This animation describes the typical ratios of bases in DNA.

In 1950, biochemist Erwin Chargaff published a paper stating that in the DNA of any given species, the ratio of adenine to thymine is equal, as is the ratio of cytosine to guanine. This set of rules became known as Chargaff's ratio, and it was an important clue for solving the structure of DNA.

Depending on students’ background, it may be helpful to pause the animation at various points to discuss different features.