RIBOSOMAL GENE NUMBER IN INDIVIDUAL HUMAN GENOMES - DATA FROM COMPARATIVE MOLECULAR AND CYTOGENETIC ANALYSIS

Methods were elaborated for determining the relative and absolute quan tities of genomic DNA repeated sequences. Thereby the copy number of t he sequence tested could be differentiated in the samples under study even if the difference was only 5-10%. Methods are based on dot and bl ot hybridization of a photobiotinylated probe with genomic DNA and spe ctrophotometric determination of the amount of the dye eluted from the colored complex. The relative amount of ribosomal genes (RG) was dete rmined in genomic DNA of karyotypically normal healthy persons for who m the content of active and silent RG in each of 10 nucleolus organize r regions (NORs) of metaphase chromosomes had been earlier determined by cytogenetic methods, e.g., by specific staining of clusters of acti ve RG by silver nitrate (AgNOR) and in situ hybridization with a label ed rDNA probe. A linear correlation between the RG copy number determi ned by molecular and cytogenetic methods was found in a group of nine patients. It may be suggested that the visual method of determining th e AgNOR size elaborated by cytogeneticists really does reflect the num ber of RG copies in individual NORs and in genomes in tote, and that i t may be recommended for comparing the RG copy number in individual ge nomes of humans. More accurate data on the number of RG in human genom e were obtained: the G1-diploid nucleus of human cells was shown to ca rry, on average, 485 ribosomal genes. In individual genomes the RG cop y number varied from 390 to 580 copies.