-Constitutive heterochromatin was observed in Lathyrus aphaca, L. cicera, L. odoratus, L. sativus and L. tingitanus. C-bands in L. odoratus and L. tingitanus are centromeric or proximal in location. In L. tingitanus, only the short arm of Chromosome 3 showed a large telomeric band; this was detected by C-banding following Q-banding but not in directly C-banded preparations. In L. odoratus, while most C-bands showed as positive Q-bands with enhanced fluorescence, small telomeric bands showed no differentiation with quinacrine. In L. tingitanus, constitutive heterochromatin showed two types of Q-band: one negative with quenched fluorescence at the centromeric regions of all the chromosomes and the other, positive with enhanced fluorescence at one or both sides of the negative bands. No other species of Lathyrus investigated showed discrete negative Q-bands. In L. aphaca and L. cicera. Q-banding patterns are characterized by large telomeric positively fluorescent bands on most members of each complement. Some chromosomes have proximal and/or intercalary bands. In L. cicera, some C-bands showed no differentiation with quinacrine staining. In L. aphaca, a large positive Q-band normally at the end of the short arm of Chromosome 6 is sometimes replaced by two small intercalary bands. Prominent telomeric positive Q-bands were also detected in L. sativus together with small proximal bands and intercalary bands. Whole short arms of Chromosomes 3 and 4 and the long arm of Chromosome 6 in L. sativus showed slightly quenched quinacrine fluorescence. The evolutionary implications of these observations are discussed.

Mixed first and second division restitution in male meiosis of Hierochloe odorata (L.

No abstract

SUMMARYMeiotic pairing is described for a completely homozygous tetraploid derived from successively doubled haploid barley. The high quadrivalent frequency (4.58/cell) in cells with many chiasmata is indicative, either of discrete pairing at only two independent synaptic sites per chromosome or of continuous pairing amongst many sites in close proximity. A high frequency of discordance amongst ring quadrivalents (20.8 per cent) leads to lagging and irregular segregation in at least 20 per cent of first meiotic divisions.

C0 autotetraploids have been derived from seven diploid (x = 7) species of Lathyrus, varying in genome size (11-20 pg DNA/2C) and content of moderately repetitive DNA (5-12 pg/2C). Pairing patterns at metaphase-I in 942 pollen mother cells (PMCs), each with a minimum of 28 chiasmata, were compared with a model relating pairing autonomy to genomic organization. Autotetraploids of one species, L. aphaca, form on average one multivalent more than those of the other six (5.2 vs. 3.7-4.2/PMC). With the exception of L. aphaca, intergenomic differences in bivalent frequency and incidence of synaptic exchange correlate with the size of the genome, particularly that of the moderately repetitive component. Such nucleotypic correlations appear to reflect losses in numbers of autonomous synaptic sites, concomitant with concerted reductions in the size of the genome. They also indicate that autonomous synapsis may be governed by moderately repetitive sequences.