[Comparative analysis on content and distribution of CpG sites in milk production traits and mastitis-related genes in dairy cattle].

DNA methylation is a major part of epigenetics. DNA methylation on the CpG sites in gene promoter and the first exon often represses gene expression, but demethylation activates gene expression. Previous research has shown that a negative correlation was found between mastitis index (somatic cell count, SCC) and milk production traits in Holsteins. The content and distribution of CpG dinucleotide sites in different regions of the candidate genes related to milk production traits and mastitis were studied in the present study. The regions contained promoter (2000 bp upstream of transcriptional start site), exon 1, and 2000 bp downstream of transcriptional end site. The CpG number of promoter and exon 1 in the mastitis-related genes was significantly less than that of the milk production-associated genes. However, the CpG number of 2000 bp downstream of the genes for the two traits was not significantly different. Two new index quantified CpG characterizations were proposed. One is the CpG distance, which can measure the distribution of CpG. The other is the conditional probability p(G|C), which is used to quantify the probability of CpG in a nucleotide sequence along with C. The two indexes of promoter and exon 1 in the two types of genes and their statistic analysis were carried out. This study sets the basis for DNA methylation regulation of milk production traits- and mastitis-related genes.

Protein sequence analysis based on hydropathy profile of amino acids.

Biology sequence comparison is a fundamental task in computational biology. According to the hydropathy profile of amino acids, a protein sequence is taken as a string with three letters. Three curves of the new protein sequence were defined to describe the protein sequence. A new method to analyze the similarity/dissimilarity of protein sequence was proposed based on the conditional probability of the protein sequence. Finally, the protein sequences of ND6 (NADH dehydrogenase subunit 6) protein of eight species were taken as an example to illustrate the new approach. The results demonstrated that the method is convenient and efficient.

[A new alignment-free sequence analysis based on the distribution of K-tuple].

Based on the distribution of K-tuple in complete genome, a method without doing sequence alignment to infer difference of biological sequence is proposed in this paper. The method can be used to measure the difference of distribution on K-tuple between the native DNA sequences and the corresponding randomized ones. Applied to construct phylogenetic trees of the complete mitochondrial genomes of 26 species of placental mammals, with K increasing, it yields phylogenetic trees of which the classification effect increasingly matches the result widely recognised by the biological field. The final results show that the phylogenetic trees built by this method is more reasonable than by other alignment-free sequence methods.

[Maximum entropy principle and population genetic equilibrium].

A general mathematic model of population genetic equilibrium was constructed based on the maximum entropy principle. We proved that the maximum entropy probability distribution was equivalent to the Hardy-Weinberg equilibrium law. A population reached genetic equilibrium when the genotype entropy of the population reached the maximal possible value. In information theory, the entropy or the information content is used to measure the uncertainty of a system. In population genetics, we can use entropy to measure the uncertainty of the genotype of a population. The agreement of the maximum entropy principle and the hardy-Weinberg equilibrium law indicated that random crossing is an irreversible process, which increases the genotype entropy of the population, while inbreeding and selection decrease the genotype entropy of the population. In animal or plant breeding, we often use selection and/or inbreeding to decrease the entropy of a population, and use intercrossing to increase the entropy of the population. In this point of view, breeding is actually regulating the entropy of population. By applying the basic principle of informatics in population genetics, we revealed the biological significance of the genotype entropy and demonstrated that we can work over population genetic problems with the principles and methods of informatics and cybernetics.