# A 2D graphical representation of the sequences of DNA based on triplets and its application

- Sai Zou
^{1}, - Lei Wang
^{1}Email author and - Junfeng Wang
^{1}

**2014**:1

https://doi.org/10.1186/1687-4153-2014-1

© Zou et al.; licensee Springer. 2014

**Received: **17 August 2013

**Accepted: **10 December 2013

**Published: **2 January 2014

## Abstract

In this paper, we first present a new concept of ‘weight’ for 64 triplets and define a different weight for each kind of triplet. Then, we give a novel 2D graphical representation for DNA sequences, which can transform a DNA sequence into a plot set to facilitate quantitative comparisons of DNA sequences. Thereafter, associating with a newly designed measure of similarity, we introduce a novel approach to make similarities/dissimilarities analysis of DNA sequences. Finally, the applications in similarities/dissimilarities analysis of the complete coding sequences of β-globin genes of 11 species illustrate the utilities of our newly proposed method.

## Keywords

## 1. Introduction

In the recent years, an exponential growth of sequence data in DNA databases has been observed by biologists; the importance of understanding genetic sequences coupled with the difficulty of working with such immense volumes of DNA sequence data underscores the urgent need for supportive visual tools. Recently, graphical representation is well regarded which can offer visual inspection of data and provide a simple way to facilitate the similarity analysis and comparison of DNA sequences [1–5]. Because of its convenience and excellent maneuverability, currently, all kinds of methods based on graphical representation have been extensively applied in relevant realms of bioinformatics.

Until now, there are many different graphical representation methods having been proposed to numerically characterize DNA sequences on the basis of different multiple-dimension spaces. For example, Liao et al. [6–9], Randic et al. [10–13], Guo et al. [14, 15], Qi et al. [16], Dai et al. [17, 18], and Dorota et al. [19] proposed different 2D graphical representation methods of DNA sequences, respectively. Liao et al. [20–23], Randic et al. [24, 25], Qi et al. [26], Yu et al. [27], and Aram et al. [28] proposed different 3D graphical representation methods of DNA sequences, respectively. Liao et al. [29], Tang et al. [30], and Chi et al. [31] proposed different 4D graphical representation methods of DNA sequences, respectively. In addition, Liao et al. [32] also proposed a kind of 5D representation method of DNA sequences and so on.

In these approaches mentioned above, most of them adopt the leading eigenvalues of some matrices, such as *L*/*L* matrices, *M*/*M* matrices, *E* matrices, covariance matrices, and *D*/*D* matrices, to weigh the similarities/dissimilarities among the complete coding sequences of β-globin genes of different species. Because the matrix computation is needed to obtain the leading eigenvalues, these methods are usually computationally expensive for long DNA sequences. Furthermore, in some of these approaches, their results of similarities/dissimilarities analysis are not quite reasonable, and there are some results that do not accord with the fact [7, 9].

To degrade the computational complexity and obtain more reasonable results of similarities/dissimilarities analysis of DNA sequences, in this article, we propose a new 2D graphical representation of DNA sequences based on triplets, in which, we present a new concept of ‘weight’ for 64 triplets and a new concept of ‘weight deviation’ to weigh the similarities/dissimilarities among the complete coding sequences of β-globin genes of different species. Compared with some existing graphical representations of the DNA sequences, our new scheme has the following advantages: (1) no matrix computation is needed, and (2) it can characterize the graphical representations for DNA sequences exactly and obtain reasonable results of similarities/dissimilarities analysis of DNA sequences.

## 2. Proposed 2D graphical representation of DNA sequence

**Relationship between 20 different kinds of most common amino acids and 64 different kinds of mRNA codons**

Codons | Amino acid | Codons | Amino acid |
---|---|---|---|

GCU, GCC, GCA, GCG | Alanine | CUU, CUC, CUA, CUG, UUA, UUG | Leucine |

CGU, CGC, CGA, CGG, AGA, AGG | Arginine | AAA, AAG | Lysine |

GAU, GAC | Aspartic acid | AUG | Methionine |

AAU, AAC | Asparagine | UUU, UUC | Phenylalanine |

UGU, UGC | Cysteine | CCU, CCC, CCA, CCG | Proline |

GAA, GAG | Glutamic acid | UCU, UCC, UCA, UCG, AGU, AGC | Serine |

CAA, CAG | Glutamine | ACU, ACC, ACA, ACG | Threonine |

GGU, GGC, GGA, GGG | Glycine | UGG | Tryptophan |

CAU, CAC | Histidine | UAU, UAC | Tyrosine |

AUU, AUC, AUA | Isoleucine | GUU, GUC, GUA, GUG | Valine |

UAA, UAG, UGA |

**The corresponding triplets of 64 codons**

Codons | Corresponding triplets | Codons | Corresponding triplets |
---|---|---|---|

