We describe here the results of a search of Mendelian inheritance in man, GENDIAG and other sources which suggest that, in comparison with autosomes 1, 2, 3, 4 and 11, the X chromosome may contain a significantly higher number of sex- and reproduction-related (SRR) genes. A similar comparison between X-linked entries and a subset of randomly chosen entries from the remaining autosomes also indicates an excess of genes on the X chromosome with one or more mutations affecting sex determination (e.g. DAX1), sexual differentiation (e.g. androgen receptor) or reproduction (e.g. POF1). A possible reason for disproportionate occurrence of such genes on the X chromosome could be that, during evolution, the 'choice' of a particular pair of homomorphic chromosomes for specialization as sex chromosomes may be related to the number of such genes initially present in it or, since sex determination and sexual dimorphism are often gene dose-dependent processes, the number of such genes necessary to be regulated in a dose-dependent manner. Further analysis of these data shows that XAR, the region which has been added on to the short arm of the X chromosome subsequent to eutherian-marsupial divergence, has nearly as high a proportion of SRR genes as XCR, the conserved region of the X chromosome. These observations are consistent with current hypotheses on the evolution of sexually antagonistic traits on sex chromosomes and suggest that both XCR and XAR may have accumulated SRR traits relatively rapidly because of X linkage.
We have reported that production and characterization of antibodies highly specific to 5-methyl-cytosine (SmC) and the development of a sensitive immunochemicai method for the detection of 5mC in DNA [EBBS Lett. (1982) 150, 4691. Extension of this method to two other modified bases, 6-m~hyladenine (6mA) and %methyiguanine (7mG), is reported here. By use of this immunochemical approach, we are able to detect 5mC, 6mA and 7mG in human and Drosophila DNA and confirm their presence in the DNA of two mealybug species.
DNA methylation Biotin-avidin cross-linking DNA-protein interaction Z-DNA X-chromosome inactivationGene regulation
We have previously reported a sensitive immunochemical method for detecting 5‐methylcytosine in DNA which involves spotting DNA samples on nitrocellulose paper and detection of 5‐methylcytosine, if any, by a combination of the double antibody method and a staining reaction brought about by biotin‐avidin and peroxidase. We report here a linear relationship between the concentration of 5‐methylcytosine in DNA and staining intensity, as recorded by photoacoustic spectroscopy. It appears possible to obtain, by this method, reliable quantitative estimates of 5‐methylcytosine in nanogram quantities of intact DNA. When Drosophila melanogaster DNA was assayed for the presence of 5‐methylcytosine by this method, a faint but clearly positive reaction was obtained. When the photoacoustic intensity of this stained spot is compared with a calibration plot derived from phi X174 DNA whose 5‐methylcytosine content is known, we obtain, for D. melanogaster DNA, one 5‐methylcytosine residue in approximately 12 500 bases or 0.008 mol% methylation.
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