 So if we look at this diagram here, I talked about the fact that gene was actually converted to the messenger RNA. Chromosomes are the package DNA, and the DNA has many, many genes, and those genes are for specific processes. The cell doesn't express all those genes. It doesn't translate all of those genes into messenger RNA all at the same time. So there have to be ways for the cell to control what actually gets expressed. So often you might have, so in this particular case the gene is listed here with a better drawing of the DNA. There's often a region of the gene that promotes its expression, if it's something that needs to be expressed a lot. And what that promoter does is it binds to the enzyme that translates the DNA into RNA very strongly. And sometimes there are enhancers that are binding to other parts of the DNA and activate our proteins, and those can be a long ways away in the DNA, sort of loop the whole thing over. And so for a gene to be expressed, it requires the interaction of all these different molecules that are responding to the environment of the cell. And so, for example, one of these activator proteins might be triggered by the translation of one gene, excuse me, the transcription of one gene that then gets translated into that protein. And if that happens a lot, you can get more of these activator proteins, which will then maybe promote the transcription of another gene. So there can be a lot of, for example, reinforcing feedbacks. These reinforcing feedbacks can lead to these very specific genes getting expressed, or getting transcribed. There are also some ways to dampen feedbacks in gene expression. And one way to do that is to methylate the genes. So basically the methyl is a carbon and hydrogen group, and it'll bind to the gene, and it can actually then attract other molecules, and then these can actually dampen expression in a dampening feedback. And so a large part of what gets expressed in genes is controlled by the presence of these enzymes, the activator proteins, these methyl groups, and all of these extra factors are called epigenetics. And they're the type of things that control which genes actually get transcribed to produce the messenger RNA, which is then turned into the enzymes.