Translocations in DICTYOSTELIUM DISCOIDEUM

Fourteen translocations of independent origin were identified in Dictyostelium discoideum on the basis of segregation anomalies of diploids heterozygous for these chromosome rearrangements, all of which led to the cosegregation of unlinked markers. Many of these translocations were discovered in strains mutagenized with MNNG or in strains carrying mutations affecting DNA repair; however, spontaneous translocations were also obtained. Haploid mitotic recombinants of the rearranged linkage groups were produced from diploids heterozygous for the translocations at frequencies of up to 5% of viable haploid segregants; this is at least a ten-fold higher frequency than that seen with diploids not heterozygous for translocations (approximately 0.1%). These haploid recombinants included both translocated and nontranslocated strains. The T354(II, VII) translocation and possibly the T357(IV, VII) translocation reduce the chromosome number to n = 6; haploids carrying 11 other translocations all have karyotypes with n = 7. Genetic characterization of the T357(IV, VII) translocation showed that the bwnA and whiC loci normally found on linkage group IV were physically linked to the linkage group VII loci couA, phgA, bsgB and cobA.     

Karyotaxonomical analysis in the genusAngelica (Umbelliferae)

Morphometric karyotype characters were studied in 25Angelica spp. (Umbelliferae, Apioideae) and in one species of the related genusTommasinia. For three species the chromosome numbers are new. In our study the majority of the species investigated are diploids with 2n = 22, some are tetraploids with 2n = 44 (for these tetraploids also diploid cytotypes are reported in the literature). Among the diploid species,A. miqueliana has a distinct karyotype consisting of submetacentric and acrocentric chromosomes only, the remaining diploids with 2n = 22 as well as tetraploids with 2n = 44 have rather symmetrical karyotypes, consisting of metacentric and submetacentric chromosomes. The very different chromosome number 2n = 28 has been found inA. gmelinii. Its karyotype includes two distinct groups of chromosomes: 8 pairs of rather large metacentrics and submetacentrics and 6 pairs of very short and asymmetrical chromosomes. Chromosome numbers and structures appear to be useful in the taxonomy of some intrageneric taxa inAngelica.     

江豚的染色体核型研究

江豚(Neophocaena phocaenoides)是鲸目(Cetacea)鼠海豚科(Phocaenidae)的一种小型齿鲸,在淡水和海洋中均有分布。关于江豚染色体的研究,国外文献中尚未见记载,国内亦无报道。Pilleri和Gihr(1972,1975)根据江豚的形态解剖学的研究,认为我国产的江豚和印度洋的及日本海的江豚不属同一个种,但国际上对此尚有不同意见。因此,搞清江豚染色体的核型,将可有助于澄清江豚属的的分类问题。本文就我国长江产江豚的染色体核型作初步探讨。     

Cytogenetic analysis of the tamaraw (Bubalus mindorensis): a comparison of R-banded karyotype and chromosomal distribution of centromeric satellite DNAs, telomeric sequence, and 18S-28S rRNA genes with domestic water buffaloes

The karyotype of the tamaraw (Bubalus mindorensis, 2n = 46) was investigated by RBG-banding technique and compared with those of the river and the swamp cytotypes of domestic water buffalo (B. bubalis). The tamaraw karyotype consisted of 6 submetacentric and 16 acrocentric autosome pairs (NAA = 56), and X and Y chromosomes. The RBG-banded karyotype of the three taxa had a high degree of homology, and the tamaraw karyotype could be explained by a Robertsonian translocation between chromosomes 7 and 15 and by a telomere-centromere tandem fusion between chromosomes 4p and 12 of the standardized river buffalo cytotype (2n = 50, NAA = 58). The buffalo satellite I and II DNAs were localized to the centromeric regions of all the tamaraw chromosomes. The biarmed chromosome 2 of the tamaraw resulting from the fusion between chromosomes 7 and 15 of the standard contained much larger amounts of the satellite I DNA than the other biarmed chromosomes, suggesting that this chromosome was formed by a relatively recent Robertsonian fusion. The (TTAGGG)n telomeric sequence was specifically localized to the telomeric region of all the buffalo chromosomes. The 18S + 28S rDNA was localized to the telomeric regions of the chromosomes 5p, 7, 19, 21, and 22 of the tamaraw and of their homologous chromosomes in the river and swamp buffalo cytotypes.     

