Characterization of Somoclonal Variation - Somaclonal variants isolated through cell selection are often unstable; the frequency of stable variants may range from 8-62%, perhaps depending on the species and the selection agent. Many selected clones fail to exhibit their resistance during further screening or selection; obviously these clones are susceptible and were misclassified as resistant (they are called escapes).

Several clones lose their resistance to the selection agent after a period of growth in the absence of selection pressure. Such clones are called unstable variants and may result from changes in gene expression and from gene amplification (increase in the number of copies of a gene per genome of the organism in comparison to that naturally present).