Q:

Can a boy and a girl be identical twins?

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Quick Answer

Rarely, a boy and girl may be identical twins. This condition, called Turner Syndrome, afflicts very few pairs of twins. The gender difference occurs when an egg and a sperm pair that begins as two males, loses a copy of its dominant Y chromosome when it splits.

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Can a boy and a girl be identical twins?
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Full Answer

A twin boy and girl may be identical, according to a study found on NCBI, although this situation is very rare. Usually identical twins share the same gender: they are either a pair or boys or girls. In rare instances, however, identical twins form from an egg and sperm that begin as males (sharing XY chromosomes) then change to become a male and female pair. This occurs when one half of the split fertilized egg loses a copy of its genetically encoded Y chromosome. This error generally happens early on the pregnancy. The babies that form include one defined male, who has the proper XY chromosomes required to create male reproductive systems and traits, and a female with XO chromosomes. Although categorized as female, the girl in the dual-sex pair exhibits outward traits of the female gender but carries only one copy of the X chromosome, rather than the XX chromosome used by biologists to classify females as such. Furthermore, the female child often lacks the hormones needed to grow properly and reproduce; as a result, she will be much shorter than the male and lack proper ovarian development. The official term for this condition is Turner Syndrome. It is quite rare and affects very few pairs of twins.

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Related Questions

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    What is the difference between paternal and maternal twins?

    A:

    Paternal and maternal twins, commonly known as fraternal and identical twins, are distinguished by the different ways the multiple pregnancy begins. Identical twins begin as a single zygote that splits into two or more developing embryos. Fraternal twins are usually the result of multiple eggs being present for fertilization.

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    What are dizygotic twins?

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    Dizygotic twins, also known as heterologous or fraternal twins, develop when two separate eggs are fertilized at the same time within the uterus. Dizygotic twins do not have identical genetics and can be of the same sex or of the opposite sex.

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    What does "fraternal twins" mean?

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    Fraternal twins, also known as dizygotic twins, occur when two separate eggs are fertilized by two separate sperm. This results in two babies who are not identical and who do not come from the same egg. Fraternal twins can consist of two girls, two boys or one girl and one boy.

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    How are non-identical twins made?

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    Nonidentical twins occur when a woman produces two separate eggs that are then fertilized by two different sperm cells. The resulting twins sometimes look alike, but have separate genetic identities, like children of the same parents born during different pregnancies. Another name for nonidentical twins is fraternal twins.

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