摘要:

Seed of flax (Linum usitatissimum) were treated for short durations with 5-azacytidine and the direct and heritable effects of the treatments on plant growth and development in general and, more specifically, on the contrasting phenotypes of Durrant's large and small genotrophs were examined. 5-Azacytidine induced a reduction in the height of the plants grown from treated seed. Twenty-two percent of the first generation progeny of these plants also had short phenotypes and, in most cases, the short phenotype was stably and uniformly inherited by the second generation progeny of the short, first generation plants. Treatment also induced a marked decrease in the flowering age in a few of the first generation plants that was also transmitted to their second generation progenies. The effects seen in the progeny generations suggest that most, if not all, of the heritable changes induced by the treatment are epigenetic. Several differences were seen between the large and small genotrophs, which indicate that the genome of the small genotroph is less susceptible, than the genome of the large genotroph, to 5-azacytidine induced heritable alterations.Key words: flax genotrophs, 5-azacytidine, height, flowering.

ISSN:0831-2796    

DOI:10.1139/g94-001

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The 2-μm plasmid of industrial and laboratory strains ofSaccharomyces cerevisiaeexists as two main polymorphic forms designated type I and type II. Polymorphism is restricted to the 3200-bp right unique region where types I and II show approximately 10% nucleotide divergence in trans-actingREP1andRAFloci and 30% divergence in the cis-actingSTBlocus. In addition, the cis-actingSTBplasmid partition locus of type II plasmids varies in sequence and copy number of a 125-bp repeat. We devised chimeric and 2-μm plasmid stability experiments to evaluate the effect ofSTBpolymorphism on plasmid fitness in amphiploid industrial and haploid laboratory strains. Reciprocal experiments of type-IISTBchimeric plasmids in type-I bakers' yeast or a type-I chimeric plasmid in type-II distillers', wine, or haploid strains showed similar partition efficiencies. However, chimeric and 2-μm plasmids carrying a 250-bpSTBfrom a type-II haploid strain had reduced fitness in a type-II industrial wine strain. These results in conjunction with molecular analyses of 2-μm-like and 2-μm plasmids indicates the coevolution ofSTBwith trans-acting plasmid and host-cell factors.Key words:Saccharomyces cerevisiae, 2-μm plasmid,STBadaption.

ISSN:0831-2796    

DOI:10.1139/g94-002

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Sequences derived from a rye gamma secalin gene were used as primers in polymerase chain reactions using DNA obtained from a series of wheat and triticale genetic stocks. A 473-bp fragment, the predicted size based on the distance between the selected primers, was found only in rye, triticales, and wheat lines carrying rye chromosome 2RS. Use of triticale lines with various wheat chromosome substitutions confirmed the chromosomal origin of the rye-specific marker. The presence of the 473-bp PCR product was always associated with the production of 75K secalins in grain samples. Thus, the primer sequences, and the clone of origin (pSC503), were both derived from theSEC-2locus of rye chromosome 2RS.Key words: wheat (Triticum aestivum), rye (Secale cereale), chromosomal translocations, chromosomal substitutions, DNA polymerase chain reaction, sequence-specific primers.

ISSN:0831-2796    

DOI:10.1139/g94-003

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The 17S/5.8S/26S ribosomal DNA (rDNA) sequences were mapped to the three satellited (SAT) chromosomes in the common hexaploid cultivated oatAvena sativa(2n = 6x = 42, AACCDD genomes). In situ hybridization and Southern hybridization of maize and (or) wheat rDNA probes to DNA from nullisomics derived from the cultivar 'Sun II' allowed the placement of rDNA sequences to the physical chromosomes. A restriction map was produced for the rDNA sequences of 'Sun II' using a maize probe from the transcribed region of the 17S/26S rDNA repeat. The set of rDNA repeats on SAT 2 of 'Sun II' possesses a 10.5-kbEcoRI fragment not found in the rDNA repeats of SAT 1 and SAT 8. This 10.5-kb fragment results from the absence of anEcoRI site in the intergenic spacer (IGS) of SAT 2 repeats. Extensive polymorphisms were demonstrated for three hexaploidAvenaspecies, namely, the Mediterranean-type cultivated oatA.byzantinaand the wild speciesA.sterilisandA.fatua. However, geographically diverseA.sativacultivars displayed little rDNA variation. In contrast with all of theA.sativacultivars examined, theA.sterilisaccessions generally lacked the 10.5-kbEcoRI fragment. The results support the hypothesis thatA.sativaaccessions descend from a limited ancestral cultivated population. The rDNA polymorphisms are attributed to differences in lengths and restriction sites of the IGS.Key words: oats, rDNA, RFLPs, nullisomics, in situ hybridization.

ISSN:0831-2796    

DOI:10.1139/g94-004

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Three lines of obligately parthenogeneticDaphniawere allowed to diverge for a 4-year period (approximately 150 generations) with mutation as the sole source of variability. Life-history traits and morphological characters were then surveyed for between-line differences. Significant divergence was found with respect to both number and size of offspring, with no difference in total offspring biomass. No significant differences were found in any of the other characters. These results confirm the hypothesis that purely asexual lines can accumulate enough polygenic variation via mutation to support potentially adaptive changes on a microevolutionary time scale.Key words:Daphnia, life-history trait, mutational divergence, microevolution.

ISSN:0831-2796    

DOI:10.1139/g94-005

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A cytobiotaxonomic study of the medically important insect vectorSimulium ochraceums.l. revealed two sibling species and one cytotype from various endemic and nonendemic zones of human onchocerciasis in Guatemala and Mexico. Polytene chromosome maps and idiograms as well as notes on the biology of the three taxa designatedS.ochraceumA,S.ochraceumB, andS.ochraceumC within the subgenusPsilopelmiaare presented. All three taxa exhibit distinct sex chromosomes and taxon-specific suites of autosomal inversion polymorphisms.Simulium ochraceumC differs from bothS.ochraceumA andS.ochraceumB by five interspecific inversions designated IIS-7,8 and IIIL-12, 13 + 14, 15. The three taxa exhibit niche and biting preferences, withS.ochraceumA being highly anthropophilic. Analysis of autosomal inversion polