Nonrandom chromosome arrangements in germ line nuclei of Sciara coprophila males: the basis for nonrandom chromosome segregation on the meiosis I spindle

Meiosis I in males of the Dipteran Sciara coprophila results in the nonrandom distribution of maternally and paternally derived chromosome sets to the two division products. Based on an earlier study (Kubai, D.F. 1982. J. Cell Biol. 93:655-669), I suggested that the meiosis I spindle does not play a direct role in the nonrandom sorting of chromosomes but that, instead, haploid sets are already separated in prophase nuclei well before the onset of spindle formation. Here I report more direct evidence that this hypothesis is true; this evidence was gained from ultrastructural reconstruction analyses of the arrangement of chromosomes in germ line nuclei (prophase nuclei in spermatogonia and spermatocytes) of males heterozygous for an X- autosome chromosome translocation. Because of this translocation, the maternal and paternal chromosome sets are distinguishable, so it is possible to demonstrate that (a) the two haploid chromosome sets occupy distinct maternal and paternal nuclear compartments and that (b) nuclei are oriented so that the two haploid chromosome sets have consistent relationships to a well-defined cellular axis. The consequences of such nonrandom aspects of nuclear structure for chromosome behavior on premeiotic and meiotic spindles are discussed.     

Association mapping of<Emphasis Type="Italic"> Stagonospora nodorum</Emphasis> blotch resistance in modern European winter wheat varieties

Association mapping in populations relevant for wheat breeding has a large potential for validating and fine-mapping QTLs identified in F2- or DH (double haploid)-derived populations. In this study, associations between markers in the region of QSng.sfr-3BS, a major QTL for resistance to Stagonospora nodorum glume blotch (SNG), and SNG resistance were investigated by linkage and association analyses. After increasing marker density in 240 F_5:7 recombinant inbred lines (RILs), QSng.sfr-3BS explained 43% of the genetic variance and peaked 0.6 cM proximal from the marker SUN2-3B. Association between SNG resistance and markers mapped in the region of QSng.sfr-3BS was investigated in a population of 44 modern European winter wheat varieties. Two genetically distinct subpopulations were identified within these lines. In agreement with linkage analyses, association mapping by a least squares general linear model (GLM) at marker loci in the region of QSng.sfr-3BS revealed the highest association with SNG resistance for SUN2-3B (p < 0.05). Association mapping can provide an effective mean of relating genotypes to complex quantitative phenotypes in hexaploid wheat. Linkage disequilibrium (r ²) in chromosome 3B extended less than 0.5 cM in 44 varieties, while it extended about 30 cM in 240 RILs, based on 91 SSR and STS marker-pair comparisons. This indicated that the association mapping population had a marker resolution potential at least 390-fold higher compared to the RIL population. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Meiosis in polyhaploid Hordeum: hemizygous ineffective control of diploid-like behaviour in a hexaploid?

Meiotic chromosome behaviour was studied in the hexaploid Hordeum parodii (2n=6x=42) and in six haploids (2n=3x=21) obtained from a cross between H. parodii and H. bulbosum (2n=2x=14) whereby all bulbosum chromosomes were selectively eliminated. The alloploid nature of H. parodii was evident from the exclusive bivalent formation at the hexaploid level and the low and variable number of bivalents in its haploid derivatives. In haploids, both nonhomologous (intragenomic) and homoeologous (intergenomic) chromosomes paired at prophase. Foldbacks in single chromosomes, bivalents and trivalents were observed at prophase and metaphase I. At diakinesis, the associations involved a maximum of 20 chromosomes which decreased to 12 by metaphase I. This decrease was attributed to the failure of the non-homologous associations to persist until metaphase I. A hemizygous-ineffective control for the diploid-like behaviour of the hexaploid parodii is proposed to explain the homeologous chromosome pairing in its haploid derivatives.     

The parthenogenetic Marmorkrebs (Malacostraca: Decapoda: Cambaridae) is a triploid organism

There is a close association between parthenogenesis and polyploidy. For this reason, we undertook a karyological analysis to test whether the parthenogenetic Marmorkrebs, Procambarus fallax forma virginalis, possesses an enlarged set of chromosomes. For this purpose, we karyotyped the Marmorkrebs, the sexual form of P. fallax (together called P. fallax complex), and the closely related species P. alleni. The latter shows 94 chromosomes in the haploid condition. In contrast to this, we found a haploid set of 92 chromosomes in individuals of the P. fallax complex. However, in mitotic metaphases the sexual form shows 184 chromosomes, whereas the Marmorkrebs possesses 276 chromosomes. Hence, the parthenogenetic Marmorkrebs reveals a triple amount of the haploid chromosome number. In addition, we detected a strikingly large subtelocentric chromosome which appears once in haploid and twice in diploid cells of sexual individuals of the P. fallax complex. In the parthenogenetic Marmorkrebs, this prominent chromosome occurs thrice. All this clearly reveals that the Marmorkrebs is a triploid organism. The applicability of the used methods, the significance of polyploidy in evolution of Decapoda, putative pathways to parthenogenetic triploidy, a possible hybrid origin and the scientific and ecological consequences of an increased chromosome set in Marmorkrebs are discussed.     

