the respiratory system, don’t spew out growth hormones. That’s not your job, bunnybutt.

There are several ways that cells can shut down or “silence” genes, but one of the most common is DNA methylation. It sounds complicated, but it’s actually pretty simple. To make a protein in a cell, a bunch of enzymes have to get at the bit of DNA coding for it. Those enzymes read the code into RNA, and the protein is built from that. “Methylation” means taking a methyl group, a single-carbon molecule similar to methane, and glomming it onto that DNA structure like a wad of used chewing gum.

Slap enough methyl groups onto a stretch of DNA, and those RNA-making enzymes can’t get at it. Any genes in the neighborhood get completely shut down, like a Honda running out of gas or a dudebro wearing Axe cologne. Even better, when the cell divides, the DNA methylation pattern gets passed down the line. So it’s a great way for specialized cells to shut off genes they have no business fiddling with — basically a permanent genetic cock block.

Though critical for development in mammals — pssssst, that’s us — DNA methylation isn’t used in the same way by all species. Fruit flies, for instance, apparently have better things to do with most of their DNA, and yeast haughtily looks down its nose at DNA methylation.

Or would, if yeast had a nose. Or eyes. Or the genes for being haughty.

In other organisms, DNA methylation comes up a lot. Some — humans and tomatoes, for two — use it to silence potentially harmful genes inserted by viruses into the genome. DNA methylation tends to decrease over time, so it can be used as an indicator of aging. And it’s been linked to diseases like cancer, Alzheimer’s and atherosclerosis, and could offer clues about how those conditions develop.

So DNA methylation is pretty important. Without it, all our cells would crap out all the possible human proteins and we’d be big unregulated oozing blobs of cytoplasm. Like a certain amorphously-shaped cartoon character with a distinct lack of impulse control.

And that’s not attractive. I don’t care how cute a bunny suit you slap on it.