High Quality Content by WIKIPEDIA articles! xDNA is a modified form of DNA with 8 nucleobases: the four natural bases A, C, G, and T, and four artificial modifications of these made longer by the addition of an extra benzene ring: xA, xC, xG, and xT. A pairs with xT, C pairs with xG, G pairs with xC, and T pairs with xA, so the distance between the two halves of the double helix is consistently greater. The double helix is thus wider and has a longer pitch.