Yes. Identical twins come from one fertilized egg that has been split in two. Therefore, whatever sex the single egg would've been, the twins will be.
Yes.
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.
No. All identical twins are the same sex. Judith and Hamnet were opposite sexes, and so were fraternal twins.
If they weren't , they wouldn't be identical. Sometimes, even though they are the same sex, they do not look exactly alike. Similar, but not identical.
Twins can only be identical if they are the same sex. If they are boy and girl, they are fraternal.
No, monozygotic twins would be the same sex. Monozygotic twins come from one single fertilized egg, or zygote, which then splits to create two separate zygotes which will be genetically identical, or "identical twins", which will always be of the same gender.
Yes.
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.
fraternal twins have two different chromosomes
The DNA of identical twins and of clones is, apart from random, environmentally produced mutations, 100% identical. The only difference is that clones are produced on purpose through advanced bioengineering techniques while identical twins happen as an accident of nature. Identical twins are, in a sense, natural clones.
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.
Twins are identical because they come from the same egg.
No. In order for them to be identical they needed to start off as the same cell and divide so at first their DNA is identical meaning they have the same sex. During development slight changes may occur but the sex always stays the same. Boy-girl twins are always two different cells meaning that they are not identical. The term for boy-girl twins is furturnal. You can however have boy-boy twins and girl-girl twins that are not identical and they are also called furternal. So basically, identical twins start off as one cell that divides and furternal are two individual cells. There is polar body twinning, that's when the egg splits before fertilization, and that can cause a male and a female. This is called semi identical twins or half twins. They share 75% of their genetic markers.