Chargaff's Rules

 Source

mol % of bases

 Ratios

 %GC

 A

 T

 G

 C

 A/T

 G/C
 PhiX-174

 24.0

 31.2

 23.3

 21.5

 0.77 ¦

 1.08

 44.8
 Maize

 26.8

 27.2

 22.8

 17.0 *

 0.99

 0.98

 46.1
 Octopus

 33.2

 31.6

 17.6

 17.6

 1.05

 1.00

 35.2
 Chicken

 28.0

 28.4

 22.0

 21.6

 0.99

 1.02

 43.7
 Rat

 28.6

 28.4

 21.4

 20.5

 1.01

 1.00

 42.9
 Human

 29.3

 30.0

 20.7

 20.0

 0.98

 1.04

 40.7

* Plant DNA is an apparent exception to Chargaff's rules, however, plant DNA is often heavily methylated. As long as the amount of 5-methyl-cytosine is included in the total amount of cytosine, the rules are obeyed.

¦ Some bacteriophage DNA's (e.g. PhiX174) do not adhere to Chargaff's rules - these phages have single-stranded genomes and are therefore not constrained by the requirements of a double-stranded structure.

Adapted from http://www.mun.ca/biochem/courses/3107/Topics/DNA_history.html.