Detection of species specific chromosomes in somatic cell hybrids

We describe an in situ hybridization technique which allows rapid identification of species-specific chromosomes in somatic cell hybrid lines. Chromosome preparations from rodent-human hybrid lines are hybridized to biotinylated total human DNA which is subsequently detected by a series of immunocytochemical reactions which culminate in a peroxidase reaction visible by light microscopy. This technique not only allows identification of intact human chromosomes but also fragmented and rearranged human chromosomal segments. We have detected as little as 1 X 10(7) bp of human DNA inserted into a mouse chromosome using this procedure and estimate that the sensitivity of the technique would allow detection of sequences 5- to 10-fold smaller. The usefulness of the technique for screening hybrid cell gene mapping panels is discussed.