Monday, September 30, 2013

Proactive Genetics: Part 3 - The Results

The Results are in!

In the poll on my blog, the results were different than I expected! 61% thought they would be identical, 26% thought 1/2 identical and nobody thought they're fraternal.   Depending on the day would depend on what I thought.  Somedays I can't tell them apart, other days there are obvious differences to me.  For that reason I mostly think fraternal or inconclusive.

Proactive Genetics said to allow up to 10 days to receive the results of the cheek swab we did on the boys. The results are already in:

---- COPY OF TEST RESULTS #17932-130912 ----

We are pleased to report to you the results of the twin zygosity test that you requested. Analysis of the DNA indicates that Sawyer Joseph Chavez and Logan Martin Chavez are monozygotic, or more commonly referred to as identical twins.

We first isolated DNA from cheek cells from the swab kits that were returned to our lab. We amplified the DNA using a technique called PCR. Next, we analyzed 15 standard DNA markers used in human identity (D3S1358, TH01, D21S11, D18S51, Penta-E, D5S818, D13S317, D7S820, D16S539, CSF1PO, Penta-D, vWA, D8S1179, TPOX and FGA) and determined that the highly variable DNA markers were the same for both twins. Thus, there is greater than a 99.9% probability that the twins are monozygotic.

IDENTICAL!  Wow, I guess all the strangers we run into are right!  I remember reading somewhere that identical twin boys is the least common form of twinning - how cool! 

The reason we didn't know if they are identical or not is because they both had their own sac and their own placenta.  Some doctors and ultrasound technicians assume this means they are fraternal - which is exactly what we were told. But that's not true - obviously.  

Identical twins can have their own, or share, both the outer sac (chorion) and the inner sac (amnion):
    Number of ChorionsNumber of AmnionsNumber of PlacentasWhen Split OccursCommonality
    2 chorions2 amnions2 separate placenta1-4 days after conception25-30% of identicals
    2 chorions2 amnions2 fused placentas1-4 days after conception
    1 chorion2 amnions1 placenta4-9 days65-70%, most common
    1 chorion1 amnion1 placenta9-12 days1-5%, rare

I will have some reading to do about identical twins now, even though I've done a lot already I feel like I need to search out other parents of identicals as a resource for raising them.  I want to make sure they have their own identity, they are their own people. 


  1. Mind Blown!! That's crazy, but so exciting to finally know!! =P

  2. Cool! We had the genetic test done for our boys too... also identical boys. They are the most rare type of twins. Have fun :)

  3. My sister Abby has identical twin girls. They just started Kindergarten. Your kids are growing up so much and are adorable! Love from NE.

  4. I just found your blog through Krystal. I also have identical twin boys (they will be six in June) and was told they were fraternal because of their separate sacs & placentas. But at twelve months we had their DNA tested and confirmed that they were identical.
    My boys are Logan Henry & Jack Sawyer-- so, I like your taste in names! :)