Meiosis in Diploid and Colchicine Induced Tetraploid Zebrina pendula Schnizl., A Structural Hybrid

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Abstract
Cytological analysis of diakinesis and MI in Z. pendula. Schnizl. (n = 12) showed that about 48% of the cells contained chains of 3 chromosomes, and rings and chains of 6 and 4 chromosomes. There were never more than 2 of these associations /cell, nor more than 6 chromosomes involved in such associations. The remainder of the chromosomes were formed into bivalents and univalents. Chains, and rings of 3,4 and 6 chromosomes are formed as a result of reciprocal translocations between non-homologous bivalents. Univalents are the result of a failure of chiasma formation or non-disjunction of multiple associations at AI. Bridges with or without fragments were found in a low percentage of cells. Pollen sterility is high. The colchicine induced tetraploid of Z. pendula (n = 24) formed mostly bivalents. The predominance of bivalents in the tetraploid is explained by assuming preferential pairing between identical partners of chromosomes furnished by the diploid. The divergent results of different investigators is believed to be due to geographical variation in this species which is undergoing relatively rapid chromosome evolution by spontaneous structural rearrangements in somatic chromosomes.

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