GCU, GCC, GCA, GCG | GCT, GCC, GCA, GCG | CUU, CUC, CUA, CUG, UUA, UUG | CTT, CTC, CTA, CTG, TTA, TTG |

CGU, CGC, CGA, 0020CGG, AGA, AGG | CGT, CGC, CGA, CGG, AGA, AGG | AAA, AAG | AAA, AAG |

GAU, GAC | GAT, GAC | AUG | ATG |

AAU, AAC | AAT, AAC | UUU, UUC | TTT, TTC |

UGU, UGC | TGT, TGC | CCU, CCC, CCA, CCG | CCT, CCC, CCA, CCG |

GAA, GAG | GAA, GAG | UCU, UCC, UCA, UCG, AGU, AGC | TCT, TCC, TCA, TCG, AGT, AGC |

CAA, CAG | CAA, CAG | ACU, ACC, ACA, ACG | ACT, ACC, ACA, ACG |

GGU, GGC, GGA, GGG | GGT, GGC, GGA, GGG | UGG | TGG |

CAU, CAC | CAT, CAC | UAU, UAC | TAT, TAC |

AUU, AUC, AUA | ATT, ATC, ATA | GUU, GUC, GUA, GUG | GTT, GTC, GTA, GTG |

UAA, UAG, UGA | TAA, TAG, TGA |

*Ψ*to map each of these triplets into a different weight. Obviously, the mapping

*Ψ*shall satisfy the following rule: for any two pairs of triplets (

*X*

_{1},

*Y*

_{1}) and (

*X*

_{2},

*Y*

_{2}), where

*X*

_{1},

*Y*

_{1},

*X*

_{2}, and

*Y*

_{2}are all triplets, if the corresponding codons of

*X*

_{1}and

*Y*

_{1}code the same amino acid but the corresponding codons of

*X*

_{2}and

*Y*

_{2}code two different amino acids, then there shall be |

*Ψ*(

*X*

_{1}) −

*Ψ*(

*Y*

_{1})| < |

*Ψ*(

*X*

_{2}) −

*Ψ*(

*Y*

_{2})|. So, according to the above rule and for the sake of convenience, weights consist of amino acid and codon. Amino acid is the integer part of weight, and codon is the fractional part of weight. Alanine is defined as 1, arginine is defined as 2, and the rest can be done in the same manner. Codons of every amino acid are reordered, so the first codon of alanine's (GCT) weight value is 1.1. We design the detailed mapping rules of

*Ψ*as illustrated in Table 3.

**The mapping rules of**
Ψ

Triplet | Corresponding weight | Triplet | Corresponding weight |
---|---|---|---|

GCT | 1.1 | CTT | 11.1 |

GCC | 1.2 | CTC | 11.2 |

GCA | 1.3 | CTA | 11.3 |

GCG | 1.4 | CTG | 11.4 |

TTA | 11.5 | ||

TTG | 11.6 | ||

CGT | 2.1 | AAA | 12.3 |

CGC | 2.2 | AAG | 12.4 |

CGA | 2.3 | ||

CGG | 2.4 | ||

AGA | 2.5 | ||

AGG | 2.6 | ||

GAT | 3.3 | TTT | 13.1 |

GAC | 3.4 | TTC | 13.2 |

AAT | 4.1 | CCT | 14.1 |

AAC | 4.2 | CCC | 14.2 |

CCA | 14.3 | ||

CCG | 14.4 | ||

TGT | 5.1 | TCT | 15.1 |

TGC | 5.2 | TCC | 15.2 |

TCA | 15.3 | ||

TCG | 15.4 | ||

AGT | 15.5 | ||

AGC | 15.6 | ||

GAA | 6.1 | ACT | 16.3 |

GAG | 6.2 | ACC | 16.4 |

ACA | 16.5 | ||

ACG | 16.6 | ||

CAA | 7.1 | TGG | 17.3 |

CAG | 7.2 | ||

GGT | 8.1 | TAT | 18.1 |

GGC | 8.2 | TAC | 18.2 |

GGA | 8.3 | ||

GGG | 8.4 | ||

CAT | 9.1 | GTT | 19.1 |

CAC | 9.2 | GTC | 19.2 |

GTA | 19.3 | ||

GTG | 19.4 | ||

ATT | 10.1 | ATG | 20.1 |

ATC | 10.2 | ||

ATA | 10.3 | ||

TAA | 21.1 | ||

TAG | 21.2 | ||

TGA | 21.3 |

For example, from Table 3, we will have *Ψ* (GCT) = 1.1, *Ψ* (GCC) = 1.2, *Ψ* (ATG) = 20.1, etc., and in addition, we can propose a novel 2D graphical representation of DNA sequences as follows:

*G*=

*g*

_{1},

*g*

_{2},

*g*

_{3}…

*g*

_{ N }be an arbitrary DNA primary sequence, where

*g*

_{ i }∈ {A, T, G, C} for any

*i*∈ {1, 2,…,

*N*}, and then, we can transform

*G*into a sequence of triplets such as

*G*=

*t*

_{1},

*t*

_{2},

*t*

_{3}…

*t*

_{ M }, where

*M*= [

*N*/3] and

*t*

_{ i }is a triplet of DNA for any

*i*∈ {1, 2,…,

*M*}. Thereafter, we can define a new mapping Θ to map

*G*into a plot set as illustrated in the formula (1).

