Do fraternal twins share any DNA?
That’s right – at least it is depending on what you take ‘share’ to mean. Identical twins have almost indiscernable genetics (not 100%, but very nearly). Fraternal twins have the same amount of DNA in common that ordinary siblings do: on average that’s 50%. They get roughly half a copy of mum’s and roughly half a copy of dad’s each, so in theory they could have anywhere between 0 and 100% DNA similarity. Edit: Lucinda is talking about semi-identical twins – significantly rarer than identical or fraternal twins. They would have identical DNA from mum and, again, anywhere between 0 and 100% similarity DNA from dad. So on average semi-identical twins would share 75% of their DNA.
