The chromosome complement of Olea europaea L.: characterization by differential staining of the chromatin and in-situ hybridization of highly repeated DNA sequences.

The chromosome complement of olive (Olea europaea L.) has been characterized by differential staining of the chromatin and chromosomal localization of highly repeated DNA sequences and ribosomal cistrons. DAPI staining produces different-sized positive bands in various locations on all the chromosomes. By combining this band pattern with the results obtained from cytological hybridization of OeTaq80, OeTaq178, and OeGEM86 DNA tandem repeats, most of the pairs can be distinguished from each other, in spite of the large number of chromosomes (2n = 46), their small size and similar morphology. Different tandem-repeated DNA sequences may be contained into single heterochromatic chromosome regions, even though there are regions where repeats of only one family are present. OeTaq80- and OeGEM86-related DNA sequences are rather specific to the heterochromatin at the chromosome ends, while most sequences related to the longer OeTaq178 probe are confined to interstitial heterochromatin. Some exceptions suggest that major chromosomal rearrangements occurred during genome evolution. Polymorphism, which may differentiate olive cultivars, was observed within chromosome pairs I, V, and VII.