Figure 1

Inversions as an explanation for intra-strand parity. A, Duplication followed by inversion. If a double-stranded DNA, shown in gray, undergoes duplication and inversion, then the resulting molecule precisely demonstrates the strand parity (both within and between strands). B, A mathematical explanation of intra-strand parity. The n th inversion is illustrated by a box with crossed bars and r _n is the relative length of the inversion within a total fragment of length = 1. Ultimately both A _n and T _n converge to the average of their initial frequencies. See Methods for details. Although a linear double-stranded DNA is shown, this could also be circular. C, A small number of inversions can cause DNA to follow the intra-strand parity. A 40-bp double-stranded DNA fragment in the human mtDNA (position 1875–1914 in accession number NC_001807) is shown, along with the outcome of a single artificial inversion, which has homogenized the contents of the two strands.