The chromosome field

摘要

Chromomere size gradients are the key phenomenon which opened the way to the concept of the chromosome field. With their regular pattern covering the whole chromosome arm and every arm of a complement, they led to the concept of a mechanism which accounts for the functioning of the chromosome as a whole. This chromomere gradient was observed in 73 species of plants belonging to 14 Families. The gradient is characterized by four main features: (1) In all cases studied large chromomeres appear on both sides of the kinetochore. (2) Once the phenomenon occurs in a certain species it occurs in all or most chromosomes of the normal complement. (3) The decrease in chromomere size proceeds from the kinetochore to the telomeres. (4) The gradient is maintained irrespective of the variation in length of the same chromosome from tissue to tissue. The occurrence of chromomeres of different sizes along the length of the chromosome is a phenomenon which depends not only on the effect of the kinetochore but also on the action of the telomeres. It is postulated that the interplay of two molecular messages originating at the kinetochore and at the telomere establishes a gradient of molecular concentrations along the length of the chromosome arm which ruthlessly forces given types of genes to become located at certain regions and not indiscriminately along the chromosome.