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

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 (32P and 35S) 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.