Replication of chromosomal DNA in cultured abnormal human cells.

The replication of chromosomal DNA in a series of abnormal human cell cultures has been studied by means of DNA-fiber autoradiography. In lymphocytes with trisomy 21, in fibroblasts of 45,X;47,XXX;49,XXXXY; and 49,XXXXX chromosomal constitution, and in fibroblasts from a patient with xeroderma pigmentosum (De Sanctis-Cacchione syndrome), the rate of DNA replication does not differ from that in normal cells, varying in a single fork from 0.2 to 1.0 micrometer/min with a mean of about 0.6 micrometer/min. In fibroblasts with trisomy 7 the rate of DNA replication is greater, varying from 0.3 to 1.2 micrometer/min with a mean of about 0.8 micrometer/min. The sizes of replication units in all cells examined are from 80 to 500 micrometer with a mean of about 200-300 micrometer.