Double Y as an indicator in a test of mitotic nondisjunction in cultured human lymphocytes

A cytological test for the detection of non-disjunction in human cultured lymphocytes has been developed. The Y chromosome was used as a marker, because this chromosome is easily identifiable in mitosis after staining with quinacrine dihydrochloride without karyotyping. Non-disjunction can be directly revealed by scoring mitoses with two Ys. The test was applied to agents known for their ability to induce numerical and/or structural changes in chromosomes, namely benomyl, colcemid, distamycin A, mitomycin C and X-rays. In treated lymphocytes, increased frequencies of YY mitoses were found, ranging from 2.5 X 10(-4) to 61.2 X 10(-4) (control value less than or equal to 1.1 X 10(-4). The results suggest that the detection of fluorescent Y chromosomes on metaphases is suitable for determining induced non-disjunction in human cultured cells.