Heteromorphic a Chromosomes of the Tomato Differing in Satellite Size.

In cultivated tomato plants which were largely but not exclusively derived from triploids, chromosomes of two distinct sizes were found associated with the nucleolus in the pollen mother cells. Since a trivalent was found on the nucleolus in the simple trisomic type, triplo-A only, evidently it is the A or first chromosome which is dimorphic. At somatic metaphase this chromosome has a distinct satellite. Satellites of two sizes were found on the nucleolus in early prophase of somatic mitosis, and the difference in the length of the satellites corresponded to the difference in the length of the respective A chromosomes in the pollen mother cells. It is the length of the satellite which differs in long and short A chromosomes, the remainder of the chromosome appearing the same. Diploid plants have either a pair of long A chromosomes (“long long”), a pair of short (“short short”), or a long and a short A chromosome (“long short”). The remaining eleven pairs of chromosomes show no corresponding size difference or changed association in long A long A, short A short A, or long A short A plants.