[en] Male pupae of the domesticated silkmoth, P. ricini were irradiated with 600 - 6000 R of ⁶⁰Co gamma ray and studied for the nature and frequency of visible chiasmata in the meiotic spermatocytes. Significant increase in lower doses (600, 1200 R) and decrease in higher dose (6000 R) were observed. More interstitial chiasmata were induced in the medium bivalents; and low frequency of terminals restricted to the smaller bivalents. The minimum chiasma per bivalent was one and never zero. Nature of monocentric versus holocentric chromosomes with regard to the gamma induced chiasmata were, however, discussed. (author)