Chromosome Fragments in DICTYOSTELIUM DISCOIDEUM Obtained from Parasexual Crosses between Strains of Different Genetic Background

The first aneuploid strains of Dictyostelium discoideum have been unambiguously characterized, using cytological and genetic analysis. Three independently isolated, but genetically similar, fragment chromosomes have been observed in segregants from diploids formed between haploid strains derived from the NC4 and V12 isolates of D. discoideum. Once generated, the fragment chromosomes, all of which have V12-derived centromeres, can be maintained in a NC4 genetic background. Genetic evidence is consistent with the view that all three fragment chromosomes studied encompass the region from the centromere to the whiA locus of linkage group II and terminate in the interval between whiA and acrA. From cytological studies, one of the fragment chromosomes consists of approximately half of linkage group II.—We observed no deleterious effect on viability or asexual fruiting-body formation in either haploid or diploid strains carrying an additional incomplete chromosome and hence are disomic or trisomic, respectively, for part of linkage group II. The incomplete chromosome is lost at a frequency of 2 to 3% from disomic and trisomic strains, but surprisingly this loss is not increased in the presence of the haploidizing agent, benlate. A new locus (clyA), whose phenotype is altered colony morphology, is assigned to the region of linkage group II encompassed by the fragment chromosome.     

Genetic analysis of mutations of low (rec) and very high (pop) mitotic-recombination frequency in Aspergillus nidulans.

Summary A mutation (rec) confering low mitotic recombination in a haploid of Aspergillus nidulans carrying the duplication I pab y adE8 bi ⁺/IIdy y ⁺ adE20 bi was tested for its effect on mitotic recombination in diploids and on meiosis. The method involved the building of strains that on mating in pairwise combinations can give heterokaryons and diploids homozygous for different sets of chromosomes coming from the rec strain. Three such diploids were tested so far, in which no effect on recombination frequency was found; it means that if rec affects diploids it is not located on linkage groups III, IV, V, or VII. The strains for building the other diploids have been constructed. The construction of a diploid homozygous for linkage group I from the rec parent required a transfer of the duplicated segment y ⁺ adE20 bi from chromosome II to its original place on chromosome I. A method for this transfer involving two-step selection is described.A mutation (pop) confering very high mitotic-recombination frequency was found to have a profound effect on crossing over in diploids: all the asexual spores show at least one crossing-over event. The high recombination could be due to the effect of pop on chromosome exchange per se, or on chromosome pairing and thus indirectly on exchange. A test designed to support the second hypothesis failed to supply this support. Since there are other results supporting the first hypothesis it is concluded that pop has a direct effect on mitotic crossing over. The possible uses of pop mutants for mitotic genetic mapping, and for testing whether mitotic crossing over is a special case of sister-strand exchange, are discussed.     

Recessive Lethal Mutations and the Maintenance of Duplication-Bearing Strains of Dictyostelium discoideum

Recessive lethal mutations have been isolated and used to maintain n + 1 aneuploid strains of Dictyostelium discoideum carrying a duplication of part or all of linkage group VII. The recessive lethal mutations, relA351 and relB352, arose spontaneously in diploids; no mutagenic treatment was used in the isolation of these mutations. The probable gene order on linkage group VII is: centromere, relB couA, bsgB, cobA, relA. Maintenance of aneuploids disomic for linkage group VII was made possible by complementation of a rel mutation on each linkage group VII homologue by the corresponding wild-type allele on the other linkage group VII homologue. The duplication-bearing disomic strains were slow-growing and produced faster-growing sectors on the colony edge. Haploid sectors probably arise by a combination of mitotic recombination and subsequent loss of one homologue, diploid sectors may be formed by chromosome doubling to 2n + 2, followed by chromosome loss to return to 2n, and aneuploid sectors may arise by deletion or new mutation.     

