Molar ratios of DNA bases: Chargaff's Rules

 Across a range of species, the molar ratios of the [A] to [T] bases, and of [G] to [C] bases, are equal. The ratio of [A+T] to [G+C] varies among species, with [G+C] bases typically less abundant. For example, in humans the [G+C] content is 39.4%.