**The complete coding sequences of β-globin genes of 11 species**

Species | Complete coding sequence |
---|---|

Human | ATGGTGCACCTGACTCCTGAGGAGAAGTCTGCCGTTACTGCCCTGTGGGGCAAGGTGAACGTGGATGAAGTTGGTGGTGAGGCCCTGGGCAGGCTGCTGGTGGTCTACCCTTGGACCCAGAGGTTCTTTGAGTCCTTTGGGGATCTGTCCACTCCTGATGCTGTTATGGGCAACCCTAAGGTGAAGGCTCATGGCAAGAAAGTGCTCGGTGCCTTTAGTGATGGCCTGGCTCACCTGGACAACCTCAAGGGCACCTTTGCCACACTGAGTGAGCTGCACTGTGACAAGCTGCACGTGGATCCTGAGAACTTCAGGCTCCTGGGCAACGTGCTGGTCTGTGTGCTGGCCCATCACTTTGGCAAAGAATTCACCCCACCAGTGCAGGCTGCCTATCAGAAAGTGGTGGCTGGTGTGGCTAATGCCCTGGCCCACAAGTATCACTAA |

Chimpanzee | ATGGTGCACCTGACTCCTGAGGAGAAGTCTGCCGTTACTGCCCTGTGGGGCAAGGTGAACGTGGATGAAGTTGGTGGTGAGGCCCTGGGCAGGTTGGTATCAAGGCTGCTGGTGGTCTACCCTTGGACCCAGAGGTTCTTTGAGTCCTTTGGGGATCTGTCCACTCCTGATGCTGTTATGGGCAACCCTAAGGTGAAGGCTCATGGCAAGAAAGTGCTCGGTGCCTTTAGTGATGGCCTGGCTCACCTGGACAACCTCAAGGGCACCTTTGCCACACTGAGTGAGCTGCACTGTGACAAGCTGCACGTGGATCCTGAGAACTTCAGGCTCCTGGGCAACGTGCTGGTCTGTGTGCTGGCCCATCACTTTGGCAAAG |

Gorilla | ATGGTGCACCTGACTCCTGAGGAGAAGTCTGCCGTTACTGCCCTGTGGGGCAAGGTGAACGTGGATGAAGTTGGTGGTGAGGCCCTGGGCAGGCTGCTGGTGGTCTACCCTTGGACCCAGAGGTTCTTTGAGTCCTTTGGGGATCTGTCCACTCCTGATGCTGTTATGGGCAACCCTAAGGTGAAGGCTCATGGCAAGAAAGTGCTCGGTGCCTTTAGTGATGGCCTGGCTCACCTGGACAACCTCAAGGGCACCTTTGCCACACTGAGTGAGCTGCACTGTGACAAGCTGCACGTGGATCCTGAGAACTTCAAGCTCCTGGGCAATGTGCTGGTCTGTGTGCTGGCCCATCACTTTGGCAAAG |

Black lemur | ATGACTTTGCTGAGTGCTGAGGAGAATGCTCATGTCACCTCTCTGTGGGGCAAGGTGGATGTAGAGAAAGTTGGTGGCGAGGCCTTGGGCAGGCTGCTGGTCGTCTACCCATGGACCCAGAGGTTCTTCGAGTCCTTTGGGGACCTGTCCTCTCCTTCTGCTGTTATGGGGAACCCTAAGGTGAAGGCCCATGGCAAGAAGGTGCTGAGTGCCTTTAGTGAAGGTCTGCATCACCTGGACAACCTCAAGGGCACCTTTGCTCAACTGAGTGAGCTGCACTGTGACAAGTTGCACGTGGATCCTCAGAACTTCACTCTCCTGGGCAACGTGCTGGTGGTTGTGCTGGCTGAACACTTTGGCAATGCATTCAGCCCGGCGGTGCAGGCTGCCTTTCAGAAGGTGGTGGCTGGTGTGGCCAATGCTCTGGCTCACAAGTACCACTGA |

Norway rat | ATGGTGCACCTAACTGATGCTGAGAAGGCTACTGTTAGTGGCCTGTGGGGAAAGGTGAATGCTGATAATGTTGGCGCTGAGGCCCTGGGCAGGCTGCTGGTTGTCTACCCTTGGACCCAGAGGTACTTTTCTAAATTTGGGGACCTGTCCTCTGCCTCTGCTATCATGGGTAACCCCCAGGTGAAGGCCCATGGCAAGAAGGTGATAAATGCCTTCAATGATGGCCTGAAACACTTGGACAACCTCAAGGGCACCTTTGCTCATCTGAGTGAACTCCACTGTGACAAGCTGCATGTGGATCCTGAGAACTTCAGGCTCCTGGGCAATATGATTGTGATTGTGTTGGGCCACCACCTGGGCAAGGAATTCACCCCCTGTGCACAGGCTGCCTTCCAGAAGGTGGTGGCTGGAGTGGCCAGTGCCCTGGCTCACAAGTACCACTAA |

