IDENTIFICATION OF UNPAIRED CHROMOSOMES IN F1 HYBRIDS INVOLVING TRITICUM AESTIVUM AND T. TIMOPHEEV II

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Abstract
Nineteen lines of Trlti-cum aestivum ''Chinese Spring'' each carrying a different known telo-centric chromosome of the A or B genome were crossed with the amphi-ploid/T. timopheevii-T. tauschii (A. squarrosa). Each telocentric showed some pairing, presumable with a chromosome of T. timopheevii, but 6 of the 8 tested from the A genome paired in frequencies greater than 70%, while only 1 of the 11 of the B genome paired as much as 70%. This indicates that most of the pairing failure in T . aestivum-timopheevii hybrids involves chromosomes of the T. aestivum B genome and the corresponding genome of T. timopheevii. This and the variation between chromosomes suggest that structural differences, rather than genes causing asynapsis when heterozygous, are responsible for the lack of pairing. No such genes could be found on any of the 26 arms of timopheevii tested by being made hemizygous in the various hybrids. Ten of the 19 telocentrics studied were involved occasionally in multivalents, indicating the existence of at least 5 translocations between the parental species. The 2nd genome of T. timopheevii is considered sufficiently closely related to the B genome of T. turgidum and T. aestivum to be designated Bt. The differences from B are attributed to introgession of alien chromosomal segments following interspecific hybridization.