The X chromosomes of mammals: karyological homology as revealed by banding techniques

Abstract

A comparison of the Giemsa banding patterns of the X chromosomes in various mammalian species including man indicates that two major bands (A and B), which are resistant to trypsin and urea treatments, are always present irrespective of the gross morphology of the X chromosomes. This is true in all mammalian species with the 'original or standard type' X chromosomes (5-6% of the haploid genome) thus far analyzed. In the unusually large sized X chromosomes the extra chromosomal material may be due either to the addition of genetically inert constitutive heterochromatin or to an X autosome translocation. In these X chromosomes two major bands are present in the actual X chromosome segment. These data on C and G band patterns also support Ohno's hypothesis that the mammalian X chromosome is extremely conservative in its genetic content, in spite of its cytogenetic variability.