Editing Chargaff's rules (section)

== Definitions ==

=== First parity rule ===
The first rule holds that a double-stranded [[DNA]] molecule, ''globally'' has percentage base pair equality: A% = T% and G% = C%. The rigorous validation of the rule constitutes the basis of [[Watson–Crick base pair]]s in the DNA double helix model.

=== Second parity rule ===
The second rule holds that both Α% ≈ Τ% and G% ≈ C% are valid for each of the two DNA strands.<ref name=Rudner1968>{{cite journal|pmid=4970114|year=1968|last1=Rudner|first1=R|last2=Karkas|first2=JD|last3=Chargaff|first3=E|title=Separation of ''B. Subtilis'' DNA into complementary strands. 3. Direct analysis|volume=60|issue=3|pages=921–2|pmc=225140|journal=Proceedings of the National Academy of Sciences of the United States of America |doi=10.1073/pnas.60.3.921|bibcode=1968PNAS...60..921R |doi-access=free}}</ref> This describes only a global feature of the base composition in a single DNA strand.<ref name="Zhung2003_externallinks">{{cite journal |vauthors=Zhang CT, Zhang R, Ou HY |year=2003 |title=The Z curve database: a oraphic representation of genome sequences |journal=Bioinformatics |volume=19 [issue=5 |issue=5 |pages=590–599 |doi=10.1093/bioinformatics/btg041 |pmid=12651717|doi-access=free }}</ref>