Girl/Boy Identical twins?

On August 9th we found out we were having a girl and a boy. We mentioned that at least we knew now they were fraternal and the tech said not necessarily. She said there was some confusing way that they could still be identical... this made no sense to me. Then a few days ago we mentioned to a guy at church (who happens to be a twin, his twin a girl) that we had b/g twins coming and he asked if we knew if they were identical or not. Hmmm? He said the sex is not one of the things that makes identical or not. Am I just totally missing the boat here? I have been through anatomy in HS and College and I was taught that identical was 1 egg 1 sperm that unite and then splits, leaving 2 EXACT replicas. Since the sex of a baby is actually determined within the sperm then if there is only 1 sperm and 1 egg and it is a xy( boy) and splits the results are identical twin boys. Did I sleep through the genetics class that discussed how a boy and girl twin could be identical?

 

There is one weird exceptional thing that can result in b/g ID twins--I forget the name, but will try to find it. The vast, vast majority of b/g twins are definitely not ID, so you can safely assume yours are not ID.

eta: I found it.

You can see this is exceedingly rare and not something you need to concern yourself about.

 

it's extremely rare but it's essentially a genetic disorder where the original egg has 3 gender chromosomes (XXY) - when the egg splits, one half keeps an XX and the other keeps an XY. i think i read somewhere that there are only 6 known cases in the whole world & it's usually accompanied by additional difficulties, genetic issues, developmental issues, etc. i don't know the actual term for it though.

 

I found this excerpt in this article. ....

However, there have been a few reported cases of a genetic mutation in monozygotic male twins. For some reason, after the zygote splits, one twin loses a Y chromosome and develops as a female. The female twin would be afflicted with Turner Syndrome, characterized by short stature and lack of ovarian development. It's extremely rare; less than ten cases have been confirmed. Given the odds, it's safe to assume that 99.9% of all boy/girl twins are fraternal.

I'd say yours are fraternal ... at least that would be the better outcome.

Congratulations !!

 

Yep, it is possible although very rare like the others have said. In fact, there's a former TS member that this was the case for. Her little girl did not make it due to the genetic issues involved. Her son has done awesome however.

 

Having b/g twins myslef most people don't think. I get asked all the time if they are identical or faternal. I don't worry about the 3-6 cases ever that is the exception, but just say to be identical, they have to be identical in every way including gender. Most people don't know much about twin or how it happens.

 

Very interesting... I would never have guessed it possible and was just shocked that that someone would ask if a b/g twin was identical. I am sure mine are fraternal also but was curious as to how this could be... Thanks for the info!

 

Just the first of a bazillion weird questions that you'll get about twins! I am always surprised at how little medical professionals know about twins too.. I got lots of weird questions from the U/S techs.

 

There is also another really bizarre way they can be "identical" though they are considered more 1/2 ID. It's explained thoroughly in Having Twins by Elizabeth Noble. They are called Sesquizygotic in which the egg splits before it is fertilized and then is fertilized by 2 different sperm. So...1 egg split in 1/2...2 sperm - 1 for each 1/2 resulting in 1/2 ID. These types of twins can result in boy/girl 1/2 ID. This also is extremely rare but has been known to happen. It's explained in great detail in the book. Basically they do not look anything alike and are, for all practical purposes, fraternal. But, in all reality, they are 1/2 ID. Confusing, I know.

And, I agree!! This is only the 1st of MANY absurd questions you will be asked as you star your twin journey!! We get asked all the time if our red/blond haired twin boys are ID. One day we got asked if our youngest 4 were "all twins". LOL! Ummm....do you mean quads??? Another day a lady asked if "those 3 boys are twins". About a month ago we had 2 different people, upon finding out we are expecting our 2nd set of twins, asked why we continue to take fertility meds when we are perfectly capable of having children. I couldn't help but laugh. Some people....most people...just don't think!

 

We get some looks and comments too.... Most people when they find out say "Oh are these your first babies?" When we tell them they are number 7 and 8 they get all weird on us. We get the your crazy comments, are you Catholic or Mormon quesitons (no to both) Have you heard of birth control? (Yup) Did you use fertility drugs? Ummm really number 7 and 8,, does it seem we need help!! I am sure it will continue to get weird but sometimes I just wish people could just say Congrats and then shut their mouths!!

 

Just wait until they're born .. it get's even more bizarre ! :laughing:

The boys dad and I have 8 children (3 his, 3 mine, the twins ours) and people can get SO invasive with their questions. Plus you're going to get asked if they are identical at least once a day .. even after you tell them they are boy/girl and one is dressed in PINK the other BLUE.

 

IMHO, I don't know what the big deal is...identical or fraternal. And these DNA tests to find out if they are identical. Why can't we just be thankful we were blessed with not one but two babies when there are so many women struggling to have one?
Just my two cents. :unknw:

 

I guess the only reason to know if twins are identical or not are for medical reasons, which usually only concern the parents and medical support staff.

besides the "are your b/g twins identical or fraternal?" I also get "does it run in your husband's side of the family?" when I tell them that nobody in my side of the family has twins.

 

This is what I was going to comment about... they wouldn't technically be identical, would they?

 

for me, it matters because we plan on having more - i want to know whether our chances of having twins again are higher or not. in our case, because our girls are identical we don't have a higher chance of having twins again. it would have factored into our decision.

 

I think for me it would have made a difference had they been the same sex if they were identical or not for medical reasons also. What if one got sick and needed a transplant or something serious... knowing they were identical would make a huge difference.... but since mine are fraternal this was more an area of interest... BTW if you have fraternal twins you are more likely to have twins again? Good thing we are done then!! I don't think I could handle 2 sets of twins already having 6 with twins on the way!

 

People are crazy. After telling my aunt that the girls were Id she asked if they were paternal... I love the whole running in the family question! The girls are the 17th set out of 20 in 4 generations. We have 5 sets this generation ( one of each normal type, b/g, b/b frat, b/b id, g/g frat and g/g id). I have a 86% chance of having twins again even though my girls are id

 

I was curious to see what B/G identical twins would look like so I googled it.. they do look alike!

http://michaelandbrookehall.blogspot.com/2007/01/identical-twins-one-boy-one-girlwhat.html

 

Wow they do... as they get older I wonder if one takes on a more feminine look or masculine? Where does the genetic disorder lie? Would they be infertile? Very interesting situations.

 

Fraternal twins are usually genetic and having them does increase you chances of having twins again.