MORPHOLOGY OF PACHYTENE CHROMOSOMES AND MEIOSIS IN MANIHOT-ESCULENTA CRANTZ

Detailed analyses of chromosomes at pachytene and later stages of meiosis were made in a cultivated type of cassava. Pachytene chromosomes are depicted on the basis of total length, relative length, arm ratio, amount and distribution of heterochromatin and number and position of chromomeres. Idiograms showing details of all the eighteen pachytene bivalents in the haploid complement are presented and based on the average values of lengths obtained by accurate measurements of the bivalents in a minimum of 15 completely analyzable nuclei, the eighteen pachytene bivalents have been arranged and numbered in order of their decreasing length as chromosome I to chromosome XVIII. The haploid chromosomal complement, inter alia, has three functional nucleolar chromosomes and six chromosomal types represented in duplicate. Based on the data of the pachytene karyology obtained, a segmental allopolyploid origin of the present day cultivars of cassava has been suggested. Based on cytological data, it has been suggested that meiotic abnormality is not the cause of pollen degeneration in the material studied. © 1969, Japan Mendel Society, International Society of Cytology. All rights reserved.