Lines and varietes that are genetically identical.
In genetically modified plants, isogenic initial lines mean those non-genetically modified plants from which the GM strains are derived. Thus, the only difference between GM plants and their derivative isogenic line will be those genes that have been transferred transgenically.
Evaluating genetically modified plants for possible unexpected effects necessitates comparison with unmodified parental strains. In order to eliminate any possible influence of normal genetic variation between different hereditary lines and varieties, isogenic lines are usually used as a standard for comparison.