Sorting of chromosomes by magnetic separation

Chromosomes were isolated from Chinese hamster x human hybrid cell
lines containing four and nine human chromosomes. Human genomic DNA
was biotinylated by nick translation and used to label the human
chromosomes by in situ hybridization in suspension. Streptavidin
was covalently coupled to the surface of magnetic beads and these
were incubated with the hybridized chromosomes. The human
chromosomes were bound to the magnetic beads through the strong
biotin-streptavidin complex and then rapidly separated from
nonlabeled Chinese hamster chromosomes by a simple permanent
magnet. The hybridization was visualized by additional binding of
avidin-FITC (fluorescein) to the unoccupied biotinylated human DNA
bound to the human chromosomes. After magnetic separation, up to
98% of the individual chromosomes attached to magnetic beads were
classified as human chromosomes by fluorescence microscopy.