Chromosomal variability of the field mouse Apodemus agarius (Rodentia, Muridae)

Chromosome sets of 114 Apodemus agrarius mice from 29 localities in Moldova, Ukraine, Siberia, and Far East were studied by means of G-, C-, and NOR-banding. In all populations studied, the Y chromosome was shown to be a medium-size acrocentric chromosome consisting of heterochromatin. Chromosome polymorphism observed in populations from Primorskii krai concerned (1) the morphology of the first two autosome pairs (variants A/A, A/ST, and ST/ST), (2) the number of metacentric chromosomes (from 6 to 8), and (3) heterochromatin localization in the pericentromeric regions of two metacentric chromosome pairs. A karyotype with an additional heterochromatic microchromosome found in all the metaphases studied was described in one mouse from a locality of western Primorye that has not been studied previously. In the karyotype of 15 mice from four populations of Primorye, the pool of nucleolus organizer regions is distributed over three autosome pairs rather than over four, as is the case A. agrarius from Europe. Based on the analysis of literature sources and our own data, the problem of chromosome polymorphism in the field mouse is discussed.     

Changes in NOR activity pattern in the presence of supernumerary heterochromatin in the grasshopper Eyprepocnemis plorans

Nucleolus organizer region (NOR) activity was analysed in four types of males of the grasshopper Eyprepocnemis plorans, possessing two kinds of supernumerary heterochromatin: a B chromosome and a supernumerary chromosome segment proximally located on the smallest autosome (S11). In males lacking extra heterochromatin, the four active NORs located on the S9, S10, S11, and X chromosomes showed independent activity patterns, but several kinds of dependence appeared in the presence of supernumerary heterochromatin. Furthermore, temporal changes in NOR activity were observed during the first 2 weeks of adult life in standard males but not in males carrying supernumerary heterochromatin. It is suggested that all these effects are related to the DNA content of both types of extra heterochromatin.     

Chromosome studies in the red howler monkey, Alouatta seniculus stramineus (Platyrrhini, Primates): description of an X1X2Y1Y2/X1X1X2X2 sex-chromosome system and karyological comparisons with other subspecies

In the red howler monkey, Alouatta seniculus stramineus (2n = 47, 48, or 49), variations in diploid chromosome number are due to different numbers of microchromosomes. Males exhibit a Y;autosome translocation involving the short arm of an individual biarmed autosome. Consequently, the sex-chromosome constitution in the male is X1X2Y1Y2, with X1 representing the original X chromosome, X2 the biarmed autosome (No. 7), Y1 the Y;7p translocation product, and Y2 the acrocentric homolog of 7q. In the first meiotic division, a quadrivalent with a chain configuration can be observed in spermatocytes. Females have an X1X1X2X2 sex-chromosome constitution. Chromosome heteromorphisms were observed in pair 13, due to a pericentric inversion, and pair 19, due to the presence of constitutive heterochromatin. Microchromosomes, which varied in number between individuals, were also heterochromatic. NOR-staining was observed at two separate sites on a single chromosome pair (No. 10). A comparison of A.s. stramineus with A.s. macconnelli shows that these two subspecies have identical diploid chromosome numbers (47, 48, or 49), again due to a varying number of microchromosomes, and that they share a similar sex-chromosome constitution. Their karyotypes, however, are not identical, but can be derived from each other by a reciprocal translocation. Further comparisons with other A. seniculus subspecies reported in the literature indicate that this taxon is not karyologically uniform and that substantial chromosome shuffling has occurred between populations that have been considered to be subspecies by taxonomic criteria based on their morphometric attributes.     

Polymorphic patterns of heterochromatin distribution in guinea pig chromosomes

The chromosome complement and patterns of heterochromatin distribution (as demonstrated by the DNA d-r method) were studied from three different guinea pigs. Karyotype analyses showed that one of the females had a heteromorphic sex pair formed by a submetacentric X chromosome and a subterminal X chromosome originated by a shortening of the short arm (x-chromosome). The heterochromatin was mainly found in the pericentromeric areas of the autosomes and X chromosomes and in the short arm of pair 7. The Y chromosome exhibited a degree of heterochromatinization different from that of pericentromeric areas.—The analysis of the heterochromatin distribution in the X chromosomes showed that the smaller size of the heteromorphic x-chromosoine was probably due to a lack of heterochromatin in its short arm. Moreover, two out of the three animals studied had a heteromorphic pattern of heterochromatinization in the pair 21 characterized by heterochromatinization of the pericentromeric area in one chromosome and almost complete heterochromatinization of the other homologue.—It is suggested that most of the heterochromatin disclosed by the DNA d-r method is formed by repetitious DNA; and that the Y chromosome and perhaps some autosome regions in guinea pigs are formed by a type of heterochromatin with properties different from those of the constitutive and facultative heterochromatin (intermediate heterochromatin).Supported in part by NIH Grant 5-501-RR05672-02 and by NIH contract 70-2299.     

