Specialization in the behaviour of chromosomes on the meiotic spindle

The kinetic activity of chromosomes is either distributed evenly along the length of the chromosome or localized in a single centromere. Within the group of organisms with evenly distributed (holokinetic) activity great variation occurs, which has its consequences for chromatid segregation. Three major types, with some overlap, can be distinguished. They form a gradient of increasing specialization. Arguments are presented for the hypothesis that the monokinetic chromosomes are nothing but the end point in the same gradient and do not form a fundamentally different category. These arguments include: concentration of kinetic activity at meiosis in some types of holokinetic chromosomes, and atavistic traits in monokinetic chromosomes pointing to a holokinetic origin. Possible reasons for the wide distribution of monokinetic chromosomes in the more evolved taxa are given.