How different can genetically identical twins get?

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Discussion Overview

The discussion revolves around the extent to which genetically identical twins can differ from one another, exploring the implications of genetics, epigenetics, and environmental factors on their development and appearance. The conversation touches on theoretical simulations of embryology and the complexities of identical DNA in real-world scenarios.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that while identical DNA leads to identical twins, this does not guarantee they are perfect copies at birth.
  • There is curiosity about the degree of epigenetic similarity between monozygotic twins, suggesting that environmental factors may influence their development.
  • One participant shares personal observations of identical twins, noting that even among those who appear very similar, individual differences can emerge, particularly in personality and behavior.
  • Concerns are raised about the limitations of studies on twins, suggesting that they may often select for more alike pairs, potentially skewing perceptions of their differences.
  • A participant questions the feasibility of conducting ethical experiments to observe identical twins raised in different environments, highlighting the complexities of such research.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the degree of similarity between identical twins, with some questioning the assumption that they are perfect copies. Multiple competing views remain about the influence of genetics versus environmental factors on their differences.

Contextual Notes

Limitations include the reliance on anecdotal evidence and personal observations, as well as the ethical considerations surrounding experimental studies involving identical twins raised in different environments.

Who May Find This Useful

Readers interested in genetics, developmental biology, psychology, and the nature versus nurture debate may find this discussion relevant.

Simon Bridge
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Articles like this one tend to lead to speculation about simulating the whole embryology etc so that you can tell what someone looked like starting from their genome.

I've been taking the position that a simulation capable of doing that is unlikely because DNA does not work like that - it is not so much a blue-print as a recipe ... and that is probably going a tad far.

However, I am hard pressed to support this idea, and the state of knowledge has certainly changed since I last looked at this (early 90's - where it was generally considered doubtful that you could sequence fossil, or just very old, DNA.)

Identical human DNA does lead to identical twins ... but they tend to share a womb as well. Would the genetically identical fetuses develop identically in different wombs?

How different can genetically identical twins get?
 
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Simon Bridge said:
Identical human DNA does lead to identical twins

Does it?

I don't know, I am sincerely asking. But somehow I doubt they are perfect copies even at birth.
 
An interesting question would be how epigenetically identical monozygotic twins are.
 
@Borek:
I have known three sets of identical twins ... two sets were very very identical and one were just uncannily identical. But they all grew up together. One of the "seriously you cannot tell them apart" pair hated being identical and took pains to look different and it was still hard. It was only resolved when one got caught in a barbed wire fence and ended up with one of those scars over the eye.

I got to be able to tell them apart by their body-language ... which would take a while.
Seriously, their own parents couldn't tell.

However - via skeptics networks, I have heard that identical twins need not be all that identical. There is a tendency to learn to be identical as kids, and studies have tended to select for very alike twins for subjects.

@Ryan - thanks for the terminology :) that reminds me:

I am (JIC there's a pedant reading this) not including differences obtained through misadventure or surgery.

In a way what I am really asking is "to what extent does your genome determine your appearance?" But I'm trying to be clever. I was hoping that some fertility clinic has implanted identical kids in different mothers and kept track. I doubt we'd get a deliberate experiment of this kind past the ethics committee.
 

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