Chromosome number is key to longevity of polyploid lineages

Summary Polyploidy is ubiquitous and often recursive in plant lineages, most frequently resulting extinction but occasionally associated with great evolutionary success. However, instead of chromosome numbers exponentially increasing due to recurrent polyploidy, angiosperm species have fewer than 14 pairs. Following genome duplication, diploidisation can render one copy essential genes nonfunctional without fitness cost. In isolated subpopulations, alternate (homoeologous) gene copies be lost, creating incompatibilities that reduce hybrids between constraining exchange favourable genetic changes reducing fitness. When multiple sets incompatible are genetically linked, their deleterious effects not independent. The effective number independently acting loci limited by recombination. Therefore, many chromosomes subject a higher penalty during diploidisation. Karyotypic changes, especially fusions, flow normally disadvantages, the process, increase mixing differentially diploidised alleles. Fitness penalties caused favour accelerated karyotypic change, each change barriers flow, contributing speciation. Lower increased fusions confer advantages surviving process following polyploid formation, independent mechanisms.