Spreading Synaptonemal Complexes from the Grasshopper Chorthippus Jacobsi: Pachytene and Zygotene Observations

Abstract

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.

Incomplete Synapsis and Chiasma Localization: The Chicken or the Egg?

“…2 J). It is interesting to point out that the sequence of appearance, development and pairing of the SMC3 axes is in close agreement with that displayed by AE/LEs and SC under electron microscopy [Santos et al, 1993]. As previously mentioned, ␥ -H2AX is restricted to unpaired portions of SMC3 axes during zygotene ( fig.…”

The Structure of the Synaptonemal Complexes in Meiocytes of European Domestic Goose (Anser anser)

“…The occurrence of interstitially located telomeric sequences on macrochromosomes is connected with an increase in the number of sites where formation of SCs is initiated, which explains why synapsis is achieved more rapidly. SANTOS et al (1993) observed that in submetacentric bivalents SC formation begins from subtelomeric regions of chromosomes. Two potential sites of initiation exist in acrocentric bivalents, i.e.…”

“…In geese the largest macrochromosomes are submetacentric, whereas microchromosomes are acrocentric, so the theory of SANTOS et al (1993) and the presence of interstitial telomeric sequences in chromosomes may provide an explanation to why macrochromosomes and not microchromosomes undergo synapsis first. Moreover, compared with macrochromosomes, microchromosomes are characterised by a lower adeninethymine content, accompanied by a higher guanine-cytosine content (FILLON et al 1998;GREGORY 2002).…”

Avian Meiotic Chromosomes as Model Objects in Cytogenetics

“…The occurrence of interstitially located telomeric sequences on macrochromosomes is connected with an increase in the number of places where the formation of SCs is initiated, which explains why synapsis is achieved quicker. Santos et al (1993) observed that in submetacentric bivalents synaptonemal complex formation begins from subtelomeric regions of chromosomes. In acrocentric bivalents there exist two potential initiation sites which are in the distal and proximal parts of the q arm.…”

“…9. Chromatin organisation in one-day-old gosling cells; isolation - Counce & Meyer (1973), staining -Howell & Black (1980 In geese the largest macrochromosomes are submetacentric whereas the largest microchromosomes are acrocentric, so the theory of Santos et al (1993) and the presence of interstitial telomeric sequences in chromosomes may explain why it is macrochromosomes and not microchromosomes that are the first to undergo synapsis. Moreover, compared with macrochromosomes, microchromosomes are characterised by a lower adenine-thymine content which is accompanied by a higher guanine-cytosine content (Fillon et al, 1998;Gregory, 2002).…”