Effects of constitutive heterochromatin and genotype on frequency and distribution of chiasmata in the seven individual rye bivalents.

Number and distribution of chiasmata were studied in the single pair of homologous rye chromosomes in 29 chromosomal F1 hybrids between the seven disomic wheat rye addition lines of 'Chinese Spring'/ 'Imperial' and five selected inbred genotypes of cultivated rye by using the differential Giemsa staining technique. The results indicate that the number and position of chiasmata is independent from the amount and position of C-heterochromatin. Genotype had an effect on chiasma number, whereas chiasma distribution within bivalents appeared to be determined by morphological features of chromosomes. Late replicating DNA in constitutive heterochromatin may delay the separation of half bivalents if chiasmata are formed between them and the centromere.