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Why is it that fraternal twins are almost always the same sex?

Best Answers

About a third of fraternal twins are boy-girl pairs, and about two thirds are same-sex pairs. This makes sense if you consider that there are three possible combinations: GG, BB, and GB. read more

Identical twins are always the same sex and blood type. They almost always share the same placenta but may also have two separate placentas. Depending on when the egg splits usually determines if identical twins will share the same placenta, and/or chorions and amnions. read more

(That's also why identical twins are almost always the same sex.) Fraternal twins, however, don't always look alike. They usually bear a family resemblance, but no more than any other pair of siblings born separately would. read more

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Fraternal Twins vs Identical Twins - Difference and ...
Source: diffen.com

Further Research

Facts About Identical Twins
www.multipletreasures.com

Identical Twins or Fraternal Twins?
www.twin-pregnancy-and-beyond.com