It has been suggested that in species with monocentric chromosomes axial element (AE) components may be responsible for sister chromatid cohesion during meiosis. To test this hypothesis in species with holocentric chromosomes we selected three heteropteran species with different sex-determining mechanisms. We observed in surface-spreads and sections using transmission electron microscopy that the univalent sex chromosomes form neither AEs nor synaptonemal complexes (SCs) during pachytene. We also found that a polyclonal antibody recognizing SCP3/Cor1, a protein present at AEs and SC lateral elements of rodents, labels the autosomal SCs but not AEs or SC stretches corresponding to the sex chromosomes. Cytological analysis of the segregational behaviour of the sex univalents demonstrates that although these chromosomes segregate equationally during anaphase I they never show precocious separation of sister chromatids during late prophase I or metaphase I. These results suggest that AEs are not responsible for sister cohesion in sex chromosomes. The segregational behaviour of these chromosomes during both meiotic divisions also indicates that different achiasmate modes of chromosome association exist in heteropteran species.
Mean diplotene chiasma frequency is shown to be significantly and positively correlated with mean synaptonemal complex (SC) length in 21 males of Locusta migratoria belonging to three different families. This may reflect a direct causal connection between SC length and chiasma frequency or an indirect relationship arising from the action of other factors with effects on both parameters. Various interpretations of the correlation are discussed in the light of old and new information on synaptic and recombinational processes during meiotic prophase I.
Pachytene and zygotene stages have been analysed on silver stained spreads of synaptonemal complexes (SCs) from Chorthippus jacobsi spermatocytes. SC lengths are compared to those obtained from C‐banded mitotic metaphases. The pattern of meiotic pairing initiation and progression is described. In the submetacentric bivalents it is initiated from both chromosomal ends whereas in acrocentric bivalents two potential pairing initiation points are located in the long arms, the short arms remaining as late pairing regions. In addition, some interstitial pairing initiation points also occur, particularly in the L and M4–M5 bivalent groups. Shorter chromosomes commence and finish pairing relatively early. Interlockings form and are mostly resolved throughout zygotene. The estimated mean number of interlockings is 1.6 at zygotene as opposed to 0.17 at early–mid pachytene.
The meiotic behaviour of an iso‐B chromosome of the grasshopper Omocestus burri has been studied in a natural population located at Villar del Cobo (Teruel, Spain) by means of cytological observations of male and female meiosis. Whereas B chromosomes do not accumulate in the male germ line, they are included in the secondary oocyte at an increased frequency over mendelian expectations. Therefore, an accumulation mechanism of the accessory chromosome based on meiotic drive takes place in the females of this species.
Analysis of surface-spread synaptonemal complexes of zygotene and pachytene spermatocytes was carried out on centric-shift heterozygotes of grasshoppers. These rearrangements affected the M7 chromosome in Chorthippus vagans and the M6 and S8 chromosomes in Chorthippus apricarius. The shifts in the latter two chromosomes were also associated with C-heterochromatin variations between homologous chromosomes. Rearranged chromosomes proceeded directly to heterosynapsis without an apparent intervening homosynaptic phase in M7 bivalents of Ch. vagans and M6 bivalents of Ch. apricarius. In the latter case, axial equalization of the heterochromatin polymorphism was also achieved. On the other hand, asynapsis of the intercentromeric regions throughout pachytene was the rule in the centric shift involving the S8 chromosome of Ch. apricarius. In the three cases analysed, the production of unbalanced gametes in the heterozygotes is precluded either by the lack of chiasma formation in heterosynapsed rearranged segments or by the lack of pairing between such segments. Chiasmata were limited to the homologous regions of the heteromorphic bivalents.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.