Importance of teaching concepts of population genetics in effective understanding of plant breeding

Procedures of Plant breeding are based on applications of principles of Genetics and these principles relevant to plant breeding must be exhaustively covered before teaching procedures of plant breeding. It is proposed to present the new graphical, pictorial presentations especially based on equilateral triangle, bar diagram etc., developed for effective communication of these concepts. Method of reproduction and system of mating will influence the constitution of population released as a variety and in turn the breeding methods followed to develop an improved population such as a homozygous genotype in self pollinated, a heterozygous homogenous population in asexually reproduced crop and an equilibrium population in cross pollinated crops. Consequences of random mating, attainment of equilibrium, constancy of allelic frequency during this process of attaining equilibrium and relationship between allelic and genotypic frequencies (square law) will help in getting a proper perception of the implications of Hardy-Weinberg equilibrium in breeding cross pollinated crops. Selection as a potent force in altering allelic frequencies can be explained by quoting practical situations and consequences when selection is practiced for a quantitative trait which is influenced by loci showing additive gene action, dominance and even over dominance gene action. This helps the student to link response to selection (improvement in yield) with change in allelic frequency and about how response is difficult at loci showing high degree of dominance in both self and cross pollinated crops. Consequences of allelic frequency differences in sexes leading to a disequilibrium population can be important base to understand explain maximizing heterosis. It gives an idea about the relationship between allelic frequency difference (y) and frequency of heterozygous in Ft (performance of hybrid) and further explains why varietal hybrids are less potential than inbred based hybrids. It convinces about need for maximizing allelic frequency differences between parents (genetic distance) as the principle involved in population improvement schemes supporting hybrid breeding. Consequences of inbreeding, in terms replacement of allozygous genotypes by autozygous genotypes, increase in homozygosity (linking it with inbreeding coefficient) forms the base for explaining consequences of selfing after hybridization. It gives correct understanding of the changing constitution of F2 and succeeding generations. A comparison of F2 and F6 populations helps in distinguishing pedigree, bulk and single seed descent methods of breeding. Some new forms of presentations are developed to depict similarities and differences in consequences, the proportions of alleles of parents in self, limited and full back cross breeding (considering both self and cross pollinated crops) and a correct perception of target genotype based choice of breeding methods. Inheritance pattern of quantitative character, the break up of Genotypic value (A+D+l), linking these with these with combining ability effects become important. The corresponding components of genotypic variance are very helpful in understanding and linking heritable variability and response to selection. Simplified representations of inbreeding depression and heterosis, the factors influencing exploitation of heterosis must be understood to get a better insight in to principles of heterosis breeding, developing synthetics etc.