The karyotype of Nothoscordum arenarium Herter (Gilliesioideae, Alliaceae): A populational and cytomolecular analysis

The genus Nothoscordum Kunth comprises approximately 20 species native to South America. Karyologically, the genus is remarkable for its large chromosomes and Robertsonian translocations. Variation in chromosome number has been recorded in a few polyploid species and it is unknown among diploids. This study presents the chromosome number and morphology of 53 individuals of seven populations of N. arenarium Herter (2n = 10). In addition, karyotype analyses after C-banding, staining with CMA and DAPI, and in situ hybridization with 5S and 45S rDNA probes were performed in six individuals from one population. All individuals exhibited 2n = 10 (6M + 4A), except for one tetraploid (2n = 20, 12M + 8A) and one triploid (2n = 15, 9M + 6A) plant. C-banding revealed the presence of CMA(+) /DAPI (-) heterochromatin in the short arm and in the proximal region of the long arm of all acrocentric chromosomes. The 45S rDNA sites co-localized with the CMA (+) regions of the acrocentrics short arms, while the 5S rDNA probe only hybridized with the subterminal region of a pair of metacentric chromosomes. A change in the pattern of CMA bands and rDNA sites was observed in only one individual bearing a reciprocal translocation involving the long arm of a metacentric and the long arm of an acrocentric chromosome. These data suggest that, despite isolated cases of polyploidy and translocation, the karyotype of N. arenarium is very stable and the karyotypic instability described for other species may be associated with their polyploid condition.     

A new chromosomal race (2n=44) of Nannospalax xanthodon from Turkey (Mammalia: Rodentia)

A new karyotype for blind mole rats was recorded in Tunceli province in Eastern Turkey. The karyotype contained 44 chromosomes, including 13 biarmed pairs, 7 acrocentric pairs, and one heteromorphic pair with a submetacentric and an acrocentric homologue in the autosomal complement (FNa=69). The X chromosome was submetacentric and the Y chromosome medium-sized subtelocentric (FN=73). Distinct dark centromeric C-bands were observed on most of the biarmed and three pairs of the acrocentric autosomes. The NORs were detected on short arms of three subtelocentric pairs and one acrocentric pair of autosomes. The diploid number of chromosomes and the karyotype characteristics observed are obviously unique among hitherto studied populations of blind mole rats and the complement can be evaluated as a new chromosome race of Nannospalax xanthodon. The distribution ranges of individual chromosome races of the species recorded in Eastern Anatolia are revised and possible interracial hybridization is discussed in respect of the finding of a new race.     

Karyotype of the Snow Sculpin <Emphasis Type="Italic">Myoxocephalus brandti</Emphasis> Steindachner (Cottidae) from Peter the Great Bay,Sea of Japan

The karyotype of the snow sculpin Myoxocephalus brandti, 2n = 44, NF = 46, from Peter the Great Bay was studied. Two-armed chromosomes were presented by one pair of metacentric chromosomes of medium size; one-armed chromosomes included two pairs of large subtelocentric chromosomes and a pair of large acrocentric chromosomes. Ag-NOR-staining in the telomere vicinity revealed nucleolus-organizing regions in one metacentric chromosome and in one medium size acrocentric chromosome in one of the fishes, in two homological small acrocentric chromosomes in three fishes, and in one acrocentric chromosome of average size in six fishes. No difference between the male and female karyotypes and any type of variability was revealed. The karyotypes of the snow sculpin M. brandti and the frog sculpin M. stelleri were compared. Their distinctions and similarities were displayed.Original Russian Text Copyright ¢ 2005 by Biologiya Morya, Ryazanova.     

Chromosome evolution involving Robertsonian rearrangements in Xyrichthys fish (Labridae, Perciformes)

Three Xyrichthys fish (Labridae, Perciformes), X. pavo, X. dea, and X. twistii, were cytogenetically studied. X. pavo and X. dea had 2n = 44 chromosomes, which were all acrocentric. X. twistii had 2n = 22 chromosomes consisting of eighteen meta- and submetacentric and four acrocentric chromosomes. The cellular DNA contents of X. pavo and X. twistii measured using flow cytometry were nearly equal. These results suggest that the karyotype of X. twistii evolved by decreasing the number of chromosomes by fusion events, probably Robertsonian fusion. Cytogenetic relationships among the three species were surmized on the basis of features on the karyotypes and the NOR locations. A large gap in the chromosome number between 2n = 44 and 2n = 22 is an interesting feature related to the process of chromosome evolution.     

