Development of physical traits in humans

[Hans de Vries]

At what point are human physical traits like facial features and body type set and impossible to change?

 

Would, as an example, altering someone's DNA at age 10 to that of Neil deGrasse Tyson's cause his facial features to diverge significantly from how they would develop with his native DNA?

[Dagl1]

Probably some bone structures will be set, but I suppose (ignoring the full on immune response this would probably elicit) skin colour and any other thing that is dependent on regenerating/remodelling tissue, will at least change a bit. 

Significant is more a measure of how sure we are, I think could definitely notice the difference, but how extreme those differences would be are hard to predict.

 

[Hans de Vries]

What about brain? 

 

Brain is more malleable than bone. Tests on mice have shown that autism and schizophrenia can be reversed by switching single genes on and off.

[Dagl1]

17 minutes ago, Hans de Vries said:

What about brain? 

 

Brain is more malleable than bone. Tests on mice have shown that autism and schizophrenia can be reversed by switching single genes on and off.

They have? Links please, I am interested.

I would say that memory formation potential and hormone related stuff will become different the most, other stuff almost by definition as well but I don't know how much of the initial neuron paths/connections will be able to change, that feels kind of structural. I don't think you will suddenly get Neil, but there will certainly be things that change in how it works in that person, and then many years later those differences and different behaviours will manifest more (I imagine that from the moment that you change this person's genes, him and what he would have become will start diverging a lot). 

 

[Hans de Vries]

autism

https://www.spectrumnews.org/news/reversing-shank3-mutations-in-mice-mitigates-autism-like-traits/

 

schizophrenia

https://www.sciencedaily.com/releases/2019/10/191009132401.htm

[Dagl1]

Thank you!

I would be careful with saying things like:

18 hours ago, Hans de Vries said:

Tests on mice have shown that autism and schizophrenia can be reversed by switching single genes on and off.

The schizophrenia article is about a model for schizophrenia, which requires the loss of a single allele of SETD1A. The risk of getting  schizophrenia increases from SETD1A mutations, but that doesn't mean that by fixing this mouse model we can also fix scihizophrenia, especially if someone has a SETD1A unrelated type of schizoprhenia?

The paper regarding autism talks about how autism related symptons will be lessened in mice by correcting SHANK3, but also that SHANK3 is really rare (aprox 2% of autistic people have mutations in SHANK3). So we are again looking at a mouse model where problems are simulated and fixed. I would say that that is a far way off from reversing autism by just switching a gene off.

"In mice, we can reduce autism- and schizophrenia-like symptoms, caused by specific mutations that are not the only risk factors in autism/schizophrenia in humans." I would feel pretty confident that if we find someone with SHANK3 mutations, or too little or too much expression of SHANK3, and this person is showing autism-like symptoms, it may be helpful to (once we are good enough at it) gene edit SHANK3, but that isn't going to just fix 'autism' in general.)

 

[Hans de Vries]

What about correcting more DNA?

 

If autism in individual X is caused by Y number of DNA fragments, would correcting them correct autism?

[Dagl1]

Pretty sure if you would that in an embryo, and you knew what to tweak then most likely.
If you do it in an adult or a 10 year old, maybe, it depends on how much of those things are reversible, but maybe. 

 

[Hans de Vries]

Even mundane shit like Fecal Microbiome transplant can reduce autism symptoms by 50%

... then what would a full blown DNA exchange do?

[Dagl1]

Isn't this the same question? We don't know (or at least I don't) which parts of autism are reprogammable at age 10, we can only speculate about it. If the gut micriobiome can affect it THAT MUCH, then you could of course argue that even if you change the DNA of the whole head (or even the gut) you may not be changing the gut microbiome, therefore actually having less effect.

But again, at this point is really speculative and I think the question is answered by (bold added by me for clarification) 

21 hours ago, Dagl1 said:

Pretty sure if you would that in an embryo, and you knew what to tweak then most likely (the autism symptoms will decrease or go away completely, maybe).
If you do it in an adult or a 10 year old, maybe, it depends on how much of those things are reversible, but maybe. 

 

 

[Hans de Vries]

My reasoning is that what gut microbiome transplant does is changing gene expression in the brain. 

 

Exchanging entire genome would also change gene expression in the brain but to a larger degree.

As a side question, how are physical traits inherited?

 

For example every person has genes coding for facial features from both his father and mother yet it's possible to look exactly like one parent (my nephew looks like an exact copy of my sister except for slightly darker and more wavy hair, you wouldn't tell them apart if not that) or like a mix of both. How does it work?

[Dagl1]

You inherit them from your father and mother, maybe some combinations make very similar phenotypes, maybe just like with eye color, there can be some genes that are dominant or co-dominant. We inherit DNA (and maybe some epigenetic stuff), DNA leads to protein production, and all the proteins together will determine the phenotype (together with the environment). It is really difficult to predict emerging properties, especially when so many genes interact with each other. Thus by just inheriting the right combination, you may get phenotypes that are very similar.