The Genus Collinsia. x. Aneuploidy in C. heterophylla

Abstract

1. Aneuploids of Collinsia heterophylla Buist (n = 7) with three (trisome) to seven (heptasome) replicate chromosomes could not be distinguished from each other or from diploids by any detectable alteration in gross morphology. 2. The extra chromosome in trisomes always occurred as a univalent at metaphase I; bivalents and univalents were observed in tetrasomes; multivalents were noted in pentasomes and polyploids. 3. The extra chromosome was transmitted by the pollen from trisomics with a frequency ranging from 25 to 65%; except in one line, pollen from tetrasomics usually had n + 1 chromosomes; pollen with n + 2 or n + 3 chromosomes was produced by aneuploids with more than two extra chromosomes. 4. Trisomics used as seed-parents yielded tetrasomics, the frequency being determined by the specific line; progenies from tetrasomic seed-parents included numerous tetrasomics. 5. Heptasomes (2n + 5) represented the upper limit of the number of replicate chromosomes in a plant. 6. Progenies from certain self-pollinated aneuploids did not include plants with the specific chromosome numbers to be expected on the basis of the chromosome numbers of plants in the progenies from these aneuploids used as pollen- or seed-parents. 7. Trisomics were as fertile as diploids; aneuploids with two or more extra chromosomes had a greatly reduced seed-set. 8. Probable mechanisms responsible for the absence of multivalents in trisomes and tetrasomes and for the occurrence of tetrasomics in progenies from trisomic and tetrasomic seed-parents are discussed.