Chromosomal polymorphism of Rattus rattus (Linnaeus, 1758) (rodentia: muridae) in Central Anatolia

In this study, conventionally stained, C- and Ag-NOR banded karyotypes of Rattus rattus from Central Anatolia are presented. The karyotype of the specimens from Ankara and (Cankiri provinces consist of 2n = 38, NF = 60 and NFa = 58 while the karyotype of Kirikkale specimens consist of 2n = 38 and NFa = 59 due to a heteromorphic autosome pair. The X is a large to medium sized acrocentric and the Y chromosome is a small acrocentric in all examined specimens. Constitutive heterochromatin is located in the centromeric regions of all pairs of autosomes and the X chromosome. Nucleolar organizer regions (NORs) are located only in 3 autosome pairs.     

Adding the heterochromatic YL arm to an X chromosome reduces reproductive fitnesses in Drosophila melanogaster: implications for the evolution of rDNA, heterochromatin, and reproductive isolation

For X-Y exchange to be of importance in the coevolution of X and Y rDNA, there must be a mechanism to maintain cytologically normal X chromosomes in the face of continual infusions of X.YL chromosomes produced by X-Y exchanges. Replicated populations were founded with different frequencies of isogenic X and X.YL chromosomes. The X.YL chromosome declined in frequency over time in all lines. Relative fitnesses, estimated from chromosome frequency trajectories, were 0.40, 1.01, and 1.0 for X.YL/X.YL, X.YL/X, and X/X females and 0.75 and 1.0 for X.YL/Y and X/Y males, respectively. The equilibrium frequency for the X.YL chromosome due to the balance between X-Y exchange and selection was predicted to be 4-16 x 10(-4). The results strengthen the evidence for the involvement of X-Y exchange in the coevolution of X and Y rDNA arrays. Conditions for the evolution of reproductive isolation by sex-chromosome translocation are much less probable than previously supposed since the X.YL translocation chromosome is at a selective disadvantage to cytologically normal X chromosomes. Additional heterochromatin was not neutral but was only deleterious beyond a threshold, as one dose of the heterochromatic XL arm did not reduce female reproductive fitness, but two doses did.     

Sex chromosome-autosome translocations in the leaf-nosed bats, family Phyllostomidae. I. Mitotic analyses of the subfamilies Stenodermatinae and Phyllostominae

Mitotic analyses using RBA- and C-banding were performed on Stenodermatine bats with X-autosome (XY1Y2) and X- and Y- autosome (neo-XY) translocations. RBA-banded metaphases of females revealed differential replication of the inactive X chromosome. An early replicating band comprises the short arm of the X, and an intermediate replicating band is located interstitially on the long arm. The early replicating short arm has a homologous counterpart either in the form of a free autosome (the Y2) or as part of the Y. Both the "autosomal" short arm of the X and its homologue fused to the Y are C-band negative and behave autonomously from the remainder of the sex chromosomes. They are separated from X and Y chromatin by centromeric heterochromatin which presumably acts as a barrier. The intermediate replicating region of the long arm of the X is also present in the subfamily Phyllostominae. In both subfamilies this region lacks a homologous counterpart. However, it may also represent a translocated autosome which, unlike the short arm of the X, is not separated from the inactive X by centromeric heterochromatin. Its intermediate replication time may represent a retarded replication due to its juxtaposition to late replicating X chromatin. These data are discussed in light of the theory of the evolution of sex chromosome heteromorphism, specifically as it applies to mammals.     

