Biochemical markers in genetic investigations of cultivated crops: the pros and cons

This literature review summarizes the accumulated knowledge and the author's own research data about suitability of seed storage proteins, allozymes and isozymes as biochemical genetic markers. These markers have a huge potential, since it allows researchers to distinguish genotypes from other in a short time. Therewith, biochemical markers are usually tissue- and organ-specific. The advantages that these markers possess over morphological markers are shown. So biochemical markers can be used on a much larger number of experimental objects than morphological ones. Protein markers are usually characterized by a greater correspondence between genotype and phenotype, and, besides, the path to the implementation of genetic differences into phenotypic ones for protein markers is much shorter than for morphological ones. In addition, metabolites (sugars, carbohydrates, secondary metabolites, etc.), which are identified biochemically after isolation from the organs or tissues of the studied organism and purification, are also referred to biochemical genetic markers. Though more than half a century has passed since the first description of biochemical markers, the physicochemical bases to their detection and identification have hardly changed methodologically. This gives some limitations on their use in genetic investigations. For example, it is shown, that plant protein polymorphisms revealed by one-dimensional electrophoresis can be subjected to quality and quantity changes because of ecological stresses such as nutrition deficiency or temperature deviations. Researchers also must take into account casual destructive changes and breaks of the analyzed molecules for various reasons, including due to non-standard conditions for protein and polypeptide extraction and purification, as well as during electrophoretic separation, which leads to non-specific electrophoretic spectra. Because of degeneracy of the genetic code and the fact that not every amino acid substitution leads to a change in charge and the molecular weight of the protein, only 30 % of nucleotide substitutions can cause electrophoretically detected protein polymorphism. Only strict observance of all methodological, biological and other restrictions, as well as established requirements, allow the correct and skillful use of biochemical markers in genetic research.