Squash dot hybridization
The in-situ hybridization technique is often used for locating the position of the repeat sequence (including sat-DNA) on a specific chromosome. However, in some cases the repeated DNA from an alien species is used for detecting the presence of chromatin material introduced from this species in a crop plant due to introgression. Sometimes, a cytogeneticist may need to screen large population of a crop species to select plants that may carry alien genetic material. Squash dot hybridization technique is designed for this purpose. In this technique one root tip from a germinated seed may be squashed onto nitrocellulose filter and the filters are hybridized with radioactively labelled repeated DNA probe derived from the alien species in question. After washing the filters in appropriate buffers, they are used for exposure of X-ray film, which on developing gives the desired information about the presence of alien genetic material. The successful use of this technique has actually been demonstrated to detect the presence of introgressed rye chromatin in several wheat cultivars, through the use of highly repeated DNA probes derived from rye.