Two isochromosomes were found at the diploid level: one following formalin treatment (curly-leaf mutant) and the other following ammonia treatment (dark-green mutant). The two arms of the isochromosomes paired with each other or one of the arms paired with the homologous arm of the normal chromosome to varying lengths. Unpaired segments of both chromosomes either remained single or showed some non-homologous pairing in the chromatic zones. At diakeninesis the isochromosome appeared ring-shaped if a chiasma occured between the two arms, and in half the cells the chromosomes of the heteromorphic pair were present as univalents.
According to Barton's map of the pachytene chromosomes, the isochromosome of the curly-leaf mutant was composed of the two long arms of chromosome 9, and that of the dark-green mutant of the long arms of 8.
The curly-leaf mutant was characterized by its slow growth, curling of leaves, light-green color, thin stem, small fruits with dark-green radiating bands and pollen abortion. The dark-green mutant had dark-green leaves with few hairs and greater pollen sterility. The curly-leaf disomic mutant produced (i) normal plants, (ii) curly-leaf secondary trisomes and (iii) curly-leaf disomes, the last in an extremely small percentage.
The curly-leaf trisome had comparatively thicker leaves than the disomic mutant, semi-compound infloresence and smaller fruits. It produced (i) normal plants, (ii) secondary trisomes and (iii) primary trisiomes.
Another morphological mutant appeared following either treatment, characterized by its slow growth, thin stem, long internodes, elongated rachis, greyish-green color and pollen abortion. Lagging chromosomes were occasionally seen at meiotic anaphases. The elongate-leaf character was inherited at a low rate with production of trisomes. The elongate-leaf trisome had 2-3 loculed, oval, nipple-tipped fruit.
A study of inheritance of one of the morphologically and cytologically indistinguishable semi-sterile plants showed that pollen sterility factor was transmitted at a low rate. These plants may have either a small deficiency or a haplo-lethal mutant gene.