The Genus Collinsia. IV. The Cytogenetics of Colchicine-Induced Reciprocal Translocations in C. heterophylla

Abstract

1. At least one plant with a heterozygous reciprocal translocation was found in the progeny of each of sixteen of thirty plants of Collinsia heterophylla Buist (n = 7) treated by three different methods of application. 2. The interchange complex in the eighteen reciprocal translocations occurred either as a ring or chain of four chromosomes and as bivalents at metaphase I; the frequencies of each configuration were not constant for all the reciprocal translocations. 3. The orientation of ring and chain interchange complexes at metaphase I to give either an adjacent or an alternate orientation was not directed, since the two types of orientation occurred with approximately equal frequencies. 4. Although plants with a heterozygous reciprocal translocation usually had a lower percentage of stainable pollen grains, this criterion was not reliable for their positive identification. The mean number of seeds per capsule, however, was considerably lower for plants with, than for plants without, a heterozygous reciprocal translocation, and this number proved to be a reliable criterion for positive identification of the two types. 5. The progeny from plants heterozygous for a reciprocal translocation included approximately equal numbers of plants with and without a heterozygous reciprocal translocation. 6. The possibility that not all the chromosomes in the complement were involved in colchicine-induced reciprocal translocations is briefly discussed.