Real-Life Identical Twin Genetics Lesson

My boys attract a lot of attention being identical twins. As a matter of fact, that is definitely the factor that draws most people’s attention. Then, the Down syndrome seals the deal. They are, as the old soul puts it, “too cute to measure!”

Every once in awhile a stranger will ask if I’m SURE they’re identical twins because she/he can tell the difference in their physical appearances. [Yeah, the MDs and genetic testing must be wrong and you’re right. LOL] I also get asked if the boys act exactly the same being identical twins. Do they do everything together? Like all the same things? I guess that assumption speaks to the belief that personality is genetically determined such that identical twins would have genetically identical personalities. This is SOOOO not the way it is. My boys couldn’t be more different from each other despite looking very much alike. Though modern psychology posits that some aspects of personality may be at least partially predisposed (i.e. optimism vs. pessimism) no one is entirely sure how much of one’s personality is determined by genetics versus environmental factors/life experience. It is widely accepted that what happens to a person in life and how they handle it may alter the predisposition and outcome.

Having identical twins, we found there are many things that are predisposed but environmentally impacted as well. So, here’s a couple of really cool examples of genetic preprogramming affected by environmental factors:

[1] Both of my boys have Down syndrome. The duplication error that was present in the original egg cell was duplicated in both eggs when it split. I often ponder the science of this and the fact that the duplication error was programmed into that specific egg cell and duplicated in each of my identical twins. This means that the notion that Down syndrome is merely a mistake that happens during the process of copying the 21st chromosome is a scientifically inept description. Whatever causes the duplication error is already programmed into the egg cell before any splitting or duplicating occurs. Otherwise, it would be possible to have identical twins where one has DS and the other does not… To my knowledge, this has never happened. The triplication of the 21st chromosome is not an accident that happens at the time it’s being copied but rather an altercation in the preprogramming built into the original egg cell. But, the result, the outcome, the prognosis varies from one child with DS to another based on environmental factors. Identical twins with Down syndrome make this a fascinating topic to ponder. My guys happen to be pretty much on par with each other. Throughout the Early Intervention process, the boys received a multitude of evaluations in speech, PT, OT and Special Education. Eerily, they almost always received the same scores on their evaluations… and if not the same then just decimal points apart. Even the therapists were baffled by this. They consistently achieved the same scores but always in different ways. Michael could sit up while Brian could pull to stand but couldn’t hold the sitting position. Brian could jump but Michael could throw the ball. Brian knew his colors while Michael could match. Brian could copy a circle, Michael a line. Over and over again, they achieved the same scores not because they could do all the same things but they could do different things that totalled the same number of points on their evaluations. They are preprogrammed to have Down syndrome. They are very much on par with how this affects them in so many ways. But, what and how they learn, the skills they master and when is absolutely unique to each boy. Very weird!

[2] Children with Down syndrome grow teeth willy nilly. The order and timing has no discernible pattern from one child with DS to another… EXCEPT in identical twins with Down syndrome. Every time a new tooth erupted, it did so first in Michael’s mouth before Brian’s. But their teeth did erupt in exactly the same order just not at the same time. That’s because Michael habitually chews things. He’s chewed the tops right off of every sippy cup straw we own (much to Brian’s chagrin). And, he’s a fearsome meat eater. If you ask Mikey what he wants for breakfast, he’ll tell you a hamburger. Brian will always choose pizza. The more you chew and the harder the object you’re chewing, the sooner you wear away the gums covering the slow growing teeth underneath. Soooo, Michael’s teeth came out earlier than Brian’s by anywhere from a few weeks to a couple of months. Michael’s recently filled in a couple of gaps but we’re still waiting for Brian’s teeth to follow his genetically identical pattern. Very interesting to watch in identical twins.

[3] When we meet new people, inevitably they try to determine one distinguishing factor that will allow them to accurately identify which one is Michael and which is Brian. Aside from the color of their shirts or a temporary boo boo on the side of one’s face, there are a few features that vaguely differentiate them from each other. These, of course, are much easier to detect when you have both boys standing face-forward in front of you (not always possible) so it’s not always a help. It so happens that Michael’s face is thinner than Brian’s and Brian’s face is wider than Michael’s. This is because Brian’s head is wider side-to-side and Michael’s is wider front-to-back though the circumference of their heads are exactly the same. You see, the boys were born 8 weeks premature. That means their heads were VERY soft upon their births. Michael spent 6 weeks in the NICU (battling a C-dificil and NEC infection) where he was rotated from back to front and one side to the other like a rotisserie chicken. Given he was hard-wired and attached to monitors to ensure safe and sound sleep, they kept his head very well rounded. On the other hand, Brian was sent home after only 2 weeks in the NICU. And, given the “Back to Sleep” campaign which has caused a 50% drop in the incidence of Sudden Infant Death Syndrome (SIDS), mostly Brian slept on his back. I did wedge him on his sides nearly every night to round out his head like his hospitalized brother’s, but he wiggled his way out of the wedges and found comfort flat on his back. Key word “flat”. His head, that is! Not desperately so but enough to make the shapes of their heads slightly different which also alters the appearance of their eyes ever so slightly. So, that’s partly how we tell them apart. That and the extra 3 lbs Brian carries around… also environmental!

