The disaster at the Chernobyl Nuclear Power Plant in April 1986 was accompanied by the release of large amounts of radioisotopes, resulting in the contamination of extensive regions of the Ukraine, Byelorus and the Russian Federation. Cleanup workers (liquidators) and people living on land contaminated with radioactive materials were most exposed. To assess the genetic effects of exposure to ionizing radiation after the Chernobyl accident, we have measured the frequency of inherited mutant alleles at seven hypermutable minisatellite loci in 183 children born to Chernobyl cleanup workers (liquidators) and 163 children born to control families living in nonirradiated areas of the Ukraine. There was no significant difference in the frequency of inherited mutant alleles between the exposed and control groups. The exposed group was then divided into two subgroups according to the time at which the children were conceived with respect to the fathers' work at the power plant. Eighty-eight children were conceived either while their fathers were working at the facility or up to 2 months later (Subgroup 1). The other 95 children were conceived at least 4 months after their fathers had stopped working at the Chernobyl site (Subgroup 2). The frequencies of mutant alleles were higher for the majority of loci (i.e. 1.44 times higher for CEB1) in Subgroup 1 than in Subgroup 2. This result, if confirmed, would reconcile the apparently conflicting results obtained in the chronically exposed Byelorus population and the Hiroshima-Nagasaki A-bomb survivors.

We report a deletion of lp36.3 in a child with microcephaly, mental retardation, broad forehead, deep set eyes, depressed nasal bridge, flat midface, relative prognathism, and abnormal ears. The phenotype is consistent with that described for partial monosomy We now report the results of analysing our sample with one more HVP from the terminal region of chromosome lp. We have detected a chromosomal deletion of lp that was not apparent on routine cytogenetic testing in a child with developmental delay and congenital anomalies. Further analysis with lp probes, reverse painting, and FISH with telomere specific cosmids suggests that the child has a pure monosomy of the terminal 5-7 megabases (Mb) of lp. Materials and methods DNA ANALYSISVenous blood samples were taken from the patient and both parents. Epstein-Barr virus transformed lymphoblast cultures were established (available on request to JF). DNA was extracted from cell lines and peripheral blood by standard procedures.3 Samples from both parents and the affected offspring were digested with an appropriate restriction endonuclease, electrophoresed through 0.8% agarose gels, transferred to nylon membranes, and hybridised to radioactively labelled probes.3 PROBES AND GENETIC MAPPING Minisatellites used in this report are listed in table 1 and were cloned using the approach previously described4 ' and unpublished procedures. The cosmid containing CEB 108 and the chromosome 1 cosmid for D1F101S2 are derived from the ICRF chromosome 1 cosmid library. All the others are derived from a commercial library.4The minisatellite loci have been genetically mapped by typing of 40 CEPH families and heterozygosity estimated from 80 CEPH parents. The sex average distance from the lp telomere is deduced from our unpublished data at two more distal minisatellite loci (D1F35S2 and D1F102S1) and computed using CRIMAP version 2.4. All genotyping data are available from CEPH database version 8.1

We have developed approaches for the cloning of minisatellites from total genomic libraries and applied these approaches to the human, rat, and pig genomes. The chromosomal distribution of minisatellites in the three genomes is strikingly different, with clustering at chromosome ends in human, a seemingly almost even distribution in rat, and an intermediate situation in pig. A closer analysis, however, reveals that interstitial sites in pig and rat often correspond to terminal cytogenetic bands in human. This observation suggests that minisatellites are created toward chromosome ends and their internalization represents secondary events resulting from rearrangements involving chromosome ends.

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