摘要:

The objectives of this study were to map and tag the previously undescribed eyespot resistance genePchDvon chromosome 4V ofDasypyrum villosumin a wheat background. The 82 F2plants used for mapping were produced from a cross between a susceptible\i wheat 'Yangmai-5' (4V(4D)) substitution line and a resistant wheat 'Chinese Spring' disomic addition line of chromosome 4V ofD. villosum. Segregation for resistance and susceptibility among F2plants was 3:1, indicating that resistance was controlled by a single dominant gene.PchDvmapped to the distal part of chromosome 4V and was bracketed by two RFLP markers,Xcdo949andXbcd588, in a 33-cM interval. This distance could not be reduced, owing to a lack of polymorphic loci in this region. Theoretically, double recombination in this region occurs in 3.3% of the individuals; therefore, 96.7% of the selected genotypes would havePchDv, with simultaneous selection for both flanking markers. Double recombination between the flanking markers was observed in 2 out of 82 (2.4%) F2individuals.

ISSN:0831-2796    

DOI:10.1139/g97-092

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The imaginal discs ofDrosophilaare a useful experimental system in which we can study the origin and genetic determination of spatial patterns in development. This involves the separation of the disc-cell population into distinct lineage compartments, based on clonally transmitted expression states of a number of known selector genes. However, these commitments can be abrogated and the compartment boundaries redeployed, when repatterning occurs in cultured disc fragments. This has so far only been explained using the idea of positional information. The genetic basis of this property of the imaginal disc system and its relationship to compartments have not been identified. Here we have screened over 470 recessive lethal P-lacZenhancer-trap insertions from the Berkeley Drosophila Genome Project for expression after cell death, which initiates pattern respecification in the imaginal discs. The positive lines obtained identify essential genes that may be important for pattern formation. Most show patterned imaginal disc expression, and many have maternal or zygotic effects on embryonic development. One is an allele ofschnurri, a gene that encodes a component of thedecapentaplegic(dpp)signal transduction pathway used for positional signalling in the embryo and in imaginal discs.

ISSN:0831-2796    

DOI:10.1139/g97-099

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The endemic New Zealand frogLeiopelma hochstetterihas variable numbers of mitotically stable B chromosomes. To assess whether the B chromosomes were derived from the autosome complement, they were isolated by micromanipulation and their DNA amplified by degenerate oligonucleotide primed PCR. Southern hybridizations of B chromosome DNA probes to genomic DNA from males and females characterized by differing numbers of B chromosomes demonstrated that the B chromosomes were derived from the univalent W sex chromosome characteristic of North Island populations. The presence of homologous B chromosome specific sequences from geographically distinct populations indicates a single origin of the B chromosomes. Furthermore, a primitive homology shared by B chromosomes and the W sex chromosome from an ancestral WZ/ZZ karyotype, which is still present in frogs from Great Barrier Island, shows that the B chromosomes originated soon after the univalent W sex chromosome had originated. Sequence analysis revealed that B chromosome DNA is composed of repeat sequences and has the potential to form stable hairpin structures. The molecular dynamics of these structures may reflect an inherent propensity to undergo rapid change in nucleotide sequence and chromosome structure.

ISSN:0831-2796    

DOI:10.1139/g97-091

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

TheDc8gene of carrot (Daucus carotaL.) shows differential expression during embryo development. Changes in methylation patterns of a segment of about 500 bp (from base + 120 to base -446) ofDc8allele 6 were investigated by treating genomic DNA, extracted from embryogenic callus at different stages of development, with sodium bisulfite to modify nonmethylated cytosines. Following asymmetric (strand-specific) amplification, base sequences for samples from each developmental stage were determined for each strand directly from the PCR products or from cloned PCR products. Different methylation patterns were detected in the two strands. The 5' to 3' sense (coding) strand was almost completely nonmethylated, whereas almost all the cytosines in the 3' to 5' (template) strand were methylated. By 71 days after transfer to embryo-inducing medium, few methylcytosines remained; those that were present were generally near the TATA box or in a region beyond -300. The cytosines that were methylated were not limited to CG or CNG sequences. The difference in the extent of methylation between the two complementary strands implies either that there is a mechanism for strand-specific methylation, or that complementary sequences can differ greatly in sensitivity to bisulfite treatment or PCR amplification.

ISSN:0831-2796    

DOI:10.1139/g97-100

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

We have cloned and characterized two highly reiterated, tandemly repeated, and A + T richMboI DNA fragments, one inCirrhina mrigala(Cyprinidae), with a monomer size of 266 bp, and one inClarias batrachus(Clariidae), with a monomer size of 227 bp. TheMboI fragment inC. mrigalais species-specific and absent in other carps, such asCatla catlaandLabeo rohita. TheMboI fragment inC. batrachuswas also present in two other catfishes tested, namelyClarias gariepinusandHeteropneustes fossilis. InC. mrigalaxC. catlaandC. mrigalaxL. rohitahybrids, theC. mrigalaspecificMboI fragment is inherited uniparentally. In the reciprocal hybrids ofC. batrachusxH. fossilis,the satellite ladder contains the bands of both parental species. TheMboI satellite of carp may be useful in genetic introgression analysis and that of catfish in distinguishing between gynogenetic progeny and true hybrids.

