Rye chromosomes were selectively stained in the meiosis of triticale (Secale L.). In triticale a varying number of homologous chromosomes fail to pair at meiosis and are seen as univalents at first mietaphase (1, 2). It has been suggested (3-7) that these univalents are mainly chromosomes of the rye genome. This conclusion was based on two general observations made on octaploid triticale. First, some triticales have a strong tendency to revert to hexaploids that resemble wheat (3). Second, individual chromosomes of rye contributed to aneuploidy much more often than wheat chromosomes (5). By contrast, in hexaploid triticales a substantial number of the aneuploids were contributed by the wheat genomes as well (8, 9). However, in order to extrapolate from aneuploidy to meiosis, we must assume that all deficiencies will be transmitted with approximately the same frequency.Ideally what is heeded is a method whereby the genomic origin of the univalents themselves can be ascertained. Such a method was suggested to us by the recent reports (10-12) that in somatic cells of triticale the wheat and rye chromosomes can be strained differentially with Giemsa. Rye chromosomes generally carry at least one large and terminal band, unlike wheat chromosomes, where terminal bands are both infrequent and small. It is generally accepted that chromosome regions that strain differentially with Giemsa are heterochromatic.
MATERIALS AND METHODSGenotypes used were as follows: All pollen mother cell material was fixed in Carnoy's II. Mean