Twins are traditionally classified as monozygotic (identical) or dizygotic (fraternal). Monozygotic twinning results in genetically identical individuals, whereas dizygotic twins share approximately 50% of their DNA sequence identity, as do full siblings. Sesquizygosity is a third form of twinship, in which individuals share between 50% and 100% of genetic identity. Doctors in Brisbane, Australia have discovered what they say is the world’s second...
