We have studied female cousins with partial duplication of 12q. The cousins' mothers (who are sisters) and the maternal grandmother and great grandmother carried a balanced translocation between chromosomes 11 and 12. We have compared our patients with eight other reported cases of partial duplication of the same chromosome segment (12q24----12qter). Placement of the extra material seems to have little effect on the anomalies present; (only two other cases involved chromosome 11). We propose that our patients provide further evidence that duplication of 12q leads to a clinically identifiable syndrome.

A case of pure 12p trisomy was discovered in a 14‐year‐old boy during a cytogenetic survey of Egyptian students attending a school for mentally retarded children. The patient had a normal birth weight but later showed developmental delay. Clinical examination at 14 years of age revealed a high bulging forehead, broad and flat nasal bridge, large mouth with everted lower lip, folded upper ear helix with protuberant antihelix, pectus excavatum, undescended testes, flat feet, generalized hypotonia and moderate mental retardation. Chromosomes analyzed from blood lymphocytes showed an enlarged short arm with an additional band on one of the no. 12 chromosomes. The duplicated chromosomal material extended from 12pter→p12.2, including the LDH‐B locus, which showed a gene‐dosage effect. This extra chromosomal material arose de novo by tandem duplication. The parents' chromosomes were normal.

Bacteriophage T5 did not grow at the nonpermissive temperature of 42°C in Escherichia coli carryipg a temperature-sensitive mutation in gyrB [gyrB(Ts)], but it did grow in gyrA(Ts) mutants at 42°C. These findings indicate that the A subunit of host DNA gyrase is unnecessary, whereas the B subunit is necessary for growth of T5. The necessity for the B subunit was confirmed by a strong inhibition of T5 growth by novobiocin and coumermycin A1, which interfere specifically with the function of the B subunit of host DNA gyrase. However, T5 growth was also strongly inhibited by nalidixic acid, which interferes specifically with the function of the A subunit. This inhibition was due to the interaction of nalidixic acid with the A subunit and not just to its binding to DNA, because appropriate mutations in the gyrA gene of the host conferred nalidixic acid resistance to the host and resistance to T5 growth in such a host. The inhibition by nalidixic acid was also not due to a cell poison formed between nalidixic acid and the A subunit (K. N. Kreuzer and N. R. Cozzarelli, J. Bacteriol. 140:424-435, 1979) because nalidixic acid inhibited growth of T5 in a gyrA(Ts) mutant (KNK453) at 42°C. We suggest that T5 grows in KNK453 at 42°C because its gyrA(Ts) mutation is leaky for T5. Inhibition of T5 growth due to inactivation of host DNA gyrase was caused mainly by inhibition of T5 DNA replication. In addition, however, late T5 genes were barely expressed when host DNA gyrase was inactivated.

A female fetus with multiple congenital anomalies was found to have double autosomal mosaicism, 47,XX,+8/ 47,XX,+14 on chromosome analysis via amniocentesis. At delivery, the proband displayed dysmorphic features of hypertelorism, micrognathia, low set ears, cleft palate, clubfeet, omphalocele, absent gallbladder and congenital heart defects. Fluorescence in situ hybridization demonstrated a marked discrepancy in cell line populations in the tissues examined.

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