Translocation heterozygosity in Coix
--P. Gayen, J. K. S. Sachan, Rajesh Kumar and K. R. Sarkar

Adaptive polymorphism for translocations exists sporadically in the genus Coix, an Asiatic relative of maize. There are a number of forms and species of Coix with chromosome counts of 10, 20 and 40. In naturally occurring populations of Coix from Western Ghat (Coix-21) and from Madhya Pradesh (Coix-63), rings of various sizes have been observed. In Coix-21 a ring quadrivalent was obtained in 60 percent of cells at diakinesis (Fig. 1) and one hexavalent was noted in about 12.5 percent of cells. The rest of the cells had 5 bivalents. The presence of quadrivalents (ring) or hexavalents (ring) is due to spontaneously occurring reciprocal translocations. In anaphase I, separation was observed, but a few cells with 1-2 lagging chromosomes, which might be a case of late separation, was noted. More than 80 percent of the cells had 5:5 separation in anaphase I and pollen fertility was 98 percent accompanied by high (about 80%) seed fertility. On the basis of these observations it might be assumed that this translocation heterozygosity is analogous to that which exists in Rhoeo and Tradescantia. In another population, Coix-63, 75 percent of cells had one quadrivalent, 7.5 percent of cells had one hexavalent (Fig. 2) and the rest of the cells had 5 bivalents at diakinesis. In anaphase I the majority of the cells (80%) had 5/5 separation, with unequal separation (6/4) in 20 percent of the cells. No cells with lagging chromosomes were noted. Pollen fertility was 75 percent and seed fertility was not as normal as in Coix-21. In this collection probably alternate segregation is higher, but the same amount of adjacent type is also there.

Figure 1. Ring quadrivalent at diakinesis in Coix-21.
Figure 2. Hexavalent at diakinesis in Coix-63.


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