House mouse | ATGGTGCACCTGACTGATGCTGAGAAGTCTGCTGTCTCTTGCCTGTGGGCAAAGGTGAACCCCGATGAAGTTGGTGGTGAGGCCCTGGGCAGGCTGCTGGTTGTCTACCCTTGGACCCAGCGGTACTTTGATAGCTTTGGAGACCTATCCTCTGCCTCTGCTATCATGGGTAATCCCAAGGTGAAGGCCCATGGCAAAAAGGTGATAACTGCCTTTAACGAGGGCCTGAAAAACCTGGACAACCTCAAGGGCACCTTTGCCAGCCTCAGTGAGCTCCACTGTGACAAGCTGCATGTGGATCCTGAGAACTTCAGGCTCCTAGGCAATGCGATCGTGATTGTGCTGGGCCACCACCTGGGCAAGGATTTCACCCCTGCTGCACAGGCTGCCTTCCAGAAGGTGGTGGCTGGAGTGGCCACTGCCCTGGCTCACAAGTACCACTAA |

Goat | ATGCTGACTGCTGAGGAGAAGGCTGCCGTCACCGGCTTCTGGGGCAAGGTGAAAGTGGATGAAGTTGGTGCTGAGGCCCTGGGCAGGCTGCTGGTTGTCTACCCCTGGACTCAGAGGTTCTTTGAGCACTTTGGGGACTTGTCCTCTGCTGATGCTGTTATGAACAATGCTAAGGTGAAGGCCCATGGCAAGAAGGTGCTAGACTCCTTTAGTAACGGCATGAAGCATCTTGACGACCTCAAGGGCACCTTTGCTCAGCTGAGTGAGCTGCACTGTGATAAGCTGCACGTGGATCCTGAGAACTTCAAGCTCCTGGGCAACGTGCTGGTGGTTGTGCTGGCTCGCCACCATGGCAGTGAATTCACCCCGCTGCTGCAGGCTGAGTTTCAGAAGGTGGTGGCTGGTGTTGCCAATGCCCTGGCCCACAGATATCACTAA |

Bovine | ATGCTGACTGCTGAGGAGAAGGCTGCCGTCACCGCCTTTTGGGGCAAGGTGAAAGTGGATGAAGTTGGTGGTGAGGCCCTGGGCAGGCTGCTGGTTGTCTACCCCTGGACTCAGAGGTTCTTTGAGTCCTTTGGGGACTTGTCCACTGCTGATGCTGTTATGAACAACCCTAAGGTGAAGGCCCATGGCAAGAAGGTGCTAGATTCCTTTAGTAATGGCATGAAGCATCTCGATGACCTCAAGGGCACCTTTGCTGCGCTGAGTGAGCTGCACTGTGATAAGCTGCATGTGGATCCTGAGAACTTCAAGCTCCTGGGCAACGTGCTAGTGGTTGTGCTGGCTCGCAATTTTGGCAAGGAATTCACCCCGGTGCTGCAGGCTGACTTTCAGAAGGTGGTGGCTGGTGTGGCCAATGCCCTGGCCCACAGATATCATTAA |

Rabbit | ATGGTGCATCTGTCCAGTGAGGAGAAGTCTGCGGTCACTGCCCTGTGGGGCAAGGTGAATGTGGAAGAAGTTGGTGGTGAGGCCCTGGGCAGGCTGCTGGTTGTCTACCCATGGACCCAGAGGTTCTTCGAGTCCTTTGGGGACCTGTCCTCTGCAAATGCTGTTATGAACAATCCTAAGGTGAAGGCTCATGGCAAGAAGGTGCTGGCTGCCTTCAGTGAGGGTCTGAGTCACCTGGACAACCTCAAAGGCACCTTTGCTAAGCTGAGTGAACTGCACTGTGACAAGCTGCACGTGGATCCTGAGAACTTCAGGCTCCTGGGCAACGTGCTGGTTATTGTGCTGTCTCATCATTTTGGCAAAGAATTCACTCCTCAGGTGCAGGCTGCCTATCAGAAGGTGGTGGCTGGTGTGGCCAATGCCCTGGCTCACAAATACCACTGA |