[4] And, finally, I came across a new example of genetic preprogramming influenced by environmental factors just last night as I was bathing the boys and looking, as I always do, for new marks and freckles on their fair skin. When the boys were born, we did not know whether we were having identical or fraternal twins as they were in separate amniotic sacs. We thought, wrongly, that they were fraternal. As it turns out, 2% of all identical twins develop in separate sacs because the egg splits up in the fallopian tube in the first 48 hours of pregnancy and the two babies travel to the uterus, attach and grow independent of one another in the womb. One of the things that made the NICU nurses pretty sure they were identical twins when they were born was that neither of them had a single mark, freckle or spot anywhere on their bodies. This, apparently, is a rarity as well. It seems most everyone is born with some small birthmark of some sort or another. But, Brian’s and Michael’s bodies were both blank slates. Of course, just living their lives has since left evidence of their experiences on their beautiful skin in the form of scars and freckles. So, Michael has this one little freckle on the right side of his upper back (his wing, as Grandma would call it) for maybe a year now. Brian does not. Or, I should say, did not… until I noticed the smallest little freckle just starting to appear in exactly the same spot that Michael has his!!!!

Think about it. Genetically, their skin is built the same as each other’s but the amount of sun each boy gets is slightly different. Freckles are caused by sun exposure. The boys spend most of their days in close proximity to one another and wearing approximately but NEVER the same clothes… And, last time I checked, the clothes they wear — except for their bathing suit tops — are not UV protected. How much sun one boy gets over the other is variable… ever so slightly variable. Who’s in the shade? Who’s back is to the sun? Who’s wearing a white shirt versus a blue shirt? (Neither ever goes shirtless outside of our home.) They’ve been exposed to ever so slightly different environmental factors. It took more than a year, but that very same freckle, once exposed to it’s quota of sunlight appeared on Brian just the way it had, much earlier, on Michael. Even their freckles are genetically programmed if the environmental stars align just right. How cool is that???

My hubby and I think this is all SOOOO cool! The whole identical twin thing is fascinating to watch up close and personal! So, for those people who meet the boys, agree they look alike and ask “how do you tell them apart?”… We sometimes tell them apart by the shape of their faces which goes along with their slight difference in size. Though they have always measured within 1/4” height of each other, Brian consistently weighs 2-3 lbs more than Michael. Brian=Bigger is easy to remember. (But, DON’T ever say that to or in front of them lest we affect Brian’s self-esteem and make him think he’s fat when he’s not or Michael’s self-esteem making him think he’s too skinny, when he’s not!) Or, we may tell them apart on any given day by who’s missing what teeth or who’s got a visible scar or beauty mark where. But, mostly, we tell them apart by who they are and how they act… by their personalities… because, while these other differences I’ve mentioned are ever so subtle — Brian and Michael are vastly different from each other in personality…. despite being genetically identical twins.


About Maggie

I'm a stay-at-home mother of 3 children including a 15-year-old daughter, the Old Soul, and 11-year-old identical twin boys who've been blessed with an extra 21st chromosome (aka: Down Syndrome). I happily spend my time doing all that I can do -- breaking the proverbial box wide open -- to foster my children's development and then sharing what I learn with you through this blog.
This entry was posted in differences, Down syndrome, genetics, identical twins. Bookmark the permalink.

7 Responses to Real-Life Identical Twin Genetics Lesson

  1. stephanie says:

    That is so cool. What an interesting post. I lovre the freckle appearing in the same spot.I find it all amazing!

  2. They are darling boys! Precious!

  3. SLKozul says:

    Maggie – this was so wonderfully said and it so captures the difference I wish I could explain about my girls – they just are themselves and yet they are so much of each other.

  4. Magige: I thoroughly enjoyed this post! It is all so facinating and how amazing it would be to have identical twins! Just last night, we were talking about how the identical twins that we know all have their own personalities and are really truly two very different people. You are one lucky mama! Your boys are two very lucky little boys.I love your blog. Thanks for sharing all of this and thanks for being soooo positive about DS! I love my daughters extra chromosome (that yes, we genetically made at 48 hours AFTER conception! This still amazes me!) and I love that you do too!

  5. Beverly says:

    They are just so beautiful!

  6. Molly says:

    This is so cool. I'm fascinated by twins, and they run in my family! Your blog is fantastic!PS I'm in Westchester! So we're kind of sort of not really neighbors (right now i'm in NYC. are you going to be around for the buddy walk?)

  7. Bonnie says:

    Great post maggie. It certainly is amazing to have identical twins. Nature vs. nurture always amazes me. (I had the biggest smile on my face looking at those sweet faces. The first baby one just made me gush)

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