if traits can be inherited without affecting your DNA, can we see those traits when mapping the genome? Or do they to under the radar? Do epigenetics ever change your actual DNA?
In: Biology
Epigenetics are still a very active field of research and we don’t know the definitive answers to these questions yet, so take these answers as “what is known now – the answers may be different in future when more is known”.
So the first part of this is what a “trait” is. That’s more of a colloquial term. What you’re talking about when you say “a trait inherited without affecting your DNA” is the inheritance of an epigenetic modification. The “trait” here is “how much is this particular gene expressed?” rather than “what does this gene do when expressed?”, and differences in the expression of a gene can change the way the gene manifests. To take an example, let’s look at tortoiseshell cats.
Like humans, cats have X and Y chromosomes, and like humans, a cat is female if it has two X chromosomes. X chromosomes do something other chromosomes don’t do: They deactivate themselves. X chromosomes have evolved to have their genes be expressed twice as much as genes of other chromosomes. This is because male cells, which only have one X chromosome, still need to produce the full amount of the stuff on the X chromosome. To compensate for this, female cells randomly deactivate one of their X chromosomes during the early stages of growth as a foetus. Some cells will deactivate the first X chromosome, and some the second. This means each cell expresses the normal amount of each gene, instead of double, but it means that if the X chromosomes aren’t identical, some cells are expressing different types (alleles) of the same gene than others. As it happens, one of the genes that exists on the X chromosome in cats is the gene for coat colour. If the X chromosomes have different alleles of the coat colour gene, then half the cells will express one colour, and half will express the other. This produces a tortoiseshell pattern, as some cells have a different colour to others. So while you might think that the appearance of tortoiseshell cats is a genetic trait, it’s actually an *epi*genetic trait, because it’s the result of the way the expression of genes is modified. However, it’s not an inherited trait – this epigenetic change doesn’t occur in egg cells, so new female cats must create the epigenetic trait again for themselves in their own non-egg cells.
Epigenetic traits cannot be seen in genome mapping, because mapping a genome is only looking at the DNA and going “This particular gene is located here”. It’s also not seen in genome sequencing, which is just taking the entire DNA and writing down the order of bases in the whole thing. We’ll probably develop the technology to make a full sequence of epigenetics in a person at some point in the future, but something to note is that epigenetics are the way that cells are differentiated too. Your heart cells have a different epigenetic map to your skin cells for example, because heart cells don’t need the genes that tell skin cells to make hair follicles, and your skin cells don’t need the genes that tell heart cells to make muscle fibres.
Epigenetics can modify the DNA molecule, but it does so in order to help deactivate the gene, rather than to actually change what the gene says. This process is called CpG methylation, which is where a little bit of carbon is stuck onto the DNA molecule where a G base occurs right after a C base. Epigenetics can only change the actual content of the DNA indirectly, by making the area more or less susceptible to mutation (and of course, this means epigenetics can’t make a deliberate change, only increase the likelihood of some unknown change occurring).
Epigenetics, by definition, doesn’t change your DNA coding so it doesn’t show up when mapping the genome.
It’s changes in which genes are expressed, and when and how, which is caused by the chemical soup surrounding the DNA. You can’t see that from any kind of DNA sequencing.
It’s like handing you a hard drive…you can read it, but you don’t know which files the user is actually cares about.
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