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We investigated the reliability of chorionic villous biopsy as a method to obtain tissues reflecting the genetic constitution of the embryo. In 12 pregnancies before elective termination, we searched for detectable maternal tissue after careful dissection of villi from small 2-5-mg specimens that yielded 7 micrograms of DNA per mg tissue. In Southern blotting experiments (1-2 micrograms DNA per lane), restriction fragment length polymorphisms (RFLPs) at an autosomal (D14S1) and a sex chromosomal (DXYS1) locus allowed recognition of maternally and embryonically derived alleles. Pure villi were obtained in six of the seven informative cases. One biopsy was not dissected satisfactorily; a mixture of embryonic and maternal DNA was found. Nonvillous tissues were mostly maternally derived in eight informative cases. Sex determination by molecular analysis (alleles at the DXYS1 locus) agreed with the karyotypes of uncultured or cultured villi. In one continuing pregnancy, distinct RFLPs indicated maternal inheritance of the alpha-thalassemia 1 trait in a female embryo without detectable maternal contamination. Reliable prenatal diagnosis depends on the specimen's purity. Maternal contamination can be evaluated by DNA analyses.

Three cloned single copy sequences isolated from a random partial plasmid library of human EcoRI-HindIII restriction fragments detect MspI site polymorphisms in human DNA. Since at least two of them have allele frequencies that make them suitable for family linkage studies, we have determined their chromosomal localizations. DNA samples extracted from a panel of 31 Chinese hamster x human somatic cell hybrids, that were derived from six different human donors, were analyzed for the presence of human EcoRI or HindIII fragments hybridizing with the three probes. The results were correlated with the human chromosome contents of the hybrids. Concordancy was observed for clone pMS 1-14 (preliminary locus designation DOSLC3) and human chromosome 15, for clone pMS 1-27 (DOSLC2) and chromosome 20, and for clone pMS 1-37 (DOSLC1) and chromosome 3. Two independent hybrids had retained only the long arm of chromosome 3 and did not hybridize with this probe. Therefore, we assign this locus (now termed D3S3) to the short arm of chromosome 3.

Hybridization of probe pDP151 (locus D15S2) to genomic human DNAs digested with EcoRI revealed allelic restriction fragments 9 and 11 kilobase-pairs (kb) in length. Hybridization of pDP151 to EcoRI-digested DNAs from 21 Chinese hamster X human hybrid cell clones containing different subsets of human chromosomes demonstrated cosegregation of the 9 and 11 kb EcoRI fragments with human chromosome 15. D15S2 and two other polymorphic loci previously mapped to chromosome 15--D15S1 and D15S6--were localized to specific regions on human chromosome 15. Eight Chinese hamster X human somatic cell hybrid clones derived from a human donor heterozygous for a balanced translocation between chromosomes 15 and 22 [t(15;22)(q14;q13.3); Oliver et al, Cytogenet Cell Genet 22:503-510, 1978] were studied. After digestion of human and hybrid DNAs with HindIII and Southern blotting, pDP151 (D15S2) and pMS1-14 (D15S1) hybridized to fragments of 4 and 4.5 kb, respectively. Further, pMS1-14 (D15S1) and p9-1a (D15S6) hybridized to EcoRI fragments of 3.5 and 3.2 kb. All fragments cosegregated with the der(22) derivative chromosome containing region 15q14----15qter. In situ hybridization of these probes to normal human chromosomes mapped the corresponding loci with greater precision: D15S1 to 15q15----15q21, D15S2 to 15q15----15q22, and D15S6 to 15q22----15q24.

We have isolated cDNA clones complementary to a c-Ki-ras cellular oncogene that is amplified in Y1 mouse adrenal tumor cells, with the amplified sequences located on double-minute chromatin bodies (DMs) and homogeneously staining chromosomal regions (HSRs). Characterization of the cDNAs included the isolation of corresponding genomic clones, Northern blot analysis of RNA, and DNA sequence analysis. Our studies demonstrate that the c-Ki-ras gene amplified in the Y1 cells is homologous to the human c-Ki-ras2 gene. We have also obtained evidence that, in addition to c-Ki-ras, at least one other transcription unit has been amplified in the mouse adrenal tumor cells. Moreover, by Southern blot analysis of Chinese hamster-mouse somatic cell hybrids, we have determined that the amplified DNA sequences associated with DMs and HSRs, including the c-Ki-ras gene, are present in normal mouse cells on chromosome 6.