Application of DNA-DNA hybridization of dual labeled probes to the detection of trisomy 21, monosomy 21, and sex determination.

[monosomy 21]

Chromosomal aneuploidy is usually identified by cytogenetic methods . However , for some purposes it would be desirable to have an easier method of recognizing specific trisomies or monosomies . We have devised such an assay . It involves the simultaneous hybridization of two chromosome-specific DNA probes labeled with different isotopes (32 P and 35 S ) to human chromosomal DNA immobilized on a nitrocellulose filter . The hybridization signals are then counted , and the dpm ratios between the two isotopes are determined . In this paper we show the application of this technique in sex determination , in the analysis of two human cell lines reported to have chromosome 21 monosomy , and , especially , in testing for Down syndrome .