Structural karyotypic variability and polyploidy in natural populations of the South American <Emphasis Type="Italic">Lathyrus nervosus</Emphasis> Lam. (Fabaceae)

Knowledge of the chromosome variation in wild populations is essential to understand the pathways and restrictions of karyotype evolution in plants. The aim of this study is to conduct an intraspecific analysis of the karyotypes by fluorochrome banding and ribosomal DNA (rDNA) loci detection by fluorescent in situ hybridization (FISH) and of the meiotic behaviour in natural populations of Lathyrus nervosus, sect. Notolathyrus. Chromosome banding showed that, despite the high constancy in the karyotype formula and in the rDNA loci among populations, there is intraspecific variation in the amount and distribution pattern of 4’,6-diamidino-2-phenylindole (DAPI⁺) heterochromatin. However, those changes were not related to the total chromosome length of the haploid complements. This fact demonstrates that structural chromosome changes may be one of the most important mechanisms for karyotype variation among natural populations of L. nervosus. The chromosome number surveyed at the population level revealed the first case of polyploidy in South American species and the first case of uneven polyploidy of the genus. All the chromosome markers analysed indicated that the polyploids found originated by autopolyploidy. The meiotic analysis showed different chromosome abnormalities that may be generating numerical and structural changes in the sporads. The finding of unreduced gametes that are alive at anthesis suggests sexual polyploidization as the most probable mechanism involved in the origin of these 3x and 4x autopolyploid cytotypes in L. nervosus.     

A telocentric translocation responsible for variegation in Petunia

Striped mutants of Petunia were isolated after -ray treatment of zygotes and from the progeny of a haploid plant. This striped phenotype appeared to be associated with a telocentric translocation in which one arm of chromosome I was transferred to the end of the long arm of chromosome II.The phenotype and the breeding behaviour of the striped plants are explained on the basis of a mechanism similar to the breakage-fusion-bridge cycle described earlier in maize endosperm.The translocation is marked by the dominant allele P₁ responsible for the synthesis of petunidin in flowers. The locus of this gene is on chromosome I.There is evidence for non-homologous pairing at meiosis of a haploid plant of Petunia hybrida.     

Mapping of a novel QTL for resistance to cereal cyst nematode in wheat

Cereal cyst nematode (CCN; Heterodera avenae Woll.) is a root pathogen of cereals that can cause severe yield losses in intolerant wheat cultivars. Loci for resistance to CCN, measured by a seedling bioassay, were identified by creating a genetic map based on a Trident/Molineux doubled haploid population of 182 lines. A novel locus accounting for up to 14% of the resistance to CCN was mapped to chromosome 1B of Molineux by association with microsatellite marker loci Xwmc719 and Xgwm140. This locus acts additively with the previously identified CCN resistance loci identified on chromosomes 6B (Cre8) and 2A (Cre5 on the VPM1 segment) in this population to explain 44% of the genetic variance for this major wheat pathogen.     

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.     

<Emphasis Type="Italic">In vitro</Emphasis> studies to produce double haploid in <Emphasis Type="Italic">Indica</Emphasis> hybrid rice

The aim of this investigation was to improve in vitro the technique of production of double haploid in Indica hybrid rice by combining anther culture, hormone shock and doubling chromosome. It was discussed how to avoid somaclonal variation during culturing and to reduce the time of this process. The anthers of KDML 105 × SPR 1 (Indica × Indica) were cultured in Linsmaier and Skoog (LS) medium, which contained nutrients, growth regulators [(2,4,-dichlorophenoxy acetic acid (2,4-D) and naphthalene acetic acid (NAA)] and organic compounds, and then subcultured by inducing embryo-like structure (ELS) LS media. During 4 weeks used LS media supplemented with 10 μM KNO³ + 2 mg/L 2,4-D + 2 mg/L NAA + 20% coconut water + 1 mg/L of activated charcoal had induced high embryogenic frequent callus with length of 4–5 mm. The supplementation of 0.2 g/L colchicine and 100 μM 2,4-D was the most efficient in LS media. Over 70% of viable double haploid ELS were produced in 8 weeks and subcultured only twice compared with conventional anther which takes more than 12 weeks. This new technique can therefore be applied to rice in order in shorten time to produce higher number of double haploid plantlets.     

