So you think B/G twins are identical?? ETA..ETA AGAIN
I have triplets. My girls are identical, my son is the fraternal triplet.
It is IMPOSSIBLE to have identical b/g twins.
IDENTICAL means they are exactly alike.
Boys have a penis, girls have a vagina.......THEREFORE, *NOT* identical. Ugh!
ETA::::Posted a pic of my triplets below so you all can see what identical twins and fraternal triplet look like for those of you who are confused. The girls are identical, same DNA, they shared a sac, have the same blood type (my son has a different type). ;)
ETA 2:::: For those of you name calling like four year olds and telling me I dont know anything...YES. I have seen the Turner's Syndrome study. Please note the area of the report which approximates that:
about 1% of twins MIGHT have a Turner's Syndrome child BUT the article CLEARLY states that technically and medically, they are NOT identical twins. The girl has medical concerns and is usually missing her ovaries. This does NOT make her and her brother identical twins. Thanks for showing your class and name calling though. ;)
ETA 3::: Here is the article another member posted. I have put the text in red that states they are NOT identical, even in the case of Turner's Syndrome. I also changed the title for the final time. Hopefully, most people are happy now. If youre not, please excuse yourself from the post.
Actually, you are both somewhat right. Generally, the answer is no. Identical(monozygotic) twins are always same gender because they form from a single zygote that contains either male (XY) or female (XX) sex chromosomes. However, there have been a few reported cases of a genetic mutation in male twins where one twin loses an Y chromosome and develops as a female. The female twin would be afflicted withTurner Syndrome, characterized by short stature and lack of ovarian development. This situation is extremely rare, so you can tell your husband that you are 99% correct in your assumption that identical twins are always the same sex.
Dear Charles -
When I first read your question, I immediately though "no it can't happen." Fortunately, I poked around a bit on MEDLINE, a large collection of biological and medical articles. The answer leans more towards a "sort-of yes" than a definitive "no."
First, let me tell you a little about how our "genetic" information is packaged, and how it relates to the possibility of having identical twins with opposite genders.
People have 23 sets of "chromosomes" (46 total). A chromosome is like a part of blueprint - it contains a portion of the instructions needed to make a person. You need all 23 sets to make a healthy person. Of these 23 sets, one set determines a person's sex - we call this special set the "sex chromosomes." We have two sex chromosomes,called X and Y. Women have two X chromosomes for their set, while men have an X and a Y for their set.
Identical twins (generally) share the same genetic information. Such twinning happens when a single fertilized egg splits into two embryos early in the course of development. Under normal circumstances, a fertilized egg that is XX (female) will not to suddenly give rise to an XY twin, just as an XY egg that splits cannot give rise to an XX twin.
However, I said under "normal circumstances..." There have been rare reports of male and female "identical twins" (see references below). Truly, none of the twins is genetically identical as they have a different complement of X/Y chromosomes. Their sex chromosomes differ, but their non-sex chromosomes are otherwise the same. I found no instances where both twins had the normal set of 23 chromosomes. Either one or both had genetic anomalies.
How do these very rare events occur?
We can't always tell for certain, but it appears the original fertilized egg may have a significant genetic defect such as extra chromosomes, or fragments of sex chromosomes that become stuck to one of the non-sex chromosomes. In some cases the defects may arise early in development - after fertilization, but either before or after the twinning occurs. In all cases, both twins arose from a single fertilized egg.
Fraternal twins, twins arising from two separately fertilized eggs, are commonly different genders, though they can also be the same gender.
Hope this helps..
- Lynn Bry, MD/PhD
Department of Pathology
Brigham & Women's Hospital
Harvard Medical School
Prenat Diagn 1999 Jan;19(1):72-6 'Identical' twins with discordant karyotypes.Nieuwint A, et al.
Am J Med Genet 1994 Oct 15;53(1):52-5 Monozygotic twins of different apparent sex.Yokota Y, et al.
Am J Med Genet 1991 Nov 1;41(2):239-45 Monozygotic twins of discordant sex both with 45,X/46,X,idic(Y) mosaicism. Fujimoto A, et al.