A Genetic Map of DICTYOSTELIUM DISCOIDEUM Based on Mitotic Recombination

A genetic map of the cellular slime mold Dictyostelium discoideum is presented in which 42 loci are ordered on five of the seven linkage groups. Although most of the loci were ordered using standing mitotic crossing-over techniques in which recessive selective markers were employed, use was also made of unselected recombined haploid strains. Consistent with cytological studies in which the chromosomes appear to be acrocentric, only a single arm has been found for each of the five linkage groups studied. The mating-type locus, matA, has been located in the tsgE-sprA interval on linkage group I on the basis of studies on diploids formed between strains of opposite mating type that have escaped from vegetative incompatibility.     

Contributions to the cytotaxonomy of the Commelinaceae. Chromosome evolution in Tradescantia section Cymbispatha

The five species of Tradescantia section Cymbispatha studied, including one species T. poelliae D. R. Hunt, have chromosome numbers of In = 12, 14, 16, 22, 28, 30 and 36 and karyotypes of acrocentric, metacentric or telocentric chromosomes, or mixtures of both acrocentric and metacentric chromosomes. The numbers of major chromosome arms of these cytotypes give a nombre fondamentaP series of 14, 28, 42 and 56 which, in combination with meiotic analyses, indicates plants which, in genetical terms at least, are diploid, tetraploid, hexaploid and octoploid. This series has evolved from a 2 n = 14 acrocentric or telocentric karyotype by a combination of Robertsonian fusion and polyploidy. Pseudo-iso-chromosomes are sometimes formed in this evolutionary development and can persist as stable members of normal complements.     

Contributions to the cytotaxonomy of the Commelinaceae. Chromosome evolution in Tradescantia section Cymbispatha

The five species of Tradescantia section Cymbispatha studied, including one species T. poelliae D. R. Hunt, have chromosome numbers of In = 12, 14, 16, 22, 28, 30 and 36 and karyotypes of acrocentric, metacentric or telocentric chromosomes, or mixtures of both acrocentric and metacentric chromosomes. The numbers of major chromosome arms of these cytotypes give a nombre fondamentaP series of 14, 28, 42 and 56 which, in combination with meiotic analyses, indicates plants which, in genetical terms at least, are diploid, tetraploid, hexaploid and octoploid. This series has evolved from a 2 n = 14 acrocentric or telocentric karyotype by a combination of Robertsonian fusion and polyploidy. Pseudo-iso-chromosomes are sometimes formed in this evolutionary development and can persist as stable members of normal complements.     

The complete karyotype of Aspergilius niger: the use of introduced electrophoretic mobility variation of chromosomes for gene assignment studies

A method is described for unambiguous assignment of cloned genes to Aspergillus niger chromosomes by CHEF gel electrophoresis and Southern analysis. All of the eight linkage groups (LGs), with the exception of LG VII, have previously been assigned to specific chromosomal bands in the electrophoretic karyotype of A. niger. Using a LG VII-specific probe (nicB gene of A. niger) we have shown that LG VII corresponds to a chromosome of about 4.1 Mb. Furthermore, genetic localization of three unassigned genes (glaA, agIA and pepA) in strains in which these genes had been replaced by a selectable marker gene led to a revised karyotype for the chromosomes corresponding to LGs VIII and VI. The revised electrophoretic karyotype reveals only 5 distinct bands. The presence of three pairs of equally sized chromosomes precluded assignment of genes to one specific chromosome in the wild-type strain. However, unambiguous chromosome assignment of cloned genes using CHEF-Southern analysis was demonstrated using a set of A. niger strains with introduced chromosomal size variation. The availability of these tester strains obviates the need to isolate or construct mutant. strains for the purpose of chromosome assignment.     

Defining the orientation of the tandem fusions that occurred during the evolution of Indian muntjac chromosomes by BAC mapping

The Indian muntjac (Muntiacus muntjak vaginalis) has a karyotype of 2n=6 in the female and 7 in the male, the karyotypic evolution of which through extensive tandem fusions and several centric fusions has been well-documented by recent molecular cytogenetic studies. In an attempt to define the fusion orientations of conserved chromosomal segments and the molecular mechanisms underlying the tandem fusions, we have constructed a highly redundant (more than six times of whole genome coverage) bacterial artificial chromosome (BAC) library of Indian muntjac. The BAC library contains 124,800 clones with no chromosome bias and has an average insert DNA size of 120 kb. A total of 223 clones have been mapped by fluorescent in situ hybridization onto the chromosomes of both Indian muntjac and Chinese muntjac and a high-resolution comparative map has been established. Our mapping results demonstrate that all tandem fusions that occurred during the evolution of Indian muntjac karyotype from the acrocentric 2n=70 hypothetical ancestral karyotype are centromere–telomere (head–tail) fusions.     