Opossum | ATGGTGCACTTGACTTCTGAGGAGAAGAACTGCATCACTACCATCTGGTCTAAGGTGCAGGTTGACCAGACTGGTGGTGAGGCCCTTGGCAGGATGCTCGTTGTCTACCCCTGGACCACCAGGTTTTTTGGGAGCTTTGGTGATCTGTCCTCTCCTGGCGCTGTCATGTCAAATTCTAAGGTTCAAGCCCATGGTGCTAAGGTGTTGACCTCCTTCGGTGAAGCAGTCAAGCATTTGGACAACCTGAAGGGTACTTATGCCAAGTTGAGTGAGCTCCACTGTGACAAGCTGCATGTGGACCCTGAGAACTTCAAGATGCTGGGGAATATCATTGTGATCTGCCTGGCTGAGCACTTTGGCAAGGATTTTACTCCTGAATGTCAGGTTGCTTGGCAGAAGCTCGTGGCTGGAGTTGCCCATGCCCTGGCCCACAAGTACCACTAA |

| ATGGTGCACTGGACTGCTGAGGAGAAGCAGCTCATCACCGGCCTCTGGGGCAAGGTCAATGTGGCCGAATGTGGGGCCGAAGCCCTGGCCAGGCTGCTGATCGTCTACCCCTGGACCCAGAGGTTCTTTGCGTCCTTTGGGAACCTCTCCAGCCCCACTGCCATCCTTGGCAACCCCATGGTCCGCGCCCACGGCAAGAAAGTGCTCACCTCCTTTGGGGATGCTGTGAAGAACCTGGACAACATCAAGAACACCTTCTCCCAACTGTCCGAACTGCATTGTGACAAGCTGCATGTGGACCCCGAGAACTTCAGGCTCCTGGGTGACATCCTCATCATTGTCCTGGCCGCCCACTTCAGCAAGGACTTCACTCCTGAATGCCAGGCTGCCTGGCAGAAGCTGGTCCGCGTGGTGGCCCATGCCCTGGCTCGCAAGTACCACTAA |

## 3. Similarity analysis of DNA sequence

Let *G* = *g*_{1}, *g*_{2}, *g*_{3}…*g*_{
N
} be an arbitrary complete coding sequence, where *g*_{
i
} ∈ {A, T, G, C} for any *i* ∈ {1, 2,…, *N*}, and *G* = *t*_{1}, *t*_{2}, *t*_{3}…*t*_{
M
} be its corresponding sequence of triplets, where *M* = [*N*/3] and *t*_{
i
} is a triplet of DNA for any *i* ∈ {1, 2,…, *M*}. Then, we define a function *δ* and let *δ* (*t*_{
i
}) represent the total number of times that the triplet *t*_{
i
} repeats in the sequence of triplets *G* = *t*_{1}, *t*_{2}, *t*_{3}…*t*_{
M
} for any *i* ∈ {1, 2,…, *M*}.

Let *T*_{1} = GCT, *T*_{2} = GCC, *T*_{3} = GCA, *T*_{4} = GCG, *T*_{5} = CGT, *T*_{6} = CGC, *T*_{7} = CGA, *T*_{8} = CGG, *T*_{9} = AGA, *T*_{10} = AGG, *T*_{11} = GAT, *T*_{12} = GAC, *T*_{13} = AAT, *T*_{14} = AAC, *T*_{15} = TGT, *T*_{16} = TGC, *T*_{17} = GAA, *T*_{18} = GAG, *T*_{19} = CAA, *T*_{20} = CAG, *T*_{21} = GGT, *T*_{22} = GGC, *T*_{23} = GGA, *T*_{24} = GGG, *T*_{25} = CAT, *T*_{26} = CAC, *T*_{27} = ATT, *T*_{28} = ATC, *T*_{29} = ATA, *T*_{30} = CTT *T*_{31} = CTC, *T*_{32} = CTA, *T*_{33} = CTG, *T*_{34} = TTA, *T*_{35} = TTG, *T*_{36} = AAA, *T*_{37} = AAG, *T*_{38} = TTT, *T*_{39} = TTC, *T*_{40} = CCT, *T*_{41} = CCC, *T*_{42} = CCA, *T*_{43} = CCG, *T*_{44} = TCT, *T*_{45} = TCC, *T*_{46} = TCA, *T*_{47} = TCG, *T*_{48} = AGT, *T*_{49} = AGC, *T*_{50} = ACT, *T*_{51} = ACC, *T*_{52} = ACA, *T*_{53} = ACG, *T*_{54} = TGG, *T*_{55} = TAT, *T*_{56} = TAC, *T*_{57} = GTT, *T*_{58} = GTC, *T*_{59} = GTA, *T*_{60} = GTG, *T*_{61} = ATG, *T*_{62} = TAA, *T*_{63} = TAG, and *T*_{64} = TGA.

