Why Don’t Identical Twins Always Look Alike?





I thought my response to the other mom was worth sharing with you.

Why Don't Identical Twins Always Look Alike? from hdydi.com









9 thoughts on “Why Don’t Identical Twins Always Look Alike?

  1. My boys had different head shapes in the beginning (and still different today – one of the easiest ways to tell them apart) and I remember the doctor explaining that identical twins start with the same DNA and then are shaped by other forces in the womb (such as placement during pregnancy, during labor/birth, even how much amniotic fluid they had affects head shape and other things.)

    On the other hand, medically my boys have been the exact same, even so much as getting their teeth on the exact same day, milestones within hours of each other, same exact illnesses, same concerns, etc…

    • When I was in college, I actually had the opportunity to work on maternal effect genes. These are genes expressed in the mother in the womb that impact fetal development; the offspring don’t have to inherit the genes themselves to be impacted. For example, differentiation between the head end and the feet end of an embryo is at least partly determined by a gradient of chemicals in the womb. If the chemical are evenly distributed, you can end up with two heads and, obviously, the embryo isn’t viable. Super cool, how our bodies work!

    • Sure thing! I added a little note in the text of this post about mutations that can occur after conception. People definitely tend to think that our DNA is written in stone, but if it were, there would be no cancer, right?

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  3. We had mild TTTS, so one of my twins was bigger at birth. That’s still the case now that they’re almost 8! She is 8 pounds more and two inches taller than her identical sister, which makes it easier for people to tell them apart when they’re together. They also have different hair–one has very curly hair, the other is straight. I think their different experiences in the womb is what has caused them to not be so identical.

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  5. Wow, what a well written article! I was looking for the answer to this question and you explained it so well. Thank you!

  6. My sister and I are identical twins, and get told we are not, how can it be? Etc, etc. because we look so different. But mum had the testing done when we were born. Was 99% or something along those lines accurate that we are in fact identical twins. We are 30 now. :)

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