Asynaptic Regions Research Articles

Kinetic Activity of Chromosomes and Expression of Recombination Genes in Achiasmatic Meiosis of Tityus (Archaeotityus) Scorpions.

Several species of Tityus (Scorpiones, Buthidae) present multi-chromosomal meiotic associations and failures in the synaptic process, originated from reciprocal translocations. Holocentric chromosomes and achiasmatic meiosis in males are present in all members of this genus. In the present study, we investigated synapse dynamics, transcriptional silencing by γH2AX, and meiotic microtubule association in bivalents and a quadrivalent of the scorpion Tityus maranhensis. Additionally, we performed RT-PCR to verify the expression of mismatch repair enzymes involved in crossing-over formation in Tityus silvestris gonads. The quadrivalent association in T. maranhensis showed delay in the synaptic process and long asynaptic regions during pachytene. In this species, γH2AX was recorded only at the chromosome ends during early stages of prophase I; in metaphase I, bivalents and quadrivalents of T. maranhensis exhibited binding to microtubules along their entire length, while in metaphase II/anaphase II transition, spindle fibers interacted only with telomeric regions. Regarding T. silvestris, genes involved in the recombination process were transcribed in ovaries, testes and embryos, without significant difference between these tissues. The expression of these genes during T. silvestris achiasmatic meiosis is discussed in the present study. The absence of meiotic inactivation by γH2AX and holo/telokinetic behavior of the chromosomes are important factors for the maintenance of the quadrivalent in T. maranhensis and the normal continuation of the meiotic cycle in this species.

Complex Chromosomal Rearrangement Causes Male Azoospermia: A Case Report and Literature Review

Background: Male carriers of complex chromosomal rearrangements (CCRs) may have decreased fertility and usually present with azoospermia, oligospermia or teratospermia. Methods: High-resolution karyotype analysis using G-banding on peripheral blood lymphocytes was performed in an azoospermic male. Copy number variations (CNVs) were detected by chromosomal microarray analysis, and genetic variations were determined by long-read nanopore sequencing with Sanger sequencing for breakpoint confirmation. Results: The karyotype of the patient was 46,XY,t(4;21)(p11;p11),t(5;6;14)(p13q22;p22q22;q22), which did not involve CNVs with clinical significance. Twelve breakpoints in chromosomes 5, 6, and 14 were found by long-read nanopore sequencing. Reports on 17 males carrying CCRs with azoospermia were also reviewed. Conclusion: The extent of asynaptic regions in synaptonemal complexes during pachytene and the disruption of genes involved in male gametogenesis may cause azoospermia in CCR carriers.

Heterogeneity in conservation of multifunctional partner enzymes with meiotic importance, CDK2 kinase and BRCA1 ubiquitin ligase.

The evolution of proteins can be accompanied by changes not only to their amino acid sequences, but also their structural and spatial molecular organization. Comparison of the protein conservation within different taxonomic groups (multifunctional, or highly specific) allows to clarify their specificity and the direction of evolution. Two multifunctional enzymes, cyclin-dependent kinase 2 (CDK2) and BRCA1 ubiquitin ligase, that are partners in some mitotic and meiotic processes were investigated in the present work. Two research methods, bioinformatics and immunocytochemical, were combined to examine the conservation levels of the two enzymes. It has been established that CDK2 is a highly conserved protein in different taxonomic lineages of the eukaryotic tree. Immunocytochemically, a conserved CDK2 pattern was revealed in the meiotic autosomes of five rodent species and partially in domestic turkey and clawed frog. Nevertheless, variable CDK2 distribution was detected at the unsynapsed segments of the rodent X chromosomes. BRCA1 was shown to be highly conserved only within certain mammalian taxa. It was also noted that in those rodent nuclei, where BRCA1 specifically binds to antigens, asynaptic regions of sex chromosomes were positive. BRCA1 staining was not always accompanied by specific binding, and a high nonspecificity in the nucleoplasm was observed. Thus, the studies revealed different conservation of the two enzymes at the level of protein structure as well as at the level of chromosome behavior. This suggests variable rates of evolution due to both size and configuration of the protein molecules and their multifunctionality.

Kinase CDK2 in Mammalian Meiotic Prophase I: Screening for Hetero- and Homomorphic Sex Chromosomes.