Thereafter, according to Table 2, since there are a total of 64 triplets of DNA, then we can construct a set of 64 vectors {<*T*_{1}, *δ* (*T*_{1})>, <*T*_{2}, *δ* (*T*_{2})>,…, <*T*_{64}, *δ* (*T*_{64})>} for the given sequence of triplets *G* = *t*_{1}, *t*_{2}, *t*_{3}…*t*_{
M
} as follows: if *T*_{
i
} = *t*_{
j
} ∈ {*t*_{1}, *t*_{2}, *t*_{3},…*t*_{
M
}}, then *δ* (*T*_{
i
}) = *δ* (*t*_{
j
}), else *δ* (*T*_{
i
}) =0, for any *i* ∈ {1, 2,…, 64} and *j* ∈ {1, 2,…, *M*}.

For convenience, we call {<*T*_{1}, *δ* (*T*_{1})>, <*T*_{2}, *δ* (*T*_{2})>,…, <*T*_{64}, *δ* (*T*_{64})>} as the triplet-repeat model set of *G*.

*A*and

*B*, suppose that their triplet-repeat model sets are {<

*T*

_{1},

*X*

_{1}>, <

*T*

_{2},

*X*

_{2}>,…, <

*T*

_{64},

*X*

_{64}>} and {<

*T*

_{1},

*Y*

_{1}>, <

*T*

_{2},

*Y*

_{2}>,…, <

*T*

_{64},

*Y*

_{64}>}, respectively. Then, on the basis of the 2D graphical representation given in the previous Section 2, we can define the weight deviation between the two DNA sequences

*A*and

*B*as the following formula (2) to measure the similarity between

*A*and

*B*.

*A*and

*B*, the higher the degree of similarity of

*A*and

*B*. According to formula (2), the detailed similarity/dissimilarity matrix obtained for the coding sequences listed in Table 4 is illustrated in Table 5. Basing on the similarity matrix (Table 5) constructs a phylogenetic tree, which is shown in Figure 4.

**The similarity/dissimilarity matrix for the coding sequences of Table**
1
**based on the weight deviation**

Human | Chimpanzee | Gorilla | Lemur | Rat | Mouse | Goat | Bovine | Rabbit | Opossum | Gallus | |
---|---|---|---|---|---|---|---|---|---|---|---|

Human | 0 | 5.2500 | 4.3359 | 8.5891 | 10.670 | 9.7047 | 8.2219 | 8.1438 | 7.8281 | 15.6078 | 16.7109 |

Chimpanzee | 0 | 1.1266 | 8.0297 | 10.645 | 9.6016 | 8.4375 | 9.3219 | 9.6000 | 14.2578 | 15.8734 | |

Gorilla | 0 | 7.8688 | 9.9625 | 8.6063 | 7.6734 | 8.5578 | 8.5547 | 13.9719 | 14.8781 | ||

Lemur | 0 | 8.7219 | 9.5500 | 7.1328 | 9.3891 | 5.6891 | 12.9281 | 15.2000 | |||

Rat | 0 | 6.0750 | 7.0484 | 9.3641 | 9.6578 | 13.5906 | 14.1219 | ||||

Mouse | 0 | 9.4953 | 9.2641 | 10.7984 | 12.3406 | 12.3688 | |||||

Goat | 0 | 5.2625 | 8.7219 | 11.9703 | 14.5359 | ||||||

Bovine | 0 | 9.2906 | 12.5922 | 15.0234 | |||||||

Rabbit | 0 | 14.8984 | 15.6953 | ||||||||

Opossum | 0 | 14.2750 | |||||||||

| 0 |

Observing Table 5, it is easy to find out that human, gorilla, and chimpanzee are most similar to each other, and the pairs like gorilla-chimpanzee (with weight deviation of 1.1266), human-gorilla (with weight deviation of 4.3359), and human-chimpanzee (with weight deviation of 5.2500) are the most similar species pairs, but *Gallus* and opossum are the most dissimilar to the others (with weight deviation bigger than 11). It is consistent with the fact that *Gallus* is not a mammal, whereas the others are mammals, and opossum is the most remote species from the remaining mammals. Similar results have been obtained in other papers by different approaches [2, 5, 7, 9, 33].

