In the cross between Zea mays (2n=20) and Tripsacum dactyloides (2n=72), observations in diakinesis have determined that the 36 Tripsacum chromosomes pair forming 18 bivalents, while those of maize form 0 to 5 pairs. In hybrids, the greatest frequency possess 23 pairs of chromosomes (see Figure 1).
Ten (10) pairs of chromosomes are formed during meiosis when maize conducts itself as a diploid. While in haploid cells there are only associations from 0 to 5, such associations are brought about between non-homologous parts of chromosomes (so-called freak "folding back," considered as pairing between the arms of the same chromosomes by Chase, Bot. Rev. 35:117, 1969). In pachytene observations, pairing of segments has not been found between maize chromosomes and those of Tripsacum. The forming of bivalents among maize chromosomes on one side and Tripsacum on the other agrees with the results obtained by other authors (Harlan et al., Science 167:1247, 1970), who manifest that such pairing frequency is influenced as much by the maize stock as by that of the Tripsacum used.
Ida Graciela Palacios and Jorge Luis Magoja
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