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Unlike identical twins, fraternal twins come from two separate eggs each getting fertilized by a separate sperm. Now these sperms can both carry an X chromosome or a Y chromosome giving rise to fraternal twins of the same gender. But at times one could carry the X chromosome and the other could carry the Y chromosome resulting in twins of opposite gender.

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Q: Why do fraternal twins don't have to be of the same sex?
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Are fraternal twins never the same sex?

Fraternal twins can be the same sex or opposite sexes. It doesn't matter.


If a boy and a girl are twins are they faternal twins or twins?

Twins can only be identical if they are the same sex. If they are boy and girl, they are fraternal.


Was Shakespeare's twins identical?

No. All identical twins are the same sex. Judith and Hamnet were opposite sexes, and so were fraternal twins.


What is combination of chromosomes XY for fraternal twins?

If two fraternal twins have the XY sex chromosomes, they will be male.


Can conjoined twins be different gender?

Nature has various safety valves. That is one of them. Conjoined Twins are identical twins with a natural connective bond, therefore they always take the same sex. Fraternal twins, like the fictional Bobbseys, can be Boy and Girl.


Do conjoined twins have the same sex?

Yes. Conjoined twins are always identical (monozygotic) twins, and identical twins are always the same sex.There is a theoretical case where identical twins could be opposite genders, when the babies are female but in one of the females, a branch of one X chromosome breaks away; however, I don't believe this has ever been observed.


Does 2 sacs and one placenta mean fraternal twins?

I am pretty sure because that is how my twins are at the moment that one placenta and two sacs mean identical twins more often than fraternal and more often identical if they are the same sex


What are twins that dont look alike caled?

Fraternal. They develop from separate ova and are not genetically identical, so look different, can have different sex etc. Unlike "identical twins."


Can identical twins be of different sexes?

They can be. While identical twins always have to be the same gender, fraternal twins usually are not. However this is not always the case. Identical twins occur because they inhabit the same egg. Fraternal twins because two eggs were fertilized at the same time. So fraternal twins could be the same gender, but usually they are of the opposite gender.


Why can fraternal twins be different genders but identical twins are are the same gender?

Identical Twins are the result of a single fertilized egg spliting in two producing two genetically identical children. Fraternal twins are the result of the mother producing two eggs each fertilized by a different sperm from the father. This can result in opposite sex twins.


How is a fraternal twin different than other twins?

Fraternal means "brother-like." Identical twins result from a single fertilzed egg dividing into two separate embryos so the twins share all DNA. Fraternal twins result from two different eggs being fertilized by two different sperm at the same time. The babies are then born at the same time, but only share 25%of their DNA with each other, which is the same amount that siblings born at different times share. The word fraternal used in social organizations, like "the fraternal order of"...refers to the thought that the members are like brothers to each other. Modern french uses the word frere to mean brother.


If twins aren't identical what are they called?

Twins who are of the opposite sex or do not look alike are fraternal twins ~ not identical. This means that at the time of their conception ~ two eggs were fertilised. In the case od identical twins, one egg is fertilised and split in half.