Mitotic Chromosome Loss in a Disomic Haploid of SACCHAROMYCES CEREVISIAE

Experiments designed to characterize the incidence of mitotic chromosome loss in a yeast disomic haploid were performed. The selective methods employed utilize the non-mating property of strains disomic for linkage group III and heterozygous at the mating type locus. The principal findings are: (1) The frequency of spontaneous chromosome loss in the disome is of the order 10^-4 per cell; this value approximates the frequency in the same population of spontaneous mitotic exchange resulting in homozygosity at the mating type locus. (2) The recovered diploids are pure clones, and thus represent unique events in the disomic haploid. (3) Of the euploid chromosomes recovered after events leading to chromosome loss, approximately 90% retain the parental marker configuration expected from segregation alone; however, the remainder are recombinant for marker genes, and are the result of mitotic exchanges in the disome, especially in regions near the centromere. The recombinant proportion significantly exceeds that expected if chromosome loss and mitotic exchange in the disome were independent events. The data are consistent with a model proposing mitotic nondisjunction as the event responsible for chromosome loss in the disomic haploid.     

Nonrandom Representation of Sex-Biased Genes on Chicken Z Chromosome

Several lines of evidence suggest that the X chromosome of various animal species has an unusual complement of genes with sex-biased or sex-specific expression. However, the study of the X chromosome gene content in different organisms provided conflicting results. The most striking contrast concerns the male-biased genes, which were reported to be almost depleted from the X chromosome in Drosophila but overrepresented on the X chromosome in mammals. To elucidate the reason for these discrepancies, we analysed the gene content of the Z chromosome in chicken. Our analysis of the publicly available expressed sequence tags (EST) data and genome draft sequence revealed a significant underrepresentation of ovary-specific genes on the chicken Z chromosome. For the brain-expressed genes, we found a significant enrichment of male-biased genes but an indication of underrepresentation of female-biased genes on the Z chromosome. This is the first report on the nonrandom gene content in a homogametic sex chromosome of a species with heterogametic female individuals. Further comparison of gene contents of the independently evolved X and Z sex chromosomes may offer new insight into the evolutionary processes leading to the nonrandom genomic distribution of sex-biased and sex-specific genes. Electronic Supplementary Material Electronic Supplementary material is available for this article at and accessible for authorised users. [Reviewing Editor: Dr. Manyuan Long]     

Molecular characterization and genetic mapping of class I and class II MHC genes of the domestic cat

The major histocompatibility complex (MHC) of the domestic cat has been poorly characterized to date, primarily because of numerous difficulties in the preparation of allotypic sera. We present here a comparative analysis of class I and class II genes in domestic cat populations using molecular probes of the MHC from man and mouse. The cat possesses a minimum of 20 class I loci and 5 class II genes per haploid genome. Class I genes of the domestic cat expressed limited restriction fragment length polymorphism. The average percent difference of the size of DNA fragments between individual cats was 9.0 %, a value five times lower than the value for mice, but comparable to the human DNA polymorphism level. Class I and class II genes were both genetically mapped to feline chromosome B2 using a panel of rodent x cat somatic cell hybrids. Since feline chromosome B2 is syntenically homologous to human chromosome 6 and mouse chromosome 17, these results affirm the linkage conservation of the MHC-containing linkage group in the three mammalian orders.     

Nuclear conditions in haploid Pelargonium in vivo and in vitro

In the shoot apices of the haploid Pelargonium cultivar Kleine Liebling, all mitoses are haploid (n = 9); however, ca. 20% of the interphase nuclei have DNA contents greater than 2C (up to 4C), indicating a tendency to chromosome endoreduplication in this material. — In internodes in vivo, the few mitoses present are haploid (quite probably, cambium cells); in addition to haploid interphases (1C to 2C DNA contents), endoreduplicated (endopolyploid) nuclei and nuclei in the course of endoreduplication occur with a frequency of ca. 40–50% (DNA contents up to 8C). — When internodes are cultured in vitro, differentiated cells are stimulated to divide, thus forming a population of diploid and tetraploid mitoses in addition to the preexistent meristem (haploid) cell population. In the process of time, diploid and tetraploid mitoses continue to be present in the callus, whilst haploid mitoses may decrease in number and eventually disappear. All mitoses analyzed had euploid chromosome numbers (9, 18 and 36) and their DNA contents were correspondingly 2C, 4C and 8C. Since no extensive chromosome counts were made, aneuploidy in the cultured material cannot be excluded; but, if occurring, it should be rather rare. — Under the experimental conditions used, prolonged culture in vitro leads to the production of nuclei with DNA contents (16C and 32C) greater than those occurring in vivo (8C), due to one and two additional DNA replications respectively beyond the limits attained in vivo. Even in these cultures, however, a population of the meristematic haploid cell line (DNA values 1C to 2C) is still present. — The present results are discussed in their relations with previous works on nuclear conditions in vivo and in vitro and on regeneration processes in cultured tissues in plants.     

