Central Potato Research Institute, Simla-1
Online published on 25 January, 2012.
A method has been proposed for the estimation of generalized differences, d2 values, among the karyotypes which allow a critical evaluation of the karyotype asymmetry. This method has been used to evaluate the karyotype asymmetry of the different putative genome donor species and of different genomes of tetraploid ‘Cappeli’ wheat and hexaploid wheat variety ‘Chinese Spring’. The analyses bring out the following points of evolutionary significance.
(i) Among the different genomes of polyploid wheats analysed, the B genome shows the highest order of asymmetry followed by the A genome with the D genome showing the most symmetrical karyotype.
(ii) Out of the seven homeologous groups, group V is the most asymmetrical, groups VI and VII being most symmetrical. The d2 values were higher at the hexaploid than at the tetraploid level.
(iii) Comparison of the d2 values of the putative genome donor species and the genomes in polyploid wheats indicate that:
(a) genome A has the same order of karyotype asymmetry as the present forms of einkorn wheats;
(b) the B genome of polyploid wheats could have had a polyphyletic origin; and (c) the present day forms of Ae. squarrossa show much higher d2 values than the D genome of hexaploid wheat ‘Chinese Spring’.
