**7. Nucleotide compositions**

As described above, the intraspecies rule of nucleotide composition was reported by Chargaff in 1950, as the first parity rule [12], and a similar parity rule regarding the single DNA strand was reported by the same group in 1968, as the second parity rule [14]. Using the normalized values to 1 (G + C + T + A = 1), the following relationships are obtained: G = C, T = A, and [(G + A) = (C + T)]. Recently, Mitchell and Bridge [16] reported that Chargaff 's second parity rule is applicable to a single DNA strand comprising a double-stranded DNA, based on many complete genome data among various species. Conversely, we showed that chloroplast and plant mitochondrial DNA and nuclear DNA obey Chargaff 's second parity rule as an inter-species rule [37], and that the second parity rule was applicable to the nucleotide relationships not only in the coding region, but also in non-coding regions compared with those of the complete single DNA strand [37, 38]. When invertebrate mitochondrial DNA is classified into two groups, high C/G and low C/G ratios, nucleotide content relationships may be expressed by linear formulae [37]. However, organellar DNA deviated from Chargaff 's second parity rule and nucleotide relationships were heteroskedastic [16, 39, 40]. The fact that all regression lines based on different kingdoms closed at the same single point suggests that all species descended from a single origin [41]. This is the first demonstration based on scientific evidence that all species were descended from a single origin of life. This concept has been presumed since Darwin's theory "Origin of Species" was published in 1859. Charles Darwin discussed evolution over the course of generations via the presence of "Natural Selection" in "On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life"; however, he discussed neither "a single origin" nor "a common ancestor" of species. The two regression lines of nucleotide relationships based on coding and non-coding regions closed to form a wedge-shape, because both fragments exist on the same DNA strand [37]. Similarly, the two regression lines based on chloroplast and plant mitochondrial DNA also closed to form a wedge-shape [37]. Thus, both organellar DNA independently descended from the same origin in biological evolution. Quite recently, it has been shown that vertebrates are descended from a certain

**15**

**Figure 5.**

*from Sorimachi [36].*

*Visible Evolution from Primitive Organisms to* Homo sapiens

phenotypic expressions over a 3.5-billion-year period.

invertebrate [42]. However, although the phylogenetic trees [7–11] have an apparent single origin, these "facts" are merely mathematical calculation results.

Chargaff's parity rules were originally based on intraspecies phenomena [12, 14], and the rules are applicable to inter-species evolutionary phenomena for nuclear, chloroplast, and plant mitochondria as mentioned above. The rules are represented by the following equations: G = C, T = A, [(G + A) = (C + T)]. As all values are normalized to 1, Chargaff's parity rule can also be represented as: 2G + 2A = 1, A = 0.5 – G, T = 0.5 – G, C = G, G = (G). The lines G and C overlap and the lines A and T overlap, and the former is line symmetrical to the latter against the line y = 0.25, as shown in **Figure 5**. These equations mean that four nucleotide contents can be expressed by just one nucleotide content using regression lines (**Figure 5**), and the two duplicate nucleotide contents (G or C and T or A) are symmetrical. Thus, the four nucleotide contents (two duplicate points) move strictly on the diagonal of 0.5 of a square in nuclear, chloroplast, and mitochondrial DNA, which obey Chargaff's second parity rule. Therefore, biological evolution caused by nucleotide alterations is expressed on the diagonal of a 0.5 square: the "diagonal genome universe" [36], although biological evolution shows a wide spectrum of

*The "Diagonal Genome Universe." Plotting four nucleotide contents normalized to 1 against certain nucleotide content (i.e., G or C content), G and C contents are expressed by (G = G) and (G = C), respectively, and T and A contents are expressed by (T = 0.5 − G) and (A = 0.5 − G), respectively. For example, if G = 0.1 (white dashed line), C = 0.1, T = 0.4, and A = 0.4. White open square, A or T; pink closed square, C or G. The white dotted line represents the line of symmetry (y = 0.25). Similarly, plotting nucleotide contents against T or A content, (T = T), (T = A), (C = 0.5 – T or A), and (G = 0.5 − T or A) are obtained. This figure was adapted* 

*DOI: http://dx.doi.org/10.5772/intechopen.91170*

**8. Diagonal genome universe**

invertebrate [42]. However, although the phylogenetic trees [7–11] have an apparent single origin, these "facts" are merely mathematical calculation results.