**The similarity/dissimilarity of the coding sequences**

Species | A | B | C | D | E |
---|---|---|---|---|---|

Chimpanzee | 5.2500 | 0.0144 | 14.00 | 0.005069 | 0.863 |

Gorilla | 4.3359 | 0.0125 | 13.63 | 0.006611 | 0.339 |

Lemur | 8.5891 | - | 31.75 | 0.030894 | 1.188 |

Rat | 10.670 | 0.1377 | 41.65 | 0.015539 | 1.966 |

Mouse | 9.7047 | 0.1427 | 30.27 | 0.015700 | 0.735 |

Goat | 8.2219 | 0.1161 | 31.39 | 0.020980 | 0.311 |

Bovine | 8.1438 | 0.0773 | 30.68 | 0.017700 | 2.489 |

Rabbit | 7.8281 | 0.1332 | 35.575 | 0.015788 | 1.372 |

Opossum | 15.6078 | - | 48.701 | 0.033363 | 6.322 |

| 16.7109 | - | 70.46 | 0.025801 | 7.170 |

From Table 6, we can find that the pairs like human-gorilla and human-chimpanzee are the two most similar species pairs when adopting (A) the method of our work, (B) the method of [2], (C) the method of [5], and (D) the method of [7], which is in accordance with the fact that gorilla and chimpanzee are the two most closest species of human, but when adopting (E) the method of [9], the most similar species pair is human-goat, which is obviously not correct. In addition, the pairs like human-*Gallus* and human-opossum are the two most dissimilar species pairs when adopting (A) the method of our work, (C) the method of [5], and (E) the method of [9], which is in accordance with the fact that *Gallus* is not a mammal, whereas the others are mammals, and opossum is the most remote species from the remaining mammals. However, when adopting (D) the method of [7], the two most dissimilar species pairs are human-opossum and human-lemur, which is obviously not reasonable also.

## 4. Conclusion

In this paper, we propose a new 2D graphical representation for DNA sequences based on triplets, and associating with a newly introduced concept of weight of triplets and a newly designed measure of similarity named weight deviation, we propose a new method to make similarity analysis of DNA sequences, in which no matrix computation is needed and reasonable and useful approaches for both computational scientists and molecular biologists to effectively analyze DNA sequences can be provided at the same time.

## Declarations

### Acknowledgements

This work is supported by the Chongqing Education Science Project of China in 2014, Chongqing “Twelfth Five Year plan” educational programming projects of China (2013-ZJ-077), program for university youth backbone teachers of Chongqing in 2014.