Association between vitamin D receptor gene polymorphisms and bone mineral density in Chinese women

Vitamin D receptor (VDR) is implicated in the regulation of bone mineral density (BMD). In this study, we performed a meta-analysis to evaluate the association between the VDR BsmI (rs1544410) and ApaI (rs7975232) polymorphisms and BMD in Chinese women. Literature was retrieved from PubMed and other databases. The studies on the association between VDR BsmI and ApaI genotypes and BMD at the lumbar spine, the femoral neck, the trochanter or the Ward’s triangle in Han Chinese women were included in this meta-analysis. Pooled BMD differences and 95% confidence intervals (CIs) were calculated using random- or fixed- effects model. Twenty-five eligible studies, which included 4,075 Chinese women, were identified. No significant difference was observed for either genotype when the meta-analysis was limited to premenopausal women. In postmenopausal women, BMD differences were significant for BB vs. Bb [−0.029 (95% CI −0.056, −0.002) g/m², P = 0.037] at the femoral neck, AA vs. Aa [−0.029 (95% CI −0.051, −0.006) g/m², P = 0.012] at the lumbar spine, and Aa vs. aa [0.022(95% CI 0.011, 0.033) g/m², P = 0.000] at the trochanter. These results suggest a modest but statistically significant association between VDR BsmI and ApaI polymorphisms and BMD in Chinese postmenopausal women, with higher BMD in heterozygous subjects. More epidemiological and mechanistic studies are needed to further investigate the role of VDR gene polymorphisms in regulating BMD and osteoporosis in the future.     

Construction of a YAC library from a Beta vulgaris fragment addition and isolation of a major satellite DNA cluster linked to the beet cyst nematode resistance locus Hs1 pat−1

A YAC library was constructed from the Beta vulgaris fragment addition AN5-203b. This monosomic fragment addition harbors an approximate 12-Mbp fragment of B.patellaris chromosome 1 accomodating the Hs1 ^pat-1 conferring resistance to the beet cyst nematode (Heterodera schachtii). The YAC library consists of 20,000 YAC clones having an average size of 140 kb. Screening with organelle-specific probes showed that 12% of the clones contain chloroplast DNA while only 0.2% of the clones hybridizes with a mitochondrial specific probe. On the basis of a sugar beet haploid genome size of 750 Mbp this library represents 3.3 haploid genome equivalents. The addition fragment present in AN5-203b harbors a major satellite DNA cluster that is tightly linked to the Hs1 ^pat-1 locus. The cluster is located on a single 250-kb EcoRI restriction fragment and consists of an estimated 700–800 copies of a 159-bp core sequence, most of which are arranged in tandem. Using this core sequence as a probe, we were able to isolate 1 YAC clone from the library that contains the entire 250-kb satellite DNA cluster.Abbreviations YAC Yeast artificial chromosome - BCN beet cyst nematode - RAPD random amplified polymorphic DNA - RFLP restriction fragment length polymorphism     

Cytological studies on F1 hybrids of Solanum integrifolium with S. melongena and S. melongena var. insanum

S. integrifolium (2n = 24) can easily be crossed as the pistillate parent with S. melongena (2n = 24) and S. melongena var. insanum (2n = 24). However, crosses in the other direction do not succeed. Both hybrids are vigorous. Chromosome association at diakinesis and metaphase I was studied. Chromosome associations higher than bivalents were observed in the hybrids indicating structural repatterning of chromosomes. The modal chromosome association in hybrids was twelve bivalents per PMC. This is suggestive of the retention of ancestral chromosome homeologies by the taxa concerned. Despite regular meiosis both hybrids were highly pollen-sterile (about 95%), which was attributed to segregational events of the recombined chromosomes.     

