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Analysis: LEGO Genetics

The Real Life comparison:

Despite what movies would have you think, the area of genetics is vastly more complicated than "Add a pinch of X" or "Swap Y with Z". The basis of such inaccuracies come from the simplified way genetics is taught in middle and high school: The double-helix is like a ladder, with the rungs being nucleobases Adenine, Cytosine, Thymine, and Guanine. Each rung fits together, A to T, and C to G. Mix each rung around and presto! You got a tail! This is also how it's portrayed in movies with CG effects showing the double helix spinning around, taking out one rung and putting another in, with the whole thing glowing to show how it's been affected.

This trope gets even stranger when the genes in question come from somewhere besides Earth. DNA is not just "genetic material." It's a specific molecule that we humans, and almost every living thing on Earth, use. It's one of boundless possible candidates for the job. Viruses may use DNA or its sister RNA for their genome. There's no reason to think extraterrestrial genetic material should be the same as ours. Additionally, DNA contains lots of special little sequences besides genes. These include viruses that simply hopped onto our DNA and get copied with it (endogenous retroviruses), sequences which are apparently just "junk" we can't get rid of, and sequences which tell cells how often to turn on each gene and when to shut it down. This also requires that almost all living cells on Earth interpret a gene the same way. That's the genetic code; almost all cells interpret a particular sequence of three "rungs" to mean the same amino acid when they turn the gene on and start making protein. Yet when the plot demands it, an alien has DNA and all the ancillary stuff to be compatible with our genetic heritage. That's so absurdly improbable that if an organism from another planet were to have DNA at all, rather than some other possible molecule, most scientists would immediately start wondering if we had a common origin (or scream "Hoax!") In fiction, aliens have DNA and interpret it just as things which evolved on Earth do. No Biochemical Barriers indeed! Just slap it into our cells and away we go making a Half-Human Hybrid and more.

It should be noted that gene therapy, the alteration, addition or removal of existing genes in an adult organism, exists. Yes, we no longer need the more atrocious method of Eugenics to eradicate debilitating genetic diseases. However, it can be more problematic than presented in fiction, and can wear off after a little while. Additionally, it normally requires very complicated surgery (or the use of gutted viruses) to carry out; you can't simply inject some foreign DNA into your blood and wait for the mutations to take place. However, an evidence for the plausibility of gene therapy lies in the existence of Endogenous retrovirus DNA. One of our ancestors got infected by a retrovirus, which made its way into the said ancestor's germ cells. Bingo! Now his/her children inherit the virus DNA with the parent DNA, until this day. Some of the endogenous retrovirus DNA has since mutated and became junk DNA, but some of those viruses are actually still active and facilitating mutations and evolution, for better or for worse (like helping the embryo implant in the womb, or playing a role in several diseases).

Addition of genes via plasmids (segments of DNA or RNA transplanted between organisms) also exists; it is how viruses reproduce and how bacteria and small beings can adapt. In genetic transfer, plasmids are faster and more efficient in propagating beneficial genes between species than sexual reproduction (which was only useful due to multicellular organisms lacking plasmid capabilities), and this is why bacteria can share antibiotic-resistance genes so fast and easily. Human experimentation has reproduced this, but this is limited to adding new traits to cells. So far, said cells may propagate, successfully integrate into an organism and produce a blood vessel network, but this can only happen in the embryonic stage, and in most cases are yet incapable of forming complicated structures typical of most organs by themselves. However, genetically altered cells may still be used to produce proteins and hormones an organism wouldn't be able to create naturally due to genetic illness, for example giving diabetics the capability to produce insulin and live normally.

The Hox Genes

The Hox genes are an extraordinarily old chunk of dna which seems to date back to the first organism with proto-limbs and bilateral symmetry. They are found virtually unaltered in all branches of complex life, and as best we understand them, they serve as the basic toolkit for generating a body plan. These are, in essence, the bricks for playing Lego Genetics.

Research and experimentation in this field is somewhat young, and warrants careful handling by potentially invoking 5, possibly 6, of the Scientific Sins simultaneously. What has been learned so far is that these genes represent fundamental "syntax calls" in the same sense as computer code. These are the genes that tell the body things like how many limbs it should have, where they should be placed, how to assemble its scales, feathers, or fur, and what colors these should be. All other genes seem to either code for chemical assemblies, or serve as on and off switches for the hox genes. All complex organisms on earth also seem to have the genetic equivalent of a ".init file" called a Homeobox, a shortnote  sequence of genes loosely reflecting its actual structure from head to tail, each chunk of which triggers a particular "programmed" sequence of hox genes. Translating this into pseudo code, the homeobox of a fruitfly would read roughly something like this:

while(head)
do(build(mouth),build(top_of_head),right_left(build(antennas)), right_left(build(brain_eyes))
do(build(head))
while(thorax)
do(right_left(build_front_legs))
do(build(thorax))
do(right_left(build(wings))
do(right_left(build(middle_legs))
do(right_left(build(rear_legs))
do(build(abdomen_a))
do(build(abdomen_b))

the build(front_leg) function might look something like
do(build(leg_section))
do(build(joint))
do(build(leg_section))
do(build(joint))
*This is the long part of the leg:*
do(build(leg_section))
repeat
repeat
repeat
repeat
do(build(joint))
do(build(foot))

What is interesting about these genes is that they are exactly as modular as this would make it seem. One common mutation in fruit flies replaces the Build(antenna) call with a call to Build(front_leg)The result is a fruit fly with perfectly formed legs on its head instead of antenna. Another duplicates the Build(abdomen_a) gene- this gives you a fly with an extra body segment. Similarly, when someone is born with six perfectly formed fingers, its because their build(fingers) section had one extra repeat tag. Like a really good or really bad contractor, when the blueprints ask it to build something odd and the measurements its told to use don't quite add up, it just makes it work as best it can.

The Just Think of the Potential sets in with this: given that all organisms use this same basic template, with tweaks in execution of the "programs" rather than the hox genes themselves making feathers instead of scales or hands instead of fins, the only thing preventing copying the "instructions" for, say, butterfly wings into the genome of a frog and calling this program at the right time an place in the frogs development, is the Square/Cube Law. And the metabolic nightmare of figuring out what extra proteins the butterfrog would need to be able to produce in order to construct said wings successfully. And then what you would have to tweak to make those proteins not kill the butterfrog. And then how to make the butterfrog not hunger for human flesh. Theoretically, however, once the Hox genes are fully decoded and well understood, the only thing preventing Mix-and-Match Critters is a lot of debugging on the genetic code that you copy and paste together out of monitor lizard, bat, and bombarder beetle dna.

For more information, try UsefulNotes.Genetics or (if you can handle the Techno Babble) The Other Wiki.

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