Chromosome elimination in a complex hybrid of the genus Hordeum

Abstract

Hybrid embryos, derived from the cross combining a Hordeum jubatum (4x) – H. compressum (2x) amphiploid and H. vulgare (4x), were observed and found to exhibit instability of chromosome numbers that resulted in an overall loss during the first 8 days of development in embryonic tissues. This instability seemed to be manifest as a progressive increase in the variability of chromosome numbers over this developmental period. The change in the overall mean chromosome number followed no discernible pattern with the exception that counts appeared to be clustered at numbers which are exact multiples of the basic chromosome number (x = 7). For each day postpollination, however, the mean chromosome numbers were significantly lower than the expected zygotic number (with one exception), indicative of net chromosome loss. Based on the data presented and cytological evidence, possible mechanisms are proposed to account for chromosome elimination in hybrid tissues. Chromosome loss may result from an incompatible interaction of the chromosomes and spindle-timing determinants originating from each genome during development or as a consequence of the malfunctioning of a proposed cytoplasmic organelle.