Recombinogenic effects of suppressors of position-effect variegation in Drosophila

Compact chromatin structure, induction of gene silencing in position-effect variegation (PEV), and crossing-over suppression are typical features of heterochromatin. To identify genes affecting crossing-over suppression by heterochromatin we tested PEV suppressor mutations for their effects on crossing over in pericentromeric regions of Drosophila autosomes. From the 46 mutations (28 loci) studied, 16 Su(var) mutations of the nine genes Su(var)2-1, Su(var)2-2, Su(var)2-5, Su(var)2-10, Su(var)2-14, Su(var)2-15, Su(var)3-3, Su(var)3-7, and Su(var)3-9 significantly increase in heterozygotes or by additive effects in double and triple heterozygotes crossing over in the ri-p(p) region of chromosome 3. Su(var)2-2(01) and Su(var)2-14(01) display the strongest recombinogenic effects and were also shown to enhance recombination within the light-rolled heterochromatic region of chromosome 2. The dominant recombinogenic effects of Su(var) mutations are most pronounced in proximal euchromatin and are accompanied with significant reduction of meiotic nondisjunction. Our data suggest that crossing-over suppression by heterochromatin is controlled at chromatin structure as well as illustrate the possible effects of heterochromatin on total crossing-over frequencies in the genome.     

白颊长臂猿染色体的研究

本文对我国云南南部的白须长臂猿（Ｈ．ｌｅｕｃｏｇｅｎｙｓ）染色体的Ｇ带、Ｃ带、晚复制带及Ａｇ－ＮＯＲｓ进行了较为详细的研究。它的２ｎ＝５２,核型公式为４４（Ｍ或ＳＭ）＋６（Ａ）,ＸＹ（Ｍ,Ａ）。Ｃ带表明一些染色体着丝点Ｃ带弱化;有的染色体出现插入的和端位的Ｃ带;Ｘ染色体两臂有端位Ｃ带,Ｙ染色体是Ｃ带阳性和晚复制的。Ａｇ－ＮＯＲｓ的数目,雌体有４个,雄体有５个,Ｙ染色体上具ＮＯＲ。本文对白颊长臂猿与其它长臂猿间的亲缘关系、核型进化的可能途径进行了讨论。     

Expression of Saccharomyces cerevisiae MATa and MAT alpha enhances the HO endonuclease-stimulation of chromosomal rearrangements directed by his3 recombinational substrates

Radiation resistance in Saccharomyces cerevisiae is greater in a/alpha diploids than in aa or alpha alpha diploids, and higher levels of radiation resistance correlates with more mitotic recombination. Specifically, we investigated whether the stimulation of directed translocations, inversions, and unequal sister chromatid exchanges (SCEs) by HO endonuclease-induced double-strand breaks (DSBs) is enhanced in a/alpha cells. These rearrangements result from mitotic recombination between two truncated his3 genes, his3-delta 5' and his3-delta 3'::HOcs, positioned on non-homologous chromosomes or positioned in juxtaposition on the same chromosome in inverted or direct orientation. Mitotic recombination was initiated by HO endonuclease-induced DSBs at the HO cut site (HOcs) located at his3-delta 3'::HOcs, and His+ recombinants were selected. In MATa-inc haploid strains, which do not switch mating-type, the DSB reduced viability, relative to undamaged cells, and increases the frequency of His+ recombinants containing translocations to 2.4 x 10(-4) (seven-fold), SCEs to 5.4 x 10(-4) (five-fold), and inversions to 1.8 x 10(-3) (six-fold). Compared to a haploids, DSB-stimulated frequencies in a/alpha haploids were three-fold higher for translocations, two-fold higher for SCEs, and ten-fold higher for inversions; however DSB-induced lethality was greater in a/alpha haploids. Compared to aa diploids, DSB-stimulated frequencies of translocations and viability after chromosome cleavage were greater in a/alpha diploids. We suggest that heterozygosity at MAT may elevate the frequency of DSB-initiated reciprocal exchange events in both haploid and diploid cells, but may only increase viability after chromosome cleavage in diploid cells.     

The origin of mitotic sex-chromosome association in the brush-tailed possum, Trichosurus vulpecula (marsupalia:phalangeridae)

Nonrandom associations between the sex chromosomes of the brush-tailed possum, Trichosurus vulpecula, were found to be due to association of nucleolar organizer regions (NOR's) on the X and Y chromosomes. NOR association was also observed between an autosome and the X chromosome. These findings, based on silver staining, are in contrast to the report of MURRAY (1977), who observed sex-chromosome association in this animal and indicated that these nonrandom associations may reflect an association between heterochromatic regions during interphase. We observed only two pairs of NOR's per cell in this animal, one autosomal and one on the sex chromosomes, rather than the several such regions observed by MURRAY, who used an N-banding technique. We discuss the problem of nonhomologous chromosome association in mammalian cells as influenced by heterochromatin and NOR's and find little support for nonhomologous chromosome associations at mitotic metaphase due to heterochromatin association.     

