Complete deficiency of constitutive heterochromatin on a human chromosome 9.

In cultured amniotic fluid cells a mediocentric chromosome 9 appeared to be completely deficient in constitutive heterochromatin when stained with distamycin A and DAPI. In addition, this deficient chromosome was found in a blood cell culture from the father. Both the father and the child after birth were phenotypically normal. Evidently, a considerable heterozygotic deficit of chromosome 9 heterochromatin can be tolerated without affecting the phenotype. The heterochromatin defect was also shown by G11-staining. Distamycin A-DAPI staining is highly reproducible and is recommended as a fluorescent alternative to often less successful G11-methods for the detection of heteromorphism of chromosome 9.