There is an upper limit of chromosome size for normal development of an organism

A clearly definable upper tolerance limit for chromosome arm length has been found. As a rule we postulate that, for normal development of an organism, the longest chromosome arm must not exceed half of the average length of the spindle axis at telophase. Above this length, fertility and viability of the carrier individuals become severely impaired due to increasingly incomplete separation of the longest chromatids during mitosis, resulting finally in the loss of DNA. The experimental work that points to a limit in genome plasticity has been carried out on a series of field bean lines with karyotypes of considerable variation in length of individual chromosomes.