The distribution of genes on chromosomes: A cytological approach

Abstract

Studies during the last 20 years have shown that the chromosomes of many organisms, especially those of higher vertebrates, consist of a series of segments having different properties. These can be recognized as, for example, G- and R-bands. Recent studies have indicated that genes tend to lie in the R-bands rather than in the G-bands, although the number of genes that has been mapped with high precision is, as yet, only a very small proportion of the total, probably much less than 1%. We have therefore sought to study the distribution of genes on chromosomes using a cytological approach in conjunction with "universal" markers for genes. Such markers include mRNA and the gene-rich, G+C-rich H3 fraction of DNA, both of which can be localized using in situ hybridization, and DNase I hypersensitivity, and digestion by restriction enzymes known to show selectivity for the CpG islands associated with active genes, both of which can be detected using in situ nick translation. We have chosen to use the approaches involving in situ nick translation and have shown that the patterns of DNase I hypersensitivity and of CpG islands on human chromosomes show a strict correspondence to R-banding patterns: Deviations from R-banding patterns reported by previous investigators who have made similar studies appear to be attributable to excessive digestion.(ABSTRACT TRUNCATED AT 250 WORDS)

Exposure to low concentrations of etoposide reduces the apoptotic capability of leukaemic cell lines

“…36 In contrast to the more indiscriminate damage caused by cisplatin, the DNA sequence specificity of topo II ensures the existence of favourable sites in DNA to which etoposide and doxorubicin can interact and cause anomalies. Importantly, these preferred sites tend to traverse regions that are rich in genes, 37 and as a result, topo II inhibitor/DNA interactions can potentially affect many genes. 6 Studies have demonstrated an association between DNA topo II cleavage sites and translocation breakpoints/aberrations, 38,39 suggesting that translocation mechanisms may involve DNA topo II-mediated chromosomal breakage before formation of translocations when the breakage is repaired.…”

Rapid development of PCR-based genome-specific repetitive DNA junction markers in wheat

“…Therefore, markers derived from gene sequences are usually unevenly distributed along the chromosomes. In addition, most eukaryotic genomes are often organized in gene-rich regions separated by gene-poor regions (Sumner et al 1993). Sequence analyses of largeinsert wheat BAC clones and random shotgun sequences revealed that repeat DNA, accounting for over 80% of the genome, is present in genic and intergenic regions (Wicker et al 2001(Wicker et al , 2003bSanMiguel et al 2002;Li et al 2004;Paux et al 2006;Gu et al 2006).…”

Distribution of genes and recombination in wheat and other eukaryotes

“…Uneven distribution of genes on chromosomes seems to be a common feature of all eukaryotes (Sumner et al, 1993;Lichten and Goldman, 1995). Even in the eukaryote with the smallest genome, S. cerevisiae, gene-density among regions may vary more than 2-fold (Dujon et al, 1997).…”