Cyclin-dependent kinases (CDKs) are crucial regulators of the eukaryotic cell cycle. The critical role of CDK2 in the progression of meiosis was demonstrated in a single mammalian species, the mouse. We used immunocytochemistry to study the localization of CDK2 during meiosis in seven rodent species that possess hetero- and homomorphic male sex chromosomes. To compare the distribution of CDK2 in XY and XX male sex chromosomes, we performed multi-round immunostaining of a number of marker proteins in meiotic chromosomes of the rat and subterranean mole voles. Antibodies to the following proteins were used: RAD51, a member of the double-stranded DNA break repair machinery; MLH1, a component of the DNA mismatch repair system; and SUN1, which is involved in the connection between the meiotic telomeres and nuclear envelope, alongside the synaptic protein SYCP3 and kinetochore marker CREST. Using an enhanced protocol, we were able to assess the distribution of as many as four separate proteins in the same meiotic cell. We showed that during prophase I, CDK2 localizes to telomeric and interstitial regions of autosomes in all species investigated (rat, vole, hamster, subterranean mole voles, and mole rats). In sex bivalents following synaptic specificity, the CDK2 signals were distributed in three different modes. In the XY bivalent in the rat and mole rat, we detected numerous CDK2 signals in asynaptic regions and a single CDK2 focus on synaptic segments, similar to the mouse sex chromosomes. In the mole voles, which have unique XX sex chromosomes in males, CDK2 signals were nevertheless distributed similarly to the rat XY sex chromosomes. In the vole, sex chromosomes did not synapse, but demonstrated CDK2 signals of varying intensity, similar to the rat X and Y chromosomes. In female mole voles, the XX bivalent had CDK2 pattern similar to autosomes of all species. In the hamster, CDK2 signals were revealed in telomeric regions in the short synaptic segment of the sex bivalent. We found that CDK2 signals colocalize with SUN1 and MLH1 signals in meiotic chromosomes in rats and mole voles, similar to the mouse. The difference in CDK2 manifestation at the prophase I sex chromosomes can be considered an example of the rapid chromosome evolution in mammals.

Meiosis in the scorpion Tityus silvestris: new insights into achiasmatic chromosomes.

ABSTRACTAchiasmatic male meiosis in scorpions is characterized by a high frequency of gaps, asynaptic regions and multivalent associations. Here, we performed an immunocytogenetic analysis to investigate recombination, and synapsis and chromatin-remodeling events during meiosis of the scorpion Tityus silvestris. Our results demonstrate that the synaptonemal complex (SC) begins its organization in the zygotene stage and persists until metaphase I. The advancement of the synaptic process is related to the epigenetic modification histone H3 lysine 27 trimethylation (H3K27m3). The distribution and dynamics patterns of variant γH2AX and recombinase Rad51 during achiasmatic meiosis suggests formation and repair of DNA double-strand breaks (DSBs) during early stages of prophase I. The epigenetic modifications, histone H3 lysine 4 trimethylation (H3K4m3) and histone H3 lysine 9 acetylation (H3K9ac), showed a dispersed distribution along the bivalents, suggesting that transcriptional activity is maintained constitutively during prophase I. However, H3K9ac modifications are absent in constitutive heterochromatin carrying the 45S rDNA in pachytene and post-pachytene stages. Collectively, our data demonstrate that T. silvestris exhibits adaptations to the achiasmatic mode, and suggest that epigenetic modifications may act in the regulation of these mechanisms to favor the normal continuation of meiosis in this scorpion.

Synaptic behavior of Leptodactylus pentadactylus (Anura: Leptodactylidae) by immunolocalization of proteins