High mutability in rye (Secale cereale L.).

Analysis of the rye cultivar Ailés of several descents derived from crosses between plants carrying specific genotypes and/or chromosome constitutions resulted in the detection of high chromosome (2.05 x 10(-2)) and gene (9.3 x 10(-3)) mutation frequencies. The existence of a transposon system responsible for this instability is suggested.     

The chromosomes of tufted deer (Elaphodus cephalophus)

Mitotic and meiotic chromosome preparations of the tufted deer (Elaphodus cephalophus) were studied to elucidate the sex-chromosomal polymorphism evidenced by this species. Females had 2n = 46 or 47 chromosomes, whereas males had 2n = 47 or 48 chromosomes. An X;autosome translocation was identified by synaptonemal complex analysis of spermatocytes at pachytene and confirmed by the presence of a trivalent at diakinesis/metaphase I. The present work, in combination with earlier observations by others, indicates that E. cephalophus possesses a varied X-chromosome morphology involving an X;autosome translocation and addition of varying amounts of heterochromatin. It is speculated that sex-chromosome polymorphism may be responsible for the observed differences in diploid chromosome number of tufted deer.     

High-frequency phage-mediated gene transfer among Escherichia coli cells, determined at the single-cell level

Recent whole-genome analysis suggests that lateral gene transfer by bacteriophages has contributed significantly to the genetic diversity of bacteria. To accurately determine the frequency of phage-mediated gene transfer, we employed cycling primed in situ amplification-fluorescent in situ hybridization (CPRINS-FISH) and investigated the movement of the ampicillin resistance gene among Escherichia coli cells mediated by phage at the single-cell level. Phages P1 and T4 and the newly isolated E. coli phage EC10 were used as vectors. The transduction frequencies determined by conventional plating were 3x10(-8) to 2x10(-6), 1x10(-8) to 4x10(-8), and <4x10(-9) to 4x10(-8) per PFU for phages P1, T4, and EC10, respectively. The frequencies of DNA transfer determined by CPRINS-FISH were 7x10(-4) to 1x10(-3), 9x10(-4) to 3x10(-3), and 5x10(-4) to 4x10(-3) for phages P1, T4, and EC10, respectively. Direct viable counting combined with CPRINS-FISH revealed that more than 20% of the cells carrying the transferred gene retained their viabilities. These results revealed that the difference in the number of viable cells carrying the transferred gene and the number of cells capable of growth on the selective medium was 3 to 4 orders of magnitude, indicating that phage-mediated exchange of DNA sequences among bacteria occurs with unexpectedly high frequency.     

Obervations on the Induction of Position Effect Variegation of Euchromatic Genes in Drosophila Melanogaster

In the T(1;2)dor(var7) translocation, the 1A-2B7-8 segment of the X chromosome is brought to the vicinity of 2R-chromosome heterochromatin resulting in position effect variegation of dor, BR-C and more distal genes, as well as compaction of chromatin in this segment. By irradiation of T(1;2)dor(var7), nine reversions (rev) to a normal phenotype were recovered. In two cases (rev27, rev226), the 1A-2B7-8 section is relocated to the 19A region of the X chromosome, forming free duplications (1A-2B7-8/19A-20F-X-het). Modifiers of position effect do not change the normal expression of the BR-C and dor genes in these duplications. In five reversions (rev3, rev40, rev60, rev167, rev175), free duplications have formed from the 1A-2B7-8 fragment and X chromosome heterochromatin. In these rearrangements, modifiers of position effect (low temperature, removal of Y and 2R-chromosome heterochromatin and a genetic enhancer (E-var(3)201) induce position-effect again. Two reversions (rev45 and rev110) are associated with additional inversions in the original dor(var7) chromosomes. The inversions relocate part of the heterochromatin adjacent to the 1A-2B7-8 section into new positions. In T(1;2)dor(rev45), position-effect is seen in the 2B7-8-7A element as compaction spreading from 2B7-8 proximally in some cases as far as the 5D region. Thus, in rev45 the pattern of euchromatin compaction is reciprocal to that of the initial dor(var7) strain. Apparently, it is due to the same variegation-evoking center near the 2R centromere in both cases. In all nine revertants, weakening or complete disappearance of the position-effect is observed despite retention of the 20- kb heterochromatic segment adjacent to the 1A-2B7-8 region. Thus, a 20-kb heterochromatic sequence does not inactivate euchromatin joined to it.     

