How is genetic memory encoded in DNA?


The Wikipedia page is very short:
And it refers to a Lamarckian process? The linked article is a little bit woolly. Are there any known studies definitively showing that genetic memory is encoded in DNA? What can be encoded? How much?

In: Biology

It isn’t?

Genetic memory is an idea that’s been proposed to explain certain perceived phenomena in individuals’ psyches. But really it’s just a speculative term for what evolutionary biologists call “behavior.”

Behavior is clearly heritable, so there is a genetic aspect to behavior. (But the link between cognition and genes is… complicated, to say the least.) An inherited behavior might seem like a “memory” encoded in one’s genes.

If your parent was alcoholic, it’s possible that you would inherit, genetically, this behavioral trait. You don’t “remember” the alcoholism, you’re just expressing the same behavior as your parent.

DNA is more complicated than just the sequence of ACGT nucleotides. As far as I know, the entire complexity of it is not yet fully understood.

One thing we do know is that some genes can be turned on and off by chemically modifying a nucleotide, without changing the sequence. So you could have a methylated nucleotide instead of a regular one, and that carries extra information about whether the gene will be expressed.

There was one study where they bred a fear instinct into a second generation of lab rats (if I remember correctly) by scaring their parents with a specific stimulus and then breeding the scared rats.

You’ve stumbled upon a highly complex topic that practically remains entirely unknown. I don’t like the term genetic memory, it’s too vague and inaccurate.

It’s going to be quite difficult to explain this, I have to find a balance between sacrificing brevity for clarity and sacrificing clarity for maintaining reader interest that would easily be lost if the comment is a thesis.

I take it you understand the concept of genetics. Your DNA has a 4 letter alphabet, it is stable and protected, carried from generation to generation, vertically transmitted. It’s the blueprint for the majority of what you are at the biological level. But that’s not all, there is something called epigenetics. It’s a modification that doesn’t alter this alphabet yet affects it in a way that can, but doesn’t always, get carried vertically (to progeny). To give a concrete example that aids in understanding, DNA is highly dense due to its enormous size, and to be compact, it is wrapped around proteins and then that is coiled further and further. Eventually you have an ultra dense chromsome that leaves no place for the reading/transcribing machinery to be recruited such that the information can be turned to product. To read a specific part of the DNA, the cell needs to slightly loosen the region of interest, exposing regions with codes that recruit this machinery. Epigenetic modifications can be on the proteins the DNA is wrapped on (making them tighter or looser or completely sealed away) or on the DNA itself, in places like those recruitment codes, helping or preventing the recruitment.

Why do we have this system? Well it seems our cells keep showing more and more facets of their complexity, which shouldn’t come as a surprise seeing how behaviorally complex we are even though we can almost be summarized in some 800 megabytes of data. These epigenetic modifications are actually influenced by nurture (as opposed to nature), so in a more scientific lingo, it serves to link genetics to environmental factors. What’s interesting though is that, depending on the circumstances, some of these modifications can be permanent and they can reach the germ line, meaning eggs and sperms can carry them too, which means your children can be affected by things that happened in your environment.

But when discussing neuroepigenetics things are more complex. Aversive reactions for instance (fear emotions from a given concept or object) affect the neurons, so how does this get to your germ line? Well we don’t know. But we do know the timing really matters. Does it happen to the mother while you’re *in utero*? If so it can affect your germ line, which means your progeny and you can carry those modifications. This concept gets far far more complex and this is where I invoke the principle above about sacrificing clarify for reader interest. But the bottom line is that there is a lot we don’t know, but evidence shows vertical transmission of behavior can certainly happen.

If you have a scientific aptitude and would like to really dig into it, here is an absolutely brilliant paper on the topic:

BTW, I oversimplified a lot of things about epigenetics. Keep in mind these modifications come in dozens of flavors (covalent vs otherwise for example) and affect dozens of types of targets and likely thousands of actual targets.

Edit: English

I mean, even saying genetics makes this a bit difficult to ELI5, but I’ll try. And since it’s ELI5, I’m going to stay high level and broad so this may be a bit inaccurate in some places for simplicity.

But it’s the idea that certain behaviours may be hardcoded into our genetics instead of learned. For the most part, genes can only significantly pass on if there’s an advantage to having them, so the implication is that some genes may give us an advantage (at living or making babies) specifically by predisposing us to certain behaviours or fears. This is a lot harder to explain with higher organisms, so let’s look at some gross-assed flies that I would never actually mention to a 5yo.

For example, certain parasitic flies lay eggs in the brains of crickets. If we literally measure the brain activity of these flies, we can see that they are born with neurons that excite far more readily when they recieve auditory input in the specific frequency of their prey —

OR, to be more ELI5, these flies are born with a brain that will, from birth, already draw them to the exact type of noise their food/sexy-time-holes make.

It’s not that these organisms need to *learn* to associate these sounds with the correct insect so that they can become effective hunters. It’s that they’re already born with a complex profile of genes that will create a brain already designed to react to and draw the flies to the crickets they so desperately want to pop a few eggs into.

The phenomenon described in the article is just a fancy way of saying that organisms with a nervous system tend to have basic “instincts”. So, really the question is how instincts like wanting sex, or looking for certain flowers in bees, can be passed down within a species.

The short answer is that a brain is a machine that has the interesting property that its “wiring” will change its behaviour. In some parts of the brain the wiring may be protected from changing a lot, while in other parts of the brain the wiring can change quite easily and quickly. The wiring that is protected from change is how “instincts” are encoded, babies are simply born with it because their genetic code from their parents has pre-encoded their brain with this wiring. For example, equestrian animals like horses can be up and walking around minutes after their birth because their brains already contain all the wiring they need to understand how to do this, a really useful adaptation for a wild animal that needs to run away from predators!

The wiring that is allowed to change is how brains are able to “learn” from “experience”. Most parts of the brain can change a little bit, and in “smart” animals it is typically the case that change is easier or that the amount of tissue that holds the wiring is greater. Humans have brains that are both very good at changing and also contain a lot of the tissues that contain the wiring, so we have a huge advantage over other animals.

As to how the pre-wiring can be passed down genetically, well that is a very similar question to how any part of the body gets passed down. The pre-wiring is a physical aspect, just like having arms or having hair in one place instead of another. The same genetic mechanisms that encode these important physical parts of your body also encode the physical layouts of the wiring in the brain that create instincts.

EDIT: I see from some other posts that maybe you’re asking about Epigenetics? This is a little different from instinct in that it’s more like a “temporary” genetic memory. In short, your genetic blue print can be though of like a drawing of a building. The drawing tells the workers how to build the building. Epigenetics is like footnotes in the margins that get added over your life time as the builders have to try to overcome realities in your life. For example, starvation can cause your body to add epigenetic markers in your DNA that alter it to increase the production of certain chemicals that help you to survive starvation. Recent studies have suggested that a baby forming in the mothers womb can maybe inherit some of these “footnotes” into their own DNA as they are forming. This is a way for the mother to directly pass down some useful information to her baby because if the mother is starving a lot, then it’s probably useful for the baby to have DNA that is already prepared for that.