Three approaches

The technique is a form of differential display, according to Steve Lombardi, division vice president for genetic analysis at the PE Applied Biosystems division (Foster City, Calif.). He divided gene expression into three types of technologies: gene counting approaches, probe-based approaches, and imaging techniques including differential display.

The problem with counting approaches is that "if you want to quantify all the genes expressed in a tissue, you have to sequence a huge amount of redundancy that requires a lot of time and expense," he said, "and you statistically have a very hard time identifying those genes which are minimally expressed."