Introduction to Polyploidy

Abstract

Polyploidy refers to the presence of more than two genomes per somatic cell. Generally, the polyploid organism would have multiple sets of chromosomes or either the combination of chromosome sets found in same species or a closely related diploid species. Polyploid organisms can arise spontaneously by the chromosome duplication of somatic cells, or they can arise during meiosis due to non-disjunction of homolog chromosomes giving rise to diploid gametes (Ramsey and Schemske 2002). Polyploidy can also be induced artificially in the laboratory by drug treatment of the cells of an organism which inhibits the cell division, e.g. colchicine. In nature the polyploidy exists in organisms in either all or some somatic cells. The prevalent occurrence of polyploids suggests that polyploidy confers some selective advantages over diploidy. Some of the advantages can be enhanced vigour, increased heterozygosity, novel variation and production of new genotypes and allelic sub-functionalization (Salmon et al. 2005; Udall and Wendel 2006; Abbott et al. 2007; Anssour et al. 2009; Dar et al. 2013). The ancestral condition of any eukaryote is now suspected to have gone through polyploidization and re-polyploidization (Blanc et al. 2003; Bowers et al. 2003; Tuskan et al. 2006; Jaillon et al. 2007). The return of many genes back to single copy with disomic chromosomal inheritance and, in some cases, to smaller genome size and reduced chromosome numbers can occur through diploidization. Diploidization mechanisms include events such as chromosomal translocations, deletion of repetitive sequences and gene silencing (Pontes et al. 2004; Han et al. 2005; Gaeta et al. 2007; Mandáková et al. 2010).