Most species of the genus Leptodactylus share similar karyotypes, with 2n=22 and NF=44. The species L. pentadactylus presents a multivalent in its karyotype, resulting from multiple translocations, forming a ring chromosome during meiosis I. In this study analyzed the meiotic behavior of L. pentadactylus, from Brazilian Amazonia, through immunoprotein markers. Testicular tissues of an adult male were collected and analyzed by immunofluorescence microscopy, using antibodies to detect the following meiotic proteins: SMC3, component of chromosomal axis, and responsible for cohesion between sister chromatids; ?-H2AX in a protein marker of meiotic silencing of unsynapsed chromatin (MSUC). The results showed that: in leptotene, SMC3 and ?-H2AX mark fuzzy segments throughout all the chromatin; in the zygotene; regions that start synapses are intensely marked by ?-H2AX; in turn, with the advancement of the synapse at the end of the zygotene, ?-H2AX markings expand evenly in the chromatin; in pachytene, the synapsis remains incomplete, and several asynaptic regions were noted, with ?-H2AX markings more intense on synapsed regions of chromosomes involved or not in multivalent links; in diplotene, the synaptonemal complex is disorganized, SMC3 cohesin is present on partially decondensed, chromatin, and ?-H2AX markings are present only in some regions; in diakinesis, SMC3 maintains the same pattern of diplotene, however, ?-H2AX markings are quite reduced. The results of meiotic behavior of L. pentadactylus show asynaptic axes in pachytene, which probably do not present homology with each other, corresponding to segments that suffered multiple rearrangements. SMC3 pattern and reduction of ?-H2AX markings in diplotene, suggest decondensation of chromatin, with reactivation of transcription in chromosomal handles. The absence of ?-H2AX markings in diakinesis show that the rearranged chromosomes of L. pentadactylus do not compromise the spermatogenesis of the animal, ensuring its meiotic dynamic and fertility.

Dual mechanism of chromatin remodeling in the common shrew sex trivalent (XY 1Y 2).

Here we focus on the XY1Y2 condition in male common shrew Sorex araneus Linnaeus, 1758, applying electron microscopy and immunocytochemistry for a comprehensive analysis of structure, synapsis and behaviour of the sex trivalent in pachytene spermatocytes. The pachytene sex trivalent consists of three distinct parts: short and long synaptic SC fragments (between the X and Y1 and between the X and Y2, respectively) and a long asynaptic region of the X in-between. Chromatin inactivation was revealed in the XY1 synaptic region, the asynaptic region of the X and a very small asynaptic part of the Y2. This inactive part of the sex trivalent, that we named the ‘head’, forms a typical sex body and is located at the periphery of the meiotic nucleus at mid pachytene. The second part or ‘tail’, a long region of synapsis between the X and Y2 chromosomes, is directed from the periphery into the nucleus. Based on the distribution patterns of four proteins involved in chromatin inactivation, we propose a model of meiotic silencing in shrew sex chromosomes. Thus, we conclude that pachytene sex chromosomes are structurally and functionally two different chromatin domains with specific nuclear topology: the peripheral inactivated ‘true’ sex chromosome regions (part of the X and the Y1) and more centrally located transcriptionally active autosomal segments (part of the X and the Y2).

Differential cohesin loading marks paired and unpaired regions of platypus sex chromosomes at prophase I

Cohesins are vital for chromosome organisation during meiosis and mitosis. In addition to the important function in sister chromatid cohesion, these complexes play key roles in meiotic recombination, DSB repair, homologous chromosome pairing and segregation. Egg-laying mammals (monotremes) feature an unusually complex sex chromosome system, which raises fundamental questions about organisation and segregation during meiosis. We discovered a dynamic and differential accumulation of cohesins on sex chromosomes during platypus prophase I and specific reorganisation of the sex chromosome complex around a large nucleolar body. Detailed analysis revealed a differential loading of SMC3 on the chromatin and chromosomal axis of XY shared regions compared with the chromatin and chromosomal axes of asynapsed X and Y regions during prophase I. At late prophase I, SMC3 accumulation is lost from both the chromatin and chromosome axes of the asynaptic regions of the chain and resolves into subnuclear compartments. This is the first report detailing unpaired DNA specific SMC3 accumulation during meiosis in any species and allows speculation on roles for cohesin in monotreme sex chromosome organisation and segregation.

Homomorphic Sex Chromosomes and the Intriguing Y Chromosome of Ctenomys Rodent Species (Rodentia, Ctenomyidae)

Unlike the X chromosome, the mammalian Y chromosome undergoes evolutionary decay resulting in small size. This sex chromosomal heteromorphism, observed in most species of the fossorial rodent Ctenomys, contrasts with the medium-sized, homomorphic acrocentric sex chromosomes of closely related C. maulinus and C. sp. To characterize the sequence composition of these chromosomes, fluorescent banding, self-genomic in situ hybridization, and fluorescent in situ hybridization with an X painting probe were performed on mitotic and meiotic plates. High molecular homology between the sex chromosomes was detected on mitotic material as well as on meiotic plates immunodetected with anti-SYCP3 and anti-γH2AX. The Y chromosome is euchromatic, poor in repetitive sequences and differs from the X by the loss of a block of pericentromeric chromatin. Inferred from the G-banding pattern, an inversion and the concomitant prevention of recombination in a large asynaptic region seems to be crucial for meiotic X chromosome inactivation. These peculiar findings together with the homomorphism of Ctenomys sex chromosomes are discussed in the light of the regular purge that counteracts Muller's ratchet and the probable mechanisms accounting for their origin and molecular homology.