Translocation and amplification of an X-chromosome DNA repeat in inbred strains of mice.

A 9-kb repetitive DNA fragment (70-38) located near the centromere of the mouse X chromosome is amplified and translocated to an autosome in different inbred strains of mice. In situ hybridization and hybrid cell studies showed that probe 70-38 is located only on the X chromosome in mouse strains A/J, AKR/J, BALB/cJ, CBA/J, C3H/HeJ, C57BL/6J, DBA/2J and SWR/J. However, in four other mouse strains the DNA sequence is found near the centromere of an autosome in addition to the X chromosome. This autosome differs among the mouse strains (chromosome 11 in C57BL/10J or ScSn, chromosome 13 in NZB/B1NJ and chromosome 17 in SJL/J and PO). In those strains where the repeated sequence is located on an autosome, it has been amplified to about 100 copies. Restriction enzyme digestion patterns suggest a common structure for 70-38 sequences in the different strains. The changes in copy number, restriction enzyme digestion patterns, and chromosomal location of 70-38 reflect a rapid genomic evolution inbred mouse strains.     

Banding pattern analysis of initial structural chromosome alterations induced by n-methyl-n'-nitro-n-nitrosoguanidine in Syrian hamster cells

Cultured secondary Syrian hamster embryo cells exposed to 0.5 N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) microgram/ml medium exhibited chromatid type of aberrations consisting of gaps, breaks and exchanges. Although no specific chromosome or chromosome segment was preferentially affected, chromosomes belonging to the larger groups tended to more often involved. G-band analysis demonstrated that 80% of the lesions occurred in negative bands, 9% involved the centromere, 3% were on non-banded heterochromatin, and approximately 8% of the lesions could not be definitely categorized by G-band analysis. Whether the lesions occur at positive bands or at the interface between negative and positive bands is difficult to discern by the G-band resolution. The Y chromosome compared to autosomes of similar size rarely had lesions. X chromosome damage was found in both the euchromatic and heterochromatic arms. However, both sex chromosomes, as well as an autosome (E20) which is heterochromatic on its long arm, were not found joined to the chromatids of other chromosomes, further emphasizing that chromosomes with large heterochromatic areas are isolated in terms of chromatid exchange events. The analysis of MNNG induced chromosome damage indicates that the negative bands are the primary site of damage and points of exchange.     

Karyotyp und Heterochromatinmuster des rumänischen Hamsters (Mesocricetus newtoni)

In the Romanian hamster (2n=38) a number of whole chromosome arms is heterochromatic. This offers the opportunity to test the effect of some recently developed differential staining techniques upon heterochromatin. It is shown that the late replicating segments are stained by the C-banding technique. A method for exclusively demonstrating centromeric heterochromatin is described. With this, only 8 autosome pairs and the X-chromosome show centric heterochromatin. There is a good agreement between the multiple banding pattern produced by fluorescent and Giemsa stain.

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Stipendiat der Alexander-von-Humboldt-Stiftung.     

The Genetic Analysis of Distributive Segregation in Drosophila Melanogaster. I. Isolation and Characterization of Aberrant X Segregation (Axs), a Mutation Defective in Chromosome Partner Choice

We describe the isolation and characterization of Aberrant X segregation (Axs), a dominant female-specific meiotic mutation. Although Axs has little or no effect on the frequency or distribution of exchange, or on the disjunction of exchange bivalents, nonexchange X chromosomes undergo nondisjunction at high frequencies in Axs/+ and Axs/Axs females. This increased X chromosome nondisjunction is shown to be a consequence of an Axs-induced defect in distributive segregation. In Axs-bearing females, fourth chromosome nondisjunction is observed only in the presence of nonexchange X chromosomes and is argued to be the result of improper X and fourth chromosome associations within the distributive system. In XX females bearing a compound fourth chromosome, the frequency of nonhomologous disjunction of the X chromosomes from the compound fourth chromosome is shown to account for at least 80% of the total X nondisjunction observed. In addition, Axs diminishes or ablates the capacity of nonexchange X chromosomes to form trivalents in females bearing either a Y chromosome or a small free duplication for the X. Axs also impairs compound X from Y segregation. The effect of Axs on these segregations parallels the defects observed for homologous nonexchange X chromosome disjunction in Axs females. In addition to its dramatic effects on the X chromosome, Axs exerts a similar effect on the segregation of a major autosome. We conclude that Axs defines a locus required for proper homolog disjunction within the distributive system.