Radioactive In Situ Hybridization to Replication-Banded Chromosomes

The technique of radioactive in situ hybridization of chromosomes is increasingly being replaced by nonisotopic methods. Amongst the principal reasons for this are greater convenience, resolution, safety, and speed offered by the nonradioactive methods; and the computerization of digital imaging microscopy, which has allowed previously unachievable maneuvers such as complex multicolor chromosome painting. Such a swing in preference is attested by the disproportionate application and publication of new sophisticated protocols based on the nonisotopic methods in recent times. However, the “fossilizing” radioactive procedure still holds a significant place in various chromosomal studies because of some of its unique features. For example, it offers an acceptable way of quantitating signal (and thus DNA sequence) distribution on different chromosomal sites (1 –7 ) In laboratories where the more elaborate digital imaging equipment is not available, extended autoradiography offerred by radioactive in situ hybridization provides the sensitivity otherwise unattainable with nonradioactive approaches, especially when small probes or heterologous probes are used (see Chapter 15 ). Also, the hybridization slides and results obtained will form a permanent record that can be conveniently assessed or reassessed without any further treatment over a period of weeks, months, or even years.