Can identical twins be different sex?

Question

Mine are in separate sacs and share same placenta

Answer

My father was identical twin and my grandfather had a fraternal twin sister and I also have fraternal twin cousins. Identical twins are always of the same sex because they form from a single zygote that contains either male (XY) or female (XX) sex chromosomes. Boy/girl twins are always fraternal or they can only form from two separate eggs that are fertilized by two separate sperm. Fraternal twins can be either two girls, two boys, or one of each. I also read at some point that in an extremely rare cases the only way for identical twins to be different sexes is that a chromosomal abnormality needs takes place where the female fetus would end up having Turner Syndrome.

Answer

No, identical would be same sex.

Answer

Identical twins would be same gender unless a genetic mutation occur after the zygote separates even then it is so rare.

Mo/Mo twins are always identical. Mo/Di are usually identical; however, in rare situations the placentas can fuse together and act as one - in this case you could have fraternal Mo/Di twins (but they would only be pseudo Mo/Di because they were originally classified as Di/Di).  Di/Di twins are usually fraternal, but there is a 30% chance that the egg separated before implantation (around day 3) and this would lead to identical Di/Di twins. If your Di/Di twins look similar you can have them tested to see if they are identical or fraternal.

Answer

No, identical twins are identical therefore all the parts are the same.

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No they cannot be identical if they are opposite sex.

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Same sex. They have the same DNA. Conceived from the same egg.

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It's extremely rare but yes it can happen. However because of how rare it is it's likely the placentas have fused together and are giving the appearance of just one being there.

Answer

But they are identical since they share the same placenta but are in different sacs?

Answer

Identical twins can only be the same sex. They would have to have the same parts to be identical. The placenta has nothing to do with whether they are identical or fraternal.

Answer

I read an article that said yes but it was extremely rare. Basically, they would have to have an extra sex chromosome, XXY. I dont remember how exactly its supposed to work out but basically, somehow, one fetus expresses the XX and the other fetus expresses XY. I believe its considered a chromosomal defect because of the extra sex chromosome.

Can identical twins be different sex?

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