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Greyswandir t1_j3clakl wrote

You’re both over and under thinking this lol. So, your DNA encode a ton of information that ultimately determines a lot about your body’s morphology. But that information isn’t a “picture” of what you’ll look like. There’s no coordinate system and your DNA doesn’t “know” where the tip of your nose will be or what your eye color is, etc. Generally speaking your DNA doesn’t know anything about macroscopic space or encode any information about it. DNA directly encodes tiny little parts and machines, and those parts and machines work together in a way that is vastly more complex than the DNA “knows” about.

To give a simple view: DNA codes for proteins in units called codons. Each codon is three bases of the DNA chain (the A, C, G, and T letters you’ve probably seen) and which of those bases appear in what order defines the meaning of the codon. Through a process called transcription and translation, the codon is used to pick a chemical called an amino acid. There are 20 possible amino acids (in humans). The DNA tells the cell which amino acids to assemble in what order. The chain of assembled amino acids folds into a protein (often along with other chains) based on what amino acids go in what order. The proteins do all kinds of things but they’re not smart, they’re structural building blocks or simple machines. But the interplay of simple machines can lead to extremely complex behaviors (like “grow a nose”).

Imagine we have a first protein that sits on the surface of the cell. It bends one way if it’s touching something and bends another if it’s not. We have a second protein that checks the bend of those first proteins and triggers a signal to grow if it’s bent touching something. Now we have a simple little system which means that the cells will grow across an object (like the bottom of a Petri dish) but stop when they run out of room for each cell to be touching the dish. A relatively complex spatial behavior from two simple parts*

And cells are way, way, way more complicated than this, with tons and tons of interlocking signal pathways.

*to be clear: I made the parts and their functions up for my example to just illustrate how the proteins can lead to a spatial behavior without the DNA knowing anything about space. Growing to confluence is a real behavior in many cells, but frankly it’s been a long time since I took cell bio and I don’t remember the exact mechanism.

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Xilon-Diguus t1_j3dfooz wrote

Space can be somewhat inferred by cells through hormone and signaling molecule gradients. So if a central group of cells can start releasing some sort of signaling molecule, and as cells get more distant from that central packet of cells they get less of that molecule, changing their behavior (ie gene expression).

Cells can also divide non-symmetrically, where one cell stays as one type and the other differentiates into a new cell type, creating shape. Cells can pass on information on what genes to express through chemical marks left on the DNA (and the proteins bound to the DNA) telling the new cell what genes to express and what genes to repress.

In the end, though everything does come back to gene expression, which is regulated by a complex network of gene expression networks generated by where the cell originated and what signals it is getting from where it is in the organism.

Interesting the actual genome in the nucleus does have a conserved 3D shape, which has a big impact on how it regulates its genome.

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[deleted] t1_j3di5iq wrote

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aaeme t1_j3e1e20 wrote

It's really hard to explain in words even in a book let alone in a few paragraphs.

Perhaps an analogy:

Langton's Ant is a mathematical curiosity. The idea is an infinite grid. The 'ant' is a marker with position and direction and gets set in motion from anywhere in any direction (the grid is infinite and uniform so it makes no difference). When the ant lands on a cell (a grid square), if the cell is white it turns it black and turns right, if the cell is black it turns it white and turns left. The future behaviour of the ant and the grid is entirely determined by those two rules and the colour-scape of the grid. No other information is present. But the picture it creates is immensely complicated.

Fractals like the Mandelbrot Set and Julia Sets could be another example.

A simple set of iterated rules can produce a very complicated structure and do so repeatedly and reliably. If you don't change the rules you'll always get the same structure.

The degrees of separation between the rules that DNA (combined with all sorts of biochemistry) provide and the physical structures they lead to are as a chasm but they are still pretty reliable and predictable so clones will reliably look almost exactly the same as each other (same rules, same outcome).

Another analogy would be trying to understand how a sequence of zeroes and ones, or the simple rules of machine code, can lead to what we can achieve even just nowadays with AI (outthinking grandmasters at Chess, generating convincing art, etc). It boggles the mind (or should). The rules of DNA (and their interaction with all sorts of biochemistry) are arguably much more complex and varied than machine code so it shouldn't really come as a surprise that it can produce an infinitude of possible biological shapes and yet do so as predictably and consistently as a computer program.

Does that make sense?

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ancientevilvorsoason t1_j3drgxy wrote

Since you get half of your genes from each parent, getting the specific let's say ALIGNMENT of the expression of genes is why your nose looks the same.

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