Synapsis, recombination, and chromatin remodeling in the XY body of armadillos

Three xenarthrans species Chaetophractus villosus, Chaetophractus vellerosus, and Zaedyus pichiy have been used for the analysis of the structure, behavior, and immunochemical features of the XY body during pachytene. In all these species, the sex chromosomes form an XY body easily identifiable in thin sections by the special and regular packing of the chromatin fibers of the internal region of the XY body ("differential" regions) and those of the peripheral region (synaptic region). Spermatocyte spreads show a complete synapsis between the X- and the Y-axis, which lasts up to the end of pachytene. From the early pachytene substages to the late ones, the X-axis develops prominent branches, which in late pachytene span the synaptic region. Synapsis is regular as shown by SYCP1 labeling. Axial development is followed by SYCP3 labeling and in the asynaptic region of the X-axis by BRCA1. Gamma-H2AX labels exclusively the differential (asynaptic) region of the X chromosome. A single focus is labeled by MLH1 in the synaptic region. The location of this MLH1 focus spans from 0.3 to 1.6 μm from the telomere in the analyzed xenarthrans, covering approximately half of the Y-axis length. It is concluded that xenarthrans, as basal placental mammals, harbor the largest pseudoautosomal regions of presently analyzed mammals, and shows the typical features of meiotic sex chromosome inactivation (MSCI).

The role of asynapsis in human spermatocyte failure

The basic molecular mechanisms by which chromosomal rearrangements in heterozygous state produce spermatogenic disturbances are poorly understood. Testicular biopsies from five patients - one carrier of a Robertsonian translocation rob t(13;14), two carriers of two different Y-autosome translocations, a t(Y;6) and a t(Y;11), one carrier of a reciprocal translocation t(3;13) and one carrier of a heterochromatin duplication in chromosome 9 - were processed for histopathological analysis, electron microscopy and fluorescent immunolocalization of meiotic proteins. In all the patients, the asynaptic regions during pachytene are labelled by BRCA1 and retained RAD51 foci. The variant histone γ-H2AX is located on the chromatin domains of the asynaptic regions and the XY body. In contrast, these meiotic proteins are absent in those chromosomal segments that are non-homologously synapsed. The present observations on five new cases and a review of recent studies show that the common features shared by all these cases are the abnormal location of some meiotic proteins and the presence of transcriptionally silenced chromatin domains on asynaptic regions. The frequent association of these silenced regions with the XY body and the rescue of spermatocyte viability through non-homologous synapsis are also shared by all these carriers. A passive, random mechanism of clustering of asynaptic regions with the XY body is suggested.

Molecular and cytogenetic evidence of three sibling species of the Anopheles barbirostris Form A (Diptera:Culicidae) in Thailand

Nine isoline colonies of Anopheles barbirostris Form A, derived from individual isofemale lines from Chiang Mai, Phetchaburi, and Kanchanaburi, were established in our insectary at Chiang Mai University. All isolines shared the same mitotic karyotype (X(1), X(2), Y(1)). Molecular analysis of deoxyribonucleic acid (DNA) sequences and polymerase chain reaction (PCR) products of ITS2, COI, and COII regions revealed three distinct groups: A1 (Chiang Mai), A2 (Phetchaburi), and A3 (Kanchanaburi). Crossing experiments among the three groups exhibited strong reproductive isolation, producing low and/or non-hatched eggs, and inviable and/or abnormal development of the reproductive system of F(1)-progenies. Asynaptic regions along the five polytene chromosome arms of F(1)-hybrid larvae clearly supported the existence of three sibling species within A. barbirostris Form A, provisionally named species A1, A2, and A3.

