Electrophoresis Techniques

Genetic purity of a seed lot is important to know in the quality seed production. Genetic purity looks for differences in proteins (total protein profile or variety of enzymes) to create a "picture" for the variety or hybrid. Hybrid purity or variety characterization may assist a seed producer in developing and marketing their seed. Corn genetic purity is normally conducted with isozyme testing, while a variety of other crops can be tested for genetic purity with isoelectric focusing.

Isozyme Testing
Genetic purity testing is a quality assurance test to evaluate true-types, off-types, variants and self levels. Corn has ten pairs of chromosomes and genes at different locations on separate chromosomes that can code for different forms of each enzyme. The ten chromosome pairs have been mapped with known locations for various enzymes. Isozyme testing uses starch gel electrophoresis to separate the different enzymes by size, shape and charge. Reading the patterns at several locations gives a fingerprint of the corn being tested.

Hybrid and Inbred: Typically 100 individuals are tested. Male and female lines are run to determine the hybrid pattern. For hybrids, female selfs, variants, off-types and total purity percentages are determined. For inbreds, variants, off-types and total purity percentages are determined.

Verification: 10 individuals are tested.  These individuals are compared to the expected pattern.  The expected pattern is determined by testing a sample of the inbred seeds used to create the cross.  

Isoelectric Focusing
Isoelectric Focusing (IEF) can be described as electrophoresis in a pH gradient. It is a separation method that resolves proteins on the basis of their isoelectric points. The different molecular components of the protein are detected according to their position in the gel. This can be used on a variety of crops, such as rice, wheat, alfalfa and oats.

Inbred variety and hybrid purity testing is a quality assurance test to evaluate true-types, off-types and self levels. Typically 100 individuals are tested. Male and female lines are run to determine the hybrid pattern. For hybrids, female selfs, male selfs, off-types and total purity percentages are determined. For inbred varieties, off-types and total purity percentages are determined.