| From these data it is clear that T. aestivum has seven chromosomes
which pair very closely with those of Ae. squarrosa. Thus final confirmation
is provided of the equivalence of the chromosomes of Ae. squarrosa
and those of the D genome of wheat. Naturally these new data lead to further comparisons and problems, two of which will be briefy mentioned. First the pairing between the D genomes of T. aestivum and Ae. squarrosa is much closer than that between the A genomes of T. aestivum and T. monococcum. This presumably reflects the more recent separation of the D genomes, which have consequently diverged less in structure and gene content than the A genomes. Secondly, it is notable that no more than seven bivalents, and no multivalents were observed. Thus there is no more pairing than can be accounted for by associations within the D genome. This suggests that pairing in euhaploids of T. aestivum can rarely occur between A and B genome chromosomes. Indeed examination of the results of Sears and Okamoto, on the chromosomes which pair in euhaploids, shows that the majority of pairing is either between A and D genome chromosomes or within the A genome. Thus diploidisation appears to be more effective for the A and B genomes than for these two genomes and the D genome. |
| <-- Back |