BioGenetics Lab, Inc

DNA & Protein Genotype Profiling Service

Isozyme Purity Testing

About Isozyme Purity Testing.

Isozyme marker loci have been available for use in quality assurance, variety identification, plant breeding, production and variety protection programs for more than four decades. Isozyme marker loci continue to be used for inbred purity, hybrid purity, inbred homozygosity determinations, inbred cleanup and hybrid cleanup. Isozyme loci are usually the markers of choice for identifying and quantifying offtypes in inbred lines and selfs and offtypes in single-cross hybrid populations populations of maize, sunflowers, tomatoes, melons, etc.

Isozyme marker loci have many advantages for use in determining purity of corn or sunflower populations. First, they are not affected by the field or greenhouse environment. They are cost effective compared to other methods and the turnaround time is relatively rapid. Since at least fifteen isozyme loci can be assayed simultaneously in a single individual of maize using a single buffer system, it is possible to identify outcrosses in inbred lines and selfs and outcrosses in single-cross and multi-cross hybrid populations with a very high level of precision and at a relatively low cost. In addition, multilocus analyses provide useful information for verifying inbred and hybrid genotypes.

There are two parameters that can be varied in the laboratory when conducting purity assays. The first is the number of individuals assayed per seed lot. The second is the number of isozyme loci assayed per individual.

We have conducted many statistical analyses over time to determine the appropriate number of individuals and isozyme marker loci to assay for inbred line and/or single-cross hybrid samples. The analyses routinely show that 100 random individuals are adequate in an inbred or single-cross hybrid population, as long as the number of polymorphic loci assayed is 10 or greater. Thus, BGL routinely assays a set of 11 to 15 polymorphic isozyme loci which can be assayed with a single gel buffer system.

We also have found that little is gained by assaying more than 100 random individuals with more than 11 polymorphic isozyme loci. Adding a 12th locus does not significantly improve the probability of correct classification of outcrosses (offtypes) in inbred lines or single-cross hybrids or selfs in a single-cross hybrid sample, as long as 100 or more individuals are assayed.