In situ hybridization of a telomeric (TTA-GGG)n sequence to metaphases from three cases of ring chromosome, involving respectively chromosomes 4, 16, and 20, showed the presence of the cognate sequences in all three rings. To investigate whether these ring chromosomes originated by telomere-telomere fusion, we determined, by in situ hybridization, whether telomere-associated sequences and/or specific distal sequences were still present in the ring chromosomes. The finding that these sequences were preserved in all the ring chromosomes strongly indicates that they originated by telomere-telomere fusion. All three subjects carrying the ring chromosomes are affected by the so-called ring syndrome, with failure to thrive, minor dysmorphic signs and no major anomalies. The r(4) patient has the ring in mosaic form with a normal cell line and has normal intelligence. The r(16) and the r(20) patients have moderate mental retardation and suffer from seizures. We conclude that the ring syndrome, even in its more severe manifestation, is caused by ring chromosome instability.

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-Nine Sarda x Lacaune ewes with intersexual characteristics and an infertility condition at the reproductive anamnesis were analysed. In order to make a diagnosis, we have evaluated their behaviour and performed clinical and laparoscopic examination of the reproductive tract, as well as cytogenetic analysis. The ewes showed basically a female phenotype but a clinical examination revealed a different degree of masculinization in the morphology of external genital organs. A shorter vagina was observed in female-like ewes and a hypertrophic clitoris in male-like ewes. Laparoscopic analysis evidenced the presence of testis in seven individuals and, for two of them, the gonadal position was subcutaneous. Different male characteristics in the nine subjects, were also observed in their behaviour with a different degree of masculinization. Their blood samples were used for determining the percentage of male cells on lymphocytes chromosome spreads by using the C-banding technique. The haematopoietic chimeras (XX/ XY) found in the lymphocytes confirmed the diagnosis of freemartinism for seven out of the nine subjects.