Genomes are usually regarded as static, changing only on the leisurely time-scale of evolution. This assumption clearly overlooks the changes in ploidy that cells in an organism undergo during various stages of growth and development. A mitotic cell doubles its ploidy during DNA synthesis and restores it subsequently at cell division. Polyploid cell types such as megakaryocytes (16n to 64n) or hepatocytes (2n to 8n) are commonly found during normal differentiation. Tumour cells have aberrant cell-cycle controls leading to an altered ploidy status. Further, deviation from the common theme of a haploid/diploid genomic constitution is widespread in the plant kingdom.