Polyploidy, body size, and opportunities for genetic enhancement and fixation of heterozygosity in plants

Polyploidy, the presence of more than two chromosome sets, is rare in animals, but is wide spread in plants. Polyploidy is believed to play an important role in speciation and diversification of plants. It is conjectured that almost all angiosperms are likely to be ancient polyploids i.e. palaeopolyploids that have undergone diploidization through differential mutation, elimination and inversion of duplicated chromosomes. Therefore, understanding of consequences of gene duplication on functional divergence, developmental behavior and genome stability is of utmost importance from utilitarian view point. Studies conducted by our group for over a quarter century on the cyotogenetics of polyploids on an array of medicinal and aromatic plants have enabled us to develop strategies to realize high fertility in the autotetraploids. It is surmised that pre-selection of diploid progenitor with low chiasmate association, preferably with distal chiasma localization facilitates high bivalent pairing and balanced meiotic segregation in the derived autotetraploid, and thereby promising high fertility. This has implications in ploidy mediated fixation of heterozygosity and genetic enhancement. However, the elevated ploidy level does not always bring about increase in body size. Both, increase or decrease in body size happen to occur consequent to genomic duplication, depending upon the species and composition of native secondary metabolites / cost of metabolic load. Of course, polyploidization does bring about increase in secondary metabolite concentration and DNA methylation. Further, the patterns of chromosome / ploidy variation encountered in callus cultures over passage of subcultures are indicative of variation happening over evolutionary timescale. The details concerning such issues are dealt in this article based on our own experimental observations and are discussed from utilitarian view point for further researches.