Different rate of intrapopulation chromosome polymorphism in two species of Black Sea Blennies (Blenniidae,Pisces)

Somatic karyotypes in seven specimens of Blennius sanguinolentus include 22 subtelocentric and 26 acrocentric chromosomes, whereas one male has 2n=47=1M+22ST+24A: polymorphism is evidently a result of centric fusion of two acrocentrics. Blennius tentacularis is characterized by the availability of four karyomorphs out of which three coincide with karyotypes described earlier (Carbone et al., 1987). Karyttype-I consists of a 48 small uni-armed chromosome, but both karyotypes II and III with 2n=48 and 2n=47 respectively include one large acrocentric chromosome, and karyotype-IV has one large submetacentric out of the 47 chromosomes. Karyotypic variability of B. tentacularis is attributed either to polymorphism by 1–3 chromosome rearrangements or to availability of sex-determining mechanism, including the Y-autosome translocation. This diverse series of male karyomorphs may reflect the complicated behavioural structure.     

Karyotype analysis of mithun (Bos frontalis) and mithun bull x Brahman cow hybrids

We examined the cytogenetics of mithun (Bos frontalis), a domesticated version of the Asian gaur, and hybrids (F(1) generation) produced by artificial insemination of Brahman cows (Bos indicus) with mithun semen. Reproductive potential was also examined in the F(1) generation and a backcrossed heifer for utilization of heterosis. Metaphase chromosome spreads were examined by conventional staining and fluorescence in situ hybridization hybridized with the entire chromosome 1 of mithun as a specific probe. Chromosome 1 of mithun was found to be equivalent to Bos taurus chromosomes 2 and 28. The karyotype of the female mithun (N = 4) comprised 58 chromosomes, including 54 acrocentric and four large submetacentric chromosomes, without the four acrocentric chromosomes found in the domesticated species B. indicus. However, one of the four female mithuns with a normal mithun phenotype had an abnormal karyotype (2n = 59), indicating introgression from B. taurus or B. indicus. The F(1) karyotypes (N = 6, 3♂3♀) of the mithun bull × Brahman cow cross had 2n = 59, intermediate between their parents; they were consistent heterozygous carriers with a centric fusion involving rob(2;28), as expected. Two pronounced red signals were seen in the mithun karyotypes, three red signals in the mithun × Brahman hybrids, and four red signals in the Brahman cattle, in good agreement with centric fusion of bovine rob(2;28). The female backcross hybrid (N = 1) with 2n = 59 had a similar chromosome configuration to the F(1) karyotypes and had rob(2;28). Such female backcross hybrids normally reproduce; however, the F(1) bulls (N = 3) had not yet generated normal sperm at 24 months.     

Investigation of the het genes that control heterokaryon incompatibility between members of heterokaryon-compatibility (h-c) groups A and G1 of Aspergillus nidulans

A chromosome assay method was used to determine the heterokaryon compatibility relationships between strains belonging to heterokaryon-compatibility (h-c) groups A and G1 of Aspergillus nidulans. A hybrid strain (RD15) was isolated following protoplast fusion of strains 65-5 (h-cA) and 7-141 (h-cG1). The morphology of RD15 was severely abnormal compared to diploid strains of A. nidulans produced from heterokaryon-compatible haploid parents. Inocula of RD15 were induced to haploidize on medium containing Benlate and a parasexual progeny sample of 291 haploid segregants was obtained. The progeny strains were genotyped for standard markers. Allelic ratios and pairwise marker segregations were determined. Pairs of progeny strains that carried different alleles for the standard markers on each linkage group in turn were tested for compatibility. Strain pairs that possessed different alleles for the markers on linkage groups II, III, V, VI and VII were incompatible indicating the presence of heterokaryon-incompatible (het) genes on these linkage groups. Backcrosses to an h-cGl strain showed that two het genes were located on linkage group III and confirmed a total of six het gene differences between the h-cA and h-cGl strains.