The asynaptic chromatin in spermatocytes of translocation carriers contains the histone variant γ-H2AX and associates with the XY body

The close apposition of multivalents with the XY body has been repeatedly described in heterozygous carriers of chromosomal rearrangements. Because in many of these carriers spermatogenesis is deeply disturbed at the spermatocyte level, the association of autosomal chromatin with the XY body may impair the spermatocyte life. Testicular biopsies from three men carriers of three different chromosomal rearrangements have been analysed by electron microscopy (EM) and immunolocalization of meiotic proteins. There is an ordered transition from isolated multivalents at early pachytene to XY body association in late pachytene, as shown in a carrier of a rob t(13;14) translocation by EM and in a reciprocal translocation t(9;14) carrier by immunofluorescence. The non-synapsed ends of the quadrivalent show BRCA1 located on the axes and the variant histone gamma-H2AX located on the chromatin. The area covered by gamma-H2AX increases with the association of the asynaptic ends with the XY body in the t(9;14) carrier, and the area covered with gamma-H2AX in the t(Y;15) carrier is larger than that of the XY body of controls. The affinity between the inactive XY body and asynaptic regions of multivalents is given a material basis, and transcriptional inactivation is probably shared by these two chromatin types.

Infertility and aneuploidy in mice lacking a type IA DNA topoisomerase III beta.

We report that disruption of the mouse TOP3 beta gene encoding DNA topoisomerase III beta, one of the two mammalian type IA DNA topoisomerases, leads to a progressive reduction in fecundity. The litter size in crosses of top3 beta(-/-) mice decreases over time and through successive generations, and this decrease seems to reflect embryonic death rather than impaired fertilization. These observations are suggestive of a gradual accumulation of chromosomal defects in germ cells lacking DNA topoisomerase III beta, and this interpretation is supported by the observation of a high incidence of aneuploidy in the spermatocytes of infertile top3 beta(-/-) males. Cytogenetic examination of spermatocytes of wild-type mice also indicates that DNA topoisomerase III beta becomes prominently associated with the asynaptic regions of the XY bivalents during pachytene, and that there is a time lag between the appearance of chromosome-bound DNA topoisomerase III beta and Rad51, a protein known to be involved in an early step of homologous recombination. We interpret these findings, together with the known mechanistic characteristics of different subfamilies of DNA topoisomerases, in terms of a specific role of a type IA DNA topoisomerase in the resolution of meiotic double-Holliday junctions without crossing over. This interpretation is most likely applicable to mitotic cells as well and can explain the universal presence of at least one type IA DNA topoisomerase in all organisms.

Karyotypes of four Diamesinae species (Diptera) from Russia

The first description of the karyotype of four species of theDiamesinae subfamily is presented. The diploid chromosome number was found to be 8 in all the studied species. Judging from the banding pattern, the karyotypes ofPseudodiamesa (Pagastia) orientalis Tshern. andPseudodiamesa (Pagastia) lanceolata are very similar.P. lanceolata differs fromP. orientalis in the presence of two homozygous inversions, of which one involves about half of arm E, and the other located in arm D.Lappodiamesa willasseni Makar. et Kerk. andSympotthastia repentina Makar. are the first karyologically described representatives of the two genera. The karyotype ofL. willasseni has a large spherical chromosome. The karyotypes ofL. willasseni andS. repentina show a characteristic asynaptic region on the polytene chromosomes which is more prominent inS. repentina.

Chromosome 1 in crested and marbled newts (Triturus)

The heteromorphic chromosomes 1 of Triturus cristatus carnifex and T. marmoratus were studied in mitotic metaphase after staining with the Giemsa C-banding technique and with the fluorochromes, DAPI (AT-specific) and mithramycin (GC-specific). They were also examined in the lampbrush form under phase-contrast before fixation and after fixation and staining with Giemsa. Chromosomes 1 of T.c. carnifex are asynaptic and achiasmatic throughout most of their long arms. They are also heteromorphic in most of their long arms for the patterns of Giemsa and fluorochrome staining and the distribution of distinctive lampbrush loops. The heteromorphic regions correspond to the regions that are asynaptic and achiasmatic. They stain more strongly with mithramycin and more weakly with DAPI than the remainder of the chromosomes, signifying that their DNA is relatively rich in GC. The patterns of staining with Giemsa and fluorochromes and the distributions of distinctive lateral loops vary from one animal to another in the same species and even in the same population. The asynaptic and achiasmatic regions of chromosomes 1 in T. marmoratus extend throughout the whole of the long arms and well beyond the heterochromatic region. Chiasmata form only in the short arm and occasionally in the short euchromatic segment at the tip of the long arms. The staining patterns of chromosomes 1 in T. marmoratus differ from those in T.c. carnifex although, like carnifex, their DNA is relatively GC-rich. The chromosomes 1 of T. marmoratus are more submetacentric than those of T.c. carnifex. In T. marmoratus chromosome 1B is about 12% shorter than 1A. There is a short paracentric inversion heterozygosity in the long arm of chromosome 1B in T. marmoratus which probably accounts for the lack of chiasmata in the euchromatin that separates the centromere from the start of the heterochromatin. In both carnifex and marmoratus, embryos that are homomorphic for chromosome 1 arrest and die at the late tailbud stage of development. The same applies to F1 hybrid embryos T.c. carnifex x T. marmoratus, and this has permitted identification of chromosomes 1A and 1B in both species. There is no correspondence between patterns of Giemsa or fluorochrome staining of the heteromorphic regions of chromosome 1 and any feature of the lampbrush chromosomes. However, the short euchromatic ends of the long arms of chromosomes 1 in both species are distinguished in the lampbrush form by a series of uniformly small loops of fine texture associated with very small chromomeres. The Giemsa C-staining patterns of both chromosomes 1A and 1B are different in each of the four subspecies of T. cristatus. T.c. karelinii stands out by having unusually large masses of Giemsa C-staining centromeric heterochromatin on all but 1 of its 12 chromosomes. A scheme is proposed for the evolution of chromosome 1 in T. cristatus and T. marmoratus, based on all available cytological and molecular data.