A chromosome study ofCharaxes jasius L. (Lepidoptera,Nymphalidae)

The haploid chromosome complement ofCharaxes jasius is n=25 in both males and females. The chromosomes in the mitotic metaphase are rod⁻ and dot-shaped; the primary constriction, even after treatment with hypotonic solution, is lacking in them. Meiosis in females is achiasmatic. This research was supported by a grant from M.P.I. 40%-1984.     

Abdominal Visceral Fat is Associated with a BclI Restriction Fragment Length Polymorphism at the Glucocorticoid Receptor Gene Locus

Several investigations have suggested that body fat distribution is influenced by nonpathologic variations in the responsiveness to Cortisol. Genetic variations in the glucocorticoid receptor (GRL) could therefore potentially have an impact on the level of abdominal fat. A restriction fragment length polymorphism (RFLP) has previously been detected with the BelI restriction enzyme in the GRL gene identifying two alleles with fragment lengths of 4.5 and 2.3 kb. This study investigates whether abdominal fat areas measured by computerized tomography (CT) are associated with this polymorphism in 152 middle-aged men and women. The less frequent 4.5-kb allele was found to be associated with a higher abdominal visceral fat (A VF) area independently of total body fat mass (4.5/4.5 vs. 2.3/2.3 kb genotype; men: 190.7 ± 30.1 vs. 150.7 ± 33.3 cm², p=0.04; women: 132.7 ± 37.3 vs. 101.3 ± 34.5 cm², p=0.06). However, the association with AVF was seen only in subjects of the lower tertile of the percent body fat level. In these subjects, the polymorphism was found to account for 41% (p=0.003) and 35% (p=0.007), in men and women, respectively, of the total variance in AVF area. The consistent association between the GRL polymorphism detected with BelI and AVF area suggests that this gene or a locus in linkage disequilibrium with the BelI restriction site may contribute to the accumulation of AVF.     

Quantitative analysis of diploid translocation heterozygotes: test of models and equations

Summary Equations have been derived for two different models of chromosome pairing and chiasmata distribution. The first model represents the normal condition and assumes complete synapsis of homologous bivalents and the arms of interchange quadrivalents. This is followed by a nonrandom distribution of chiasmata among bivalents and multivalents such that each bivalent or bivalent-equivalent always has at least one chiasma. Univalents occur only as part of a III, I configuration at diakinesis or metaphase I. The second model assumes that a hologenomic mutation is present in which all chromosomes of a genome are equally affected. Two different assumptions can be made for such a mutation, and both give the same results: (1) homologous or homoeologous chromosome arms may be randomly paired or unpaired, but synapsis always leads to a crossover; (2) homologous or homoeologous arms always pair, but chiasmata are randomly distributed among the arms. The meiotic configurations at diakinesis or metaphase I are the same for both assumptions. Meiotic configurations of normal diploid interchange heterozygotes show good agreement with numbers predicted by the equations for nonrandom chiasmata distribution among configurations. Inter-specific hybrids with supernumerary chromosomes produced meiotic configurations frequencies in agreement with predictions of equations for random chiasmata distribution, but a hybrid without supernumeraries fitted the nonrandom expectations.     

The genomic relationship between Glycine max (L.) Merr. and G. soja Sieb. and Zucc. as revealed by pachytene chromosome analysis

Summary This study was conducted with the objective of determining the genomic relationship between cultivated soybean (Glycine max) and wild soybean (G. soja) of the subgenus Soja, genus Glycine. Observations on cross-ability rate, hybrid viability, meiotic chromosome pairing, and pollen fertility in F ₁ hybrids of G. max × G. soja and reciprocals elucidated that both species hybridized readily and set mature putative hybrid pods, generated vigorous F₁ plants, had a majority of sporocytes that showed 18II + 1IV chromosome association at diakinesis and metaphase I, and had a pollen fertility that ranged from 49.2% to 53.3%. A quadrivalent was often associated with the nucleolus, suggesting that one of the chromosomes involved in the interchange is a satellited chromosome. Thus, G. max and G. soja genetic stocks used in this study have been differentiated by a reciprocal translocation. Pachytene analysis of F₁ hybrids helped construct chromosome maps based on chromosome length and euchromatin and heterochromatin distribution. Chromosomes were numbered in descending order of 1–20. Pachytene chromosomes in soybean showed heterochromatin distribution on either side of the centromeres. Pachytene analysis revealed small structural differences for chromosomes 6 and 11 which were not detected at diakinesis and metaphase I. This study suggests that G. max and G. soja carry similar genomes and validates the previously assigned genome symbol GG.Research supported in part by the Illinois Agricultural Experiment Station and U.S. Department of Agriculture Competitive Research Grant (85-CRCR-1-1616)