A Possible Effect of Heterochromatin on Chromosome Pairing

Abstract

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

Meiotic expression of modified chromosome constitution and structure in × Triticosecale Wittmack

“…In hexaploid triticale (Thomas and Kaltsikes, 1974;Lelley, 1975b;Schiegel, 1978a;Jung and Lelley, 1985a, b;Jung et aL, 1985;Galindo and Jouve, 1989) and in wheat-rye addition lines (Schlegel, 1978b;Orellana et a!., 1984), rye Fominaya and Orellana (1988) demonstrated a phenomenon of interference between wheat and rye chromosomes as a cause of the decrease of rye-rye and wheat-wheat homologous pairing observed at metaphase I in triticale with respect to their corresponding rye and wheat parents.…”

Analysis of self-fertilization and meiotic behavior of eleven Brazilian triticale cultivars at two sowing dates

“…Thomas and Kaltsikes (1974) attributed the reduced pairing of the rye chromosomes, relative to wheat chromosomes in triticale, to the greater amount of heterochromatin in the rye chromosomes. On the other hand, Fominaya and Orellana (1988) found no relationship between the amount of heterochromatin in the rye chromosomes and reduction of pairing of chromosomes in octaploid triticales.…”

Interactions between wheat, rye and Aegilops ventricosa chromosomes on homologous and homoeologous pairing

“…At least in the first backcross hybrids ABRR and DUnRR the dosage of wheat and ventricosa genomes have been reduced with respect to the parental amphiploids (AABBRR, DDUnUnRR), and however the rye-rye homologous pairing is lower than in those amphiploids (table 1) (see Naranjo and Lacadena, 1982;Cermeño et al, 1985). Thomas and Kaltsikes (1974;1976) and Roupakias and Kaitsikes (1977) concluded that the presence of telomeric C-heterochromatin on rye chromosomes could be responsible for the rye meiotic irregularities observed in triticale and wheat-rye combinations, since heterochromatin is late replicating and therefore DNA replication of C-heterochromatin could interfere with meiotic prophase pairing. Nevertheless, this cannot explain our results because if the only cause of the decrease of the rye homologous pairing was the presence of telomeric C-blocks in the rye chromosomes, we would expect the same behaviour in the amphiploids as in the hybrids, and in the Ae.…”