Frequency and distribution of chiasmata in Syrian hamster spermatocytes studied by the BrdU antibody technique

Abstract

The frequency and distribution of chiasmata and the nature of terminal "associations" was re-examined in Syrian hamster spermatocytes using the 5-bromo-2'-deoxyuridine (BrdU) antibody technique (BAT) for differential chromatid labelling. Differential chromatid substitution was achieved by BrdU incorporation at the penultimate pre-meiotic S-phase followed by one of three different staining protocols: (i) fluorescence plus Giemsa (FPG), (ii) acridine orange staining or (iii) BAT. For analysis of chiasmata frequency and localization in the diplotene/diakinesis stages the resolution of FPG and acridine orange staining was comparable to that of BAT. In metaphase II chromosomes BAT was more informative than FPG and acridine orange staining and revealed small, terminal crossover exchanges. This finding proves that many terminal associations of meiotic chromosomes actually represent chiasmata at the end of the first meiotic division. Some crossover exchanges were localized in the constitutive heterochromatin of autosomes. Using BAT we also detected crossover exchanges in close vicinity to each other. This observation is reminiscent of the fact that crossing over interference means a reduction in frequency and does not imply total inhibition.

Chromosome organization and chromatin modification: influence on genome function and evolution

“…Their selective use for recombination would avoid rearrangement-prone recombination by providing an opportunity for 'safe' crossovers that would maintain genome integrity without gain or loss of sequences. Consistent with this assumption, ␤ -hetero-chromatin in the Syrian hamster accounts for 30% of the total autosomal fraction of the genome (Taruscio and Manuelidis, 1991) and meiotic recombination does occur within the ␤ -heterochromatin of this species, despite its repetitive composition (Latos-Bielenska and Vogel, 1990) ( Fig. 1 ).…”

“…1 ) were initially distinguished in mammalian metaphase chromosomes by the different rates at which they lose basophilia during treatment with either trypsin (R-bands 1 G-bands) or the acid-base-warm salt treatments of the C-banding procedure Mammalian Autosomal Genome tin, the ␣ -heterochromatins of centric tandem repeats and the ␤ -heterochromatins present in some species, are always heterochromatic. Both are darkly staining by C-banding (Latos-Bielenska and Vogel, 1990). Supernumerary B-chromosomes, parasitic chromosomes that are not essential to the organism but exist in some species, may be ␤ -heterochromatin.…”

Cytomorphological Studies in some species of Chrysanthemum L. (Asteraceae)

“…In cytological method, recording of numbers and locations of chiasmata at late prophase I and metaphase I of meiosis demonstrate the physical exchange between homologous non-sister chromatids (Tease and Jones 1978;Latos-Bielenska and Vogel 1990). This represents an efficient approach, by rapidly scoring large number of meiocytes, to genome wide levels of recombination as well as the distribution of recombination events within chromosomes.…”

Effects of supernumerary heterochromatin on chiasma formation and chromosome segregation in Dociostaurus genei (Orthoptera)

“…One of these deems terminal associations to represent true chiasmata (Jones & Tease, 1984;Jones, 1987;Latos-Bielenska & Vogel, 1990;Santos & Esteban, 1990), whereas the other considers that they are achiasmate contacts (John & King, 1985;Wada & Imai, 1995;Benavente et al, 1996).…”