To identify sequences from the centromeric region, we have constructed a Drosophila melanogaster yeast artificial chromosome (YAC) library and screened it with purified DNA from the minichromosome Dp(l;f)1187 derived from the X chromosome. We describe the structure ofone clone isolated in this way. This YAC is structurally unstable and contains tandemly repeated G+C-rich li-mer and 12-mer units, which we call dodeca satellite. Most of this satellite is located near the centromere of an autosome. Cross-hybridizing sequences are found in the genomes of organisns as distant as Arabidopsis thaliana and Homo sapiens.A total of 11 simple repeated sequences have been cloned from gradient-purified satellite DNA ofD. melanogaster and the nucleotide sequence ofeach repeat conforms to a formula (RRN)m(RN),,, where R is A or G and N is any nucleotide (8).In this study, we have developed an approach to the cloning of centromeric heterochromatin sequences from D. melanogaster. Thus, we have discovered a type of tandemly repeated DNA sequence that is located in the centromeric region of some D. melanogaster chromosomes and that cross-hybridizes with DNA from other species including Arabidopsis and humans.** The genomes of higher eukaryotes contain large amounts of simple and complex tandemly repeated DNA sequences, classically termed satellite DNA (for review, see ref.

We have studied a girl, her sister and her mother who had a supernumerary marker chromosome in mosaicism. The marker was studied by cytogenetic methods and non-isotopic in situ hybridization with the single D22S9 DNA probe which maps to 22q11. The supernumerary chromosome was derived from a chromosome 22 and it did not present the same morphology in all the cells. At least 5 distinct types of the marker chromosome were detected and some of them were probably derived from each other (dynamic mosaicism). The proposita had an MCA pattern consistent with mild cat eye syndrome, while her sister and her mother had some of the manifestations described in this syndrome. A specific correlation could be established between phenotype and karyotype.

No abstract

Fixed chromosomes of Baetica ustulata were treated with restriction endonucleases and subsequently stained with either Giemsa or the DNA-specific dye propidium iodide. Each enzyme produces a specific banding pattern with both dyes, which demonstrates the value of restriction endonucleases for chromosome banding in this species. The results obtained agree with the hypothesis that the action of restriction enzymes is based on cutting and extraction of DNA and is essentially determined by DNA base composition rather than by chromatin structure. However, strictly centric bands could be an exception. At least nine chromatin types can be distinguished in B. ustulata according to their different response to enzyme digestion and to the fluorescence banding patterns. Differential digestion of specific heterochromatic areas in band 4.4 and in the supernumerary segment of M5 by the HpaII – MspI enzyme pair suggests a high level of DNA methylation at these regions. The distribution of the different classes of DNA repeated sequences in the chromosome complement of B. ustulata indicates that some bands seem to follow the general principles of heterochromatin equilocality, while conceited evolution of heterochromatic DNA in other regions might have different rates of convergence in this species.Key words: restriction endonucleases, chromatin heterogeneity, methylated bands, equilocality, concerted evolution.