It is however inexplicable why, despite the local asymmetries, chromosomes on the whole comply with the Chargaff's second parity rule.
This calculation is valid only for single stranded sequences, which do not obey Chargaff's parity rule one.
Chargaff's second parity rule (CPR2) states that at a lower level of accuracy the first rule also extends to a single strand of DNA [9] [12].
Our results shed light on the 2nd Chargaff's parity rule that was previously applied to DNA sequence containing both genes and intergenic regions.
(Note that the ratios A/G = 1.213 and T/C = 1.214 are the same for the entire chromosome, as it complies accurately with Chargaff's second parity rule [2]).
Furthermore, SLE promotes inverse symmetry at the expense of violating Chargaff's (first) parity rule [7] (CPR1), a key to DNA replication and biological inheritance.
A remarkable feature of mitochondrial DNA is the violation of Chargaff's second parity rule, called strand asymmetry (strand compositional bias) [4], [5].
Chargaff's parity rule, stating that in a DNA sequence contents of A and T, and of C and G, are separately identical [7], was a crucial clue to Watson and Crick's discovery of the double helical structure of DNA [8].
The existence of chromosome trajectories, i.e., deviation from a point, confirms a deviation from the 2nd Chargaff's parity rule, stating that in a single stranded DNA A = T and G = C [5] [7].
The vertebrate group did not display such behavior since it possesses a double-stranded genome, causing CpA and TpG odds ratio to be the same due to Chargaff's parity rule one.
In the present work we address the question of Chargaff's second parity rule and the deviation from it on the level of coding sequences for different groups of species.
