C-heterochromatin polymorphism in Baetica ustulata: intraindividual variation and fluorescence banding patterns

Abstract

In an attempt to determine the nature and extent of the extensive C-banding heterochromatin variation found in the monospecific genus Baetica, 52 individuals were analysed by C-banding and fluorescence methods. The use of fluorescent DNA-binding dyes with different specificities allowed us to distinguish three major categories of constitutive C-heterochromatin. Two of these correspond to AT-rich and GC-rich DNA; the third shows no fluorescence with any of the fluorochromes employed. Apart from confirming polymorphisms for C-band patterns in the medium-sized autosomes, several C-banding variants (cytotypes) were found in the two testes of one individual. From a comparative study of these cytotypes we deduce that equal or unequal sister chromatid exchanges, as well as mitotic crossovers, operating during the early germ line divisions have been the major mechanisms responsible for this intraindividual variation. Because of the high level of C-band polymorphism found in this species, it seems reasonable to argue that, for unknown reasons, certain processes that normally occur over generations have occurred repeatedly in this abnormal individual.