Meiosis of trisomy 21 in the human pachytene oocyte. Behaviour of the supernumerary chromosome, identification of chromomere sequence and numerous sub-bands.

Association modalities of the three 21 chromosomes were studied during pachytene in three trisomy 21 fetuses whose chromosomal constitution was identified following amniocentesis. -- Three classes of images were observed: a trivalent, a trivalent presenting an important asynaptic region of the long arm, and a bivalent accompanied by a univalent. Such behaviour is analagous to that observed in all trisomic organisms. -- We have been able to establish the sequence of chromomeres, whose number varies from 9 to 14 according to the state of contraction in the 21 chromosome. Each band is thus subdivided into several sub-bands: at maximal elongation 2 sub-bands for band p11, 4 for q21 and 3 for q222. In addition, the interchromomeric clear bands q221 and q223 are also subdivided by the presence of a very small chromomere. In this way, the G-bands visible on mitotic metaphase chromosomes result from the compression together of several chromomeres whose individuality disappears as chromosomal condensation increases with progression of prophase.

The Salivary Gland Chromosomes ofTelmatoscopus Albipunctatus(Williston) (Diptera: Psychodidae)

SUMMARYThe salivary gland cells of Telmatoscopus albipunctatus have six polytene chromosomes variously connected and without any common chromocentre.Heterochromatic material, perhaps in part of sexual orgin, is present at the ends of the chromosomes as well as in single intercalary bands.Polytene chromosomes have frequent asynaptic regions and several heterozygous bands and puffs.The probable meaning of these findings is discussed.

Differential DNA synthesis in homologous regions of hybrid polytenic chromosomes (Anopheles atroparvus x A. labranchiae)

Differential DNA synthesis is demonstrated in asynaptic regions of the polytenic chromosomes of the Anopheles atroparvus x A. labranchiae hybrid. This differential synthesis is present both in homologous segments with different banding patterns and in morphologically identical segments. Each differential synthesis appears to be related to a specific portion of the replication cycle and due to the fact that one of the two homologues requires a shorter period of time for its duplication.

Meiosis in translocation heterozygotes in the mosquito Culex pipiens.

Adult Culex pipiens males irradiated with both X-rays and neutrons were crossed to untreated females and F1-egg rafts were checked for dominant lethality. F1-progenies were outcrossed with normal individuals in order to obtain lines with inherited semisterility. From a total of 120 lines that showed a certain amount of sterility 12 lines were studied cytologically. 10 lines showed reciprocal chromosome exchanges.—At late pachytene and diplotene cross configurations with large asynaptic regions at the center of the cross are obligatory. Bivalents, chains of three, chains of four, and ring configurations are present at metaphase and anaphase I. The different frequencies of the occurrence of such multiples are dependent on the chromosomes involved in the exchange, the length of the pairing segments and the chiasma frequencies in these segments. Chiasma frequency in the interstitial segments is reduced by means of chiasma interference over the centromere and by asynapsis near the breakage points. — Alternate, adjacent-1- and adjacent-2-distributions are present to a different extent. Alternate distribution is most, adjacent-2-distribution least frequent. — The role of translocations and the probability of their becoming effective in pest eradication programs is discussed.