We calculated nucleotide distribution curves along the DNA molecules of the human chromosomes 21 and 22, their correlations in more than 10,000 equidistant positions, and subjected the correlations to cluster analysis. The cluster analysis demonstrated that both DNA molecules were composed of two types of segments exhibiting qualitatively different correlations. The segments differed most in the correlation of the distribution curves of cytosine and guanine, which was very high in type I segments but weak in type II segments. The type I and II segments also significantly differed in the correlations of the distribution curves of adenine with thymine. In addition, adenine strongly anticorrelated with cytosine but this anticorrelation was uniform along both chromosomes and, therefore, it did not contribute to the distinction of the two types of segments. The segments were up to 100 kbp long but they had nothing in common with isochores. Building blocks of the mosaic structure of the DNA molecules of the human chromosomes 21 and 22 are very similar but different in several interesting aspects from those of E. coli.

• MeSH
• DNA bakterií chemie   MeSH
• DNA chemie   MeSH
• Escherichia coli genetika   MeSH
• konformace nukleové kyseliny MeSH
• lidé MeSH
• lidské chromozomy, pár 21 * MeSH
• lidské chromozomy, pár 22 * MeSH
• repetitivní sekvence nukleových kyselin MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA bakterií MeSH
• DNA MeSH

We analyzed occurrences of bases in 20,352 introns, exons of 25,574 protein-coding genes, and among the three codon positions in the protein-coding sequences. The nucleotide sequences originated from the whole spectrum of organisms from bacteria to primates. The analysis revealed the following: (1) In most exons, adenine dominates over thymine. In other words, adenine and thymine are distributed in an asymmetric way between the exon and the complementary strand, and the coding sequence is mostly located in the adenine-rich strand. (2) Thymine dominates over adenine not only in the strand complementary to the exon but also in introns. (3) A general bias is further revealed in the distribution of adenine and thymine among the three codon positions in the exons, where adenine dominates over thymine in the second and mainly the first codon position while the reverse holds in the third codon position. The product (A1/T1)x(A2/T2)x(T3/A3) is smaller than one in only a few analyzed genes.

• MeSH
• adenin analýza   MeSH
• DNA chemie   genetika   MeSH
• eukaryotické buňky MeSH
• exony genetika   MeSH
• genetický kód MeSH
• genom MeSH
• geny genetika   MeSH
• introny genetika   MeSH
• nukleové kyseliny chemie   genetika   MeSH
• prokaryotické buňky MeSH
• RNA chemie   genetika   MeSH
• thymin analýza   MeSH
• zastoupení bazí * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• srovnávací studie MeSH
• Názvy látek
• adenin MeSH
• DNA MeSH
• nukleové kyseliny MeSH
• RNA MeSH
• thymin MeSH