## Authors’ Affiliations

## References

- Chen W, Liao B, Liu Y, Zhu W, Su Z:
**A numerical representation of DNA sequences and its applications.***MATCH: Commun Math Comput Chem.*2008,**60:**291-300.MathSciNetGoogle Scholar - Jafarzadeh N, Iranmanesh A:
**A novel graphical and numerical representation for analyzing DNA sequences based on codons.***MATCH: Commun Math Comput Chem.*2012,**68:**611-620.MathSciNetGoogle Scholar - Liao B, Liao BY, Sun XM, Zeng QG:
**A novel method for similarity analysis and protein sub-cellular localization prediction.***Bioinformatics*2010,**26:**2678-2683. 10.1093/bioinformatics/btq521View ArticleGoogle Scholar - Qi XQ, Wu Q, Zhang Y, Fuller E, Zhang CQ:
**A novel model for DNA sequence similarity analysis based on graph theory.***J Evol Bioinform*2011,**7:**149-158.Google Scholar - Yu JF, Wang JH, Sun X:
**Analysis of similarities/dissimilarities of DNA sequences based on a novel graphical representation.***MATCH: Commun Math Comput Chem.*2010,**63:**493-512.MathSciNetGoogle Scholar - Li Y, Huang G, Liao B, Liu Z:
**H-L curve: a novel 2D graphical representation of protein sequences.***MATCH: Commun Math Comput Chem.*2009,**61:**519-532.MathSciNetGoogle Scholar - Liao B, Wang TM:
**New 2D graphical representation of DNA sequences.***J. Comput. Chem.*2004,**25:**1364-1368. 10.1002/jcc.20060View ArticleGoogle Scholar - Liao B, Xiang XY, Zhu W:
**Coronavirus phylogeny based on 2D graphical representation of DNA sequence.***J. Comput. Chem.*2006,**27:**1196-1202. 10.1002/jcc.20439View ArticleGoogle Scholar - Liu ZB, Liao B, Zhu W, Huang GH:
**A 2D graphical representation of DNA sequence based on dual nucleotides and its application.***Int. J. Quantum Chem.*2009,**109:**948-958. 10.1002/qua.21919View ArticleGoogle Scholar - Randic M, Vracko M, Zupan J, Novic M:
**Compact 2D graphical representation of DNA.***Chem. Phys. Lett.*2003,**373:**558-562. 10.1016/S0009-2614(03)00639-0View ArticleGoogle Scholar - Randic M, Vracko M, Lers N, Plavsic D:
**Analysis of similarity/dissimilarity of 2D graphical representation.***Chem. Phys. Lett.*2003,**371:**202-207. 10.1016/S0009-2614(03)00244-6View ArticleGoogle Scholar - Randic M, Vracko M, Lers N, Plavsic D:
**Novel 2-D graphical representation of DNA sequences and their numerical characterization.***Chem. Phys. Lett.*2003,**368:**1-6. 10.1016/S0009-2614(02)01784-0View ArticleGoogle Scholar - Randic M:
**Graphical representations of DNA as 2-D map.***Chem. Phys. Lett.*2004,**386:**468-471. 10.1016/j.cplett.2004.01.088View ArticleGoogle Scholar - Guo XF, Randic M, Basak SC:
**A novel 2-D graphical representation of DNA sequences of low degeneracy.***Chem. Phys. Lett.*2001,**350:**106-112. 10.1016/S0009-2614(01)01246-5View ArticleGoogle Scholar - Guo XF, Nandy A:
**Numerical characterization of DNA sequences in a 2-D graphical representation scheme of low degeneracy.***Chem. Phys. Lett.*2003,**369:**361-366. 10.1016/S0009-2614(02)02029-8View ArticleGoogle Scholar - Qi ZH, Qi XQ:
**Novel 2D graphical representation of DNA sequence based on dual nucleotides.***Chem Phys Lett.*2007,**440:**139-144. 10.1016/j.cplett.2007.03.107View ArticleGoogle Scholar - Dai Q, Xiu ZL, Wang TM:
**A novel 2D graphical representation of DNA sequences and its application.***J Mol Graph Model.*2006,**25:**340-344. 10.1016/j.jmgm.2005.12.004View ArticleGoogle Scholar - Liu XQ, Dai Q, Xiu ZL, Wang TM:
**PNN–curve: a new 2D graphical representation of DNA sequences and its application.***J. Theor. Biol.*2006,**243:**555-561. 10.1016/j.jtbi.2006.07.018MathSciNetView ArticleGoogle Scholar - Dorota BW, Timothy C, Piotr W:
**2D-dynamic representation of DNA sequences.***Chem. Phys. Lett.*2007,**442:**140-144. 10.1016/j.cplett.2007.05.050View ArticleGoogle Scholar - Yuan CX, Liao B, Wang TM:
**New 3D graphical representation of DNA sequences and their numerical characterization.***Chem. Phys. Lett.*2003,**379:**412-417. 10.1016/j.cplett.2003.07.023View ArticleGoogle Scholar - Liao B, Wang TM:
**3-D graphical representation of DNA sequences and their numerical characterization.***J. Mol. Struct. (THEOCHEM)*2004,**681:**209-212. 10.1016/j.theochem.2004.05.020View ArticleGoogle Scholar - Liao B, Wang TM:
**A 3D graphical representation of RNA secondary structure.***J Biomol Struct Dynam.*2004,**21:**827-832. 10.1080/07391102.2004.10506972MathSciNetView ArticleGoogle Scholar - Cao Z, Liao B, Li RF:
**A group of 3D graphical representation of DNA sequences based on dual nucleotides.***Int. J. Quantum Chem.*2008,**108:**1485-1490. 10.1002/qua.21698View ArticleGoogle Scholar - Randic M, Vracko M, Nandy A, Basak SC:
**On 3D graphical representation of DNA primary sequences and their numerical characterization.***J. Chem. Inf. Comput. Sci.*2000,**40:**1235-1244. 10.1021/ci000034qView ArticleGoogle Scholar - Randic M, Zupan J, Novic M:
**On 3D graphical representation of proteomics maps and their numerical characterization.***J. Chem. Inf. Comput. Sci.*2001,**41:**1339-1344. 10.1021/ci0001684View ArticleGoogle Scholar - Qi XQ, Fan TR:
**PN-curve: a 3D graphical representation of DNA sequences and their numerical characterization.***Chem. Phys. Lett.*2007,**442:**434-440. 10.1016/j.cplett.2007.06.029View ArticleGoogle Scholar - Yu JF, Sun X, Wang JH:
**TN curve: a novel 3D graphical representation of DNA sequence based on trinucleotides and its applications.***J. Theor. Biol.*2009,**261:**459-468. 10.1016/j.jtbi.2009.08.005View ArticleGoogle Scholar - Aram V, Iranmanesh A:
**3D-dynamic representation of DNA sequences.***MATCH: Commun Math Comput Chem.*2012,**67:**809-816.MathSciNetGoogle Scholar - Liao B, Tan MS, Ding KQ:
**A 4D representation of DNA sequences and its application.***Chem. Phys. Lett.*2005,**402:**380-383. 10.1016/j.cplett.2004.12.062View ArticleGoogle Scholar - Tang XC, Zhou PP, Qiu WY:
**On the similarity/dissimilarity of DNA sequences based on 4D graphical representation.***Chin. Sci. Bull.*2010,**55:**701-704. 10.1007/s11434-010-0045-2View ArticleGoogle Scholar - Chi R, Ding KQ:
**Novel 4D numerical representation of DNA sequences.***Chem. Phys. Lett.*2005,**407:**63-67. 10.1016/j.cplett.2005.03.056View ArticleGoogle Scholar - Liao B, Xiang XY, Li RF, Zhu W:
**On the similarity of DNA primary sequences based on 5D representation.***J. Math. Chem.*2007,**42:**47-57. 10.1007/s10910-006-9091-zMathSciNetView ArticleGoogle Scholar - He P, Wang J:
**Characteristic sequences for DNA primary sequence.***J. Chem. Inf. Comput. Sci.*2002,**42:**1080-1085. 10.1021/ci010131zView ArticleGoogle Scholar

## Copyright

This article is published under license to BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.