Further evidence for a heterochromatin-chiasma correlation in some Allium species

Abstract

Even in cases in which C-bands are intercalary in chromosomes of Allium carinatum and A. flavum, chiasmata are formed in immediately adjacent regions. This argues against considerations that there exists merely a spatial proximity between the commonly found distal chiasmata and the C-bands in corresponding regions, without any causal relation. Furthermore, a closely related species, A. sipyleum, without distinctly visible C-bands has a much less localized chiasma distribution in its bivalents.

Pleistocene karyotypic divergence in Hoplias malabaricus (Bloch, 1794) (Teleostei: Erythrinidae) populations in southeastern Brazil

“…On the other hand, John (1988) suggests that heterochromatin variation would be negative for some organisms, mainly due to the mechanisms that bring about these changes, such as multiple replication, unilateral amplification and deletion. John (1988) indicates that heterochromatic blocks inhibit chiasmata formation, even though this does not hold for Allium (Loidl, 1982). In the species complex Mus terricolor, Sharma et al (2003) observed variation in the heterochromatin in the short arms of autosomes, which would prevent synaptic association during meiosis.…”

The inter-relationship between heterochromatin distribution and chiasma distribution

“…Less commonly, where only single terminal Cbands are present, the chiasmata are situated in the euchromatin adjacent to the C-band (Loidl, 1979). Loidl (1982) is of the opinion that, in these cases, where there is a high correlation between C-bands and the occurrence of chiasmata in their vicinity, chiasma siting is of a direct consequence of C-band distribution. He bases this argument on two observations:…”

“…Loidl (1982) takes this to imply that the absence of distal C-bands determines the absence of distal chiasmata, although this does not explain the absence of proximal chiasmata.…”

Giemsa C-banding of Rhoeo (Commelinaceae)

“…Yunis and Yasmineh (1971) suggested that constitutive heterochromatin may serve several vital structural functions which include nuclear organization, protection of vital regions of the genome, aid in speciation or serve as an early pairing mechanism in meiosis. Constitutive heterochromatin in the telomeric region has also been suggested to facilitate chromosome pairing and synapsis (Fussell, 1973;Stack & Clarke, 1973;Ashley, 1979;Loidl, 1982). Natarajan and Natarajan (1972) previously proposed that centromeric heterochromatin in R. spathacea may act to strengthen the centromere~ organize chromosomes, prevent crossing over and act to initiate ring formation.…”