Classification of genes, rearrangements and chromosomes according to the chromosome field

Abstract

The study of over 700 species, from algae to humans, reveals that specific DNA sequences, have an optimal territory within the centromere‐telomere field. These DNA sequences have maintained their territory within the chromosome field for millions of years irrespective of variation in arm length, of change in chromosome type and of species evolution. Some of these DNA sequences have been isolated biochemically or analysed at the molecular level. They include, e.g., the proximal heterochromatic segments, the genes for ribosomal RNA, and the telomeric heterochromatin. Order prevails in the eukaryotic chromosome. This order allows classification of genes, rearrangements and chromosomes on a genetic basis. Genes are classified as centrons, medons and telons. Rearrangements are classified as: conservative, discordant, disruptive, destructive and incompatible. Chromosomes are also classified depending on their length, arm size and number. These chromosome properties and features now acquire an organizatory meaning which they lacked previously. The available molecular information supports the evidence from the field. The study of the split gene reveals that it is the relative position of the DNA sequences which determines their function. On the basis of the chromosome field, predictions can be made concerning gene organization, gene function and chromosome evolution.

Distribution of 5S and 45S rDNA sites in plants with holokinetic chromosomes and the “chromosome field” hypothesis

“…Therefore, the distribution of these sites is not influenced by the centromere-telomere polarization, as assumed in the "chromosome field" hypothesis (Lima-de-Faria, 1976, 1980. The predominant localization of these sites in the terminal regions of the chromosomes is more probably related to the high frequency of inter-locus rearrangements in tandem repeated sequences (Skalická et al, 2003).…”

“…In species with monocentric chromosomes, the presence of the centromere would define a field having the centromere on one side and the telomere on the other. In this field, which corresponds to a chromosome arm, certain phenomena such as the position of the chiasmata and the NORs occur non-randomly (Lima-de-Faria, 1976, 1980. Therefore, the existence of a "chromosome field" should depend on the occurrence of a localized centromere and should be restricted to monocentric chromosomes only.…”

Cytological studies onPrimulinataxa (Gesneriaceae) from limestone karsts in Guangxi province, China

“…Apart from eight confirmatory counts and one new somatic chromosome number for previously investigated species, all other counts are reported here for the first time. Chromosomes in Primulina are small in size according to the classification of Lima-de-faria (1980), with a range of 0.6 to 2.4 μm, showing only slight size variation. Frequently, one or two satellites were observed in the 18 taxa studied.…”

Genomic characterisation of Arachis porphyrocalyx (Valls & C.E. Simpson, 2005) (Leguminosae): multiple origin of Arachis species with x = 9

“…These data do not agree with those reported by Peñaloza and Valls (2005) who observed four pairs of submetacentric chromosomes, but this discrepancy can be due to the fact that the formula published by these authors is based only on a visual analysis. Chromosomal size ranged between 1.24 and 2.08 µm with a mean length of 1.63 µm, belonging to the category of small chromosomes according to Lima de Faría (1980), and the mean length of diploid complement was 29.37 µm (Table 1). The indexes of asymmetry revealed a moderately high degree of intrachromosomal asymmetry (A1 = 0.30) but low interchromosomal asymmetry (A2 = 0.16).…”