ISSN:0831-2796    

DOI:10.1139/g97-096

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The wild nightshadeSolanum lycopersicoidespossesses a number of disease- and arthropod-resistance and environmental stress tolerance traits of potential value for the cultivated tomato,Lycopersicon esculentum. F1hybrids are readily obtained by sexual crosses, but backcrosses to tomato are hindered by sterility and incompatibility barriers. In the present studies, intergeneric sesquidiploid hybrids (2 genomes ofL. esculentumand 1 ofS. lycopersicoides) were pollinated withLycopersicon pennelliiderived bridging lines, yielding diploid, aneuploid (up to 2n+ 6), and polyploid (3x, 4x) progeny. After diploids (58% of total progeny), the group most frequently obtained was 2n+ 1 (31%), which included all 12 possible monosomic alien addition lines (MAALs) containing a single extra chromosome fromS. lycopersicoidesin a tomato background. MAAL groups were identified with a combination of allozyme, RFLP, and monogenic visual markers. Transmission rates of the extra chromosomes in MAALs varied from 0%, for chromosome 6, to 24%, for chromosome 10. At diakinesis and metaphase I of meiosis, the alien chromosome was usually unpaired (in an average of 90% of PMCs), but association of homoeologous chromosomes was observed in each of the 12 MAAL groups (in an average of 5.7% of PMCs). The MAALs showed a striking morphological resemblance to the corresponding tomato primary trisomic. In addition, each MAAL expressedS. lycopersicoidesspecific leaf, flower, and (or) fruit characters. This set of MAALs, the first of its kind inLycopersicon, is expected to be useful for a variety of gene-mapping and introgression studies.

ISSN:0831-2796    

DOI:10.1139/g97-095

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The surface-spreading synaptonemal complex (SC) technique was used to visualize the process of chromosome synapsis in white sturgeon spermatocytes. Pachytene nuclei had various numbers of univalents (0-3) and self-paired foldback elements with no obvious centromeric region (1-7) that may represent accessory chromosomes. The total SC length was 482 ( ±56) µm and the average number of SC elements per nucleus was 139 ( ±3.4). This SC number suggests a higher chromosome number than had been reported in previous mitotic studies (2n= 248 ± 8). There was variation in the SC count both within and between animals. A representative SC karyotype is presented and some differences between the mitotic and meiotic karyotypes for this species are discussed. There was no evidence of multivalent formation, suggesting that the process of diploidization has gone to completion in the males of this ancient polyploid species. Each SC had lateral elements of equal length, and no bivalent exhibited the atypical pairing behavior that is often characteristically associated with heteromorphic sex chromosomes, suggesting that the male is not the heterogametic sex in white sturgeon.

ISSN:0831-2796    

DOI:10.1139/g97-101

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Arabidopsis thaliana(the model dicotyledonous plant) is closely related toBrassicacrop species. Genome collinearity, or conservation of marker order, betweenBrassica napus(oilseed rape) andA. thalianawas assessed over a 7.5-Mbp region of the long arm ofA. thalianachromosome 4, equivalent to 30 cM. Estimates of copy number indicated that sequences present in a single copy in the haploid genome ofA. thaliana(n= 5) were present in 2-8 copies in the haploid genome ofB. napus(n= 19), while sequences present in multiple copies inA. thalianawere present in over 10 copies inB. napus. Genetic mapping inB. napusof DNA markers derived from a segment ofA. thalianachromosome 4 revealed duplicated homologous segments in theB. napusgenome. Physical mapping inA. thalianaof homologues ofBrassicaclones derived from these regions confirmed the identity of six duplicated segments with substantial homology to the 7.5-Mbp region of chromosome 4 inA. thaliana. These six duplicatedBrassicaregions (on average 22cM in length) are collinear, except that two of the six copies contain the same large internal inversion. These results have encouraging implications for the feasibility of shuttling between the physical map ofA. thalianaand genetic maps ofBrassicaspecies, for identifying candidate genes and for map based gene cloning inBrassicacrops.

ISSN:0831-2796    

DOI:10.1139/g97-097

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Insulin-like growth factor 1 (IGF1) regulates growth and metabolic functions in vertebrates. A dinucleotide repeat sequence located at the promoter region of the IGF1 gene has been reported in several vertebrate species and may affect the control of the transcriptional activity of this gene. The genotypes of animals from seven horse breeds were determined in order to study the potential association of allelic forms of this microsatellite with adult body size differences found in domestic horses. Among these breeds, five alleles were found. Breed-specific differences in adult body size could not be attributed to the presence or absence of any of the alleles observed. In addition, animals representing five other equid species were typed. Examples of apparent species-specific alleles were found. However, overlapping polymorphic size ranges preclude this microsatellite from being an absolute identifier for species or hybrid status in equids. The polymorphisms found at this IGF1 locus are useful for synteny and linkage mapping.

ISSN:0831-2796    

DOI:10.1139/g97-105

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

In the Mediterranean fruit fly,Ceratitis capitata, the sex-determining region maps to the long arm of the Y chromosome. DNA from this region of the Y chromosome and, for comparison, from the tip of the long arm of the X chromosome, was isolated by microdissection and amplified by degenerate oligonucleotide primer PCR (DOP-PCR). FISH of the Y-chromosomal microdissection products medY1-medY5 to mitotic chromosomes revealed hybridization signals on most of the long arm of the Y chromosome, including the male-determining region, and on the long arm of the X chromosome, as well as weaker signals on the autosomes, some of which were located in the heterochromatin next to the centromeres. The X-chromosomal microdissected probe medX1 revealed strong signals on the sex chromosomes and randomly distributed signals on the autosomes. Chromosomal in situ suppression hybridization indicates that the Y chromosome contains considerable amounts of Y-enriched and Y-specific sequences and that X-enriched sequences are present on the long arm of the X chromosome. The microdissected probes medY1, medY2, and medX1 hybridize to the sex chromosomes of two closely related species,Ceratitis rosaandTrirhithrum coffeae.

ISSN:0831-2796    

DOI:10.1139/g97-102

出版商:NRC Research Press    

年代:1998

数据来源: NRC