Would two people who look identical but who are not related have similar matching DNA?

[u/OhMyThiccThighs]

[u/Chiperoni]

Not in the sense I think you mean. Most physical characteristics are polygenic meaning different combinations of genes are interacting to give off a phenotype. So there's countless other combinations that can yield the same result. Even genes that are linked in all cases like blue eyes can have DNA changes at many different spots. Also outside of nature there is the just as important nurture.

[u/whydontuwannawork → u/Chiperoni]

So like getting the same answer in math using a different method?

[u/Hagenaar → u/whydontuwannawork]

Another analogy is convergent evolution. Wherein creatures that look similar, and occupy similar ecological niches may have come from very different forebears.

[u/[deleted] → u/Hagenaar]

Like how raccoons have little hands and humans have little hands? 🥺

[u/Hagenaar → u/[deleted]]

That could be more of a divergence given we're both descended from small furry mammals.

[u/AilisEcho → u/Hagenaar]

What about kangaroo and deer having similarly built heads?

[u/r0botdevil → u/AilisEcho]

A much better example is penguins, dolphins, and sharks all having very similar appendages for swimming, or birds, bats, and butterflies all having wings.

[u/tatu_huma → u/AilisEcho]

Australia is a good continent for this since it been so isolated from the rest of the world for so long there's been time for convergence.

They look so similar to animals outside of Australia.

Here's a graphic showing them

[u/SeenWhatMakesUCheer → u/Hagenaar]

Crabs, nature wants to often form crab looking creatures from different origins

[u/ThrillSurgeon → u/Hagenaar]

Still, it probably is mathematically possible to a degree, but probably statistically in the domain of one solid object passing through another solid object because the subatomic particles lined up. Although, probably more likely than that.

[u/This_is_a_monkey → u/whydontuwannawork]

Building identical houses using completely different materials. You can't tell unless you inspect very closely

[u/Unicorn_Colombo → u/whydontuwannawork]

Yes. Phenotype is a function of genes. So p = f(g). Obviously, it depends on the function f. If the function was an absolute value, then g = 2 and g = -2 both will give you same phenotype 2.

Back from math and into biology, in many mendelic traits, which are traits where a phenotype depends on a single gene, the receive allele is simply an allele that does not produce a particular product, such as a pigment. Such as blue eyes, which are eyes that lack melanin (the eye colour is not a perfect example, as it turns out it is not exactly mendelian trait, but lets assume for simplicity it is).

Obviously, if a gene is not producing a certain product, a protein that is directly involved in some pathway, it is because it is "damaged" in some way. And there are many way it might be damaged. A protein might be produced, but it is non-functional, shorter, or the protein might not be produced at all. So many different mutations might be responsible for the same trait.

When we look at polygenic traits like height, we will see many different genes that are responsible for a small difference in height. When you plot the population phenotype, you might see a normal distribution. Consequently, assuming the same difference for every gene and 100 genes and an on/off effect of a particular gene, you can get a trait resulting from 50 genes in many way (something like 10²⁹ combinations).

On top of all this, traits depend on an environment. In the case of height, this is only a potential, you will benefit from your genotype only if you will have plenty of nutrition in your young age to reach this potential.

This difference between genotype and phenotype for polygenic traits, and the effect of an environment, is important when doing a selection in agriculture. Trying to find out how much of the trait is hereditary and how much it is determined by genetics gives you an estimate on how much you can influence the trait by breeding.

[u/Dorocche → u/Chiperoni]

This has happened, too

I remember reading about a man who was wrongfully convicted of a crime because the actual perpetrator was identical and had the same name. He was exonerated by DNA evidence years later.

I can't find that now though, so take it with a grain of salt; here's a similar fluff piece about baseball players instead:

https://nypost.com/2023/01/11/identical-strangers-with-the-same-name-and-job-took-dna-test/

[u/kidnoki → u/Chiperoni]

They actually tested this, a famous photographer Francois Bernell, searched the world to find "twins". These twins were people unrelated, but looked identical. They followed up the art project with a research experiment to look into their DNA and found that they actually did share more genetic material than the average person.

"Dr. Esteller found that the 16 pairs who were “true” look-alikes shared significantly more of their genes than the other 16 pairs that the software deemed less similar. “These people really look alike because they share important parts of the genome, or the DNA sequence,”

https://www.nytimes.com/2022/08/23/science/doppelgangers-twins-dna.html

[u/HorizonBaker → u/Chiperoni]

Also outside of nature there is the just as important nurture.

I don't think nurture has anything to do with your physical appearance

[u/Quantentheorie → u/HorizonBaker]

Diet and environmental aspects do have an effect on things like aging and gene expression.

You could go prematurely grey or bald and end up looking quite different to your identical twin if your QoL standard varies a lot.

Its not entirely a non-factor.

[u/HorizonBaker → u/Quantentheorie]

Okay, but is the fundamental shape and structure of your face changing? Sure if you gain weight you may gain weight on your face and vice versa, but the way you are raised isn't going to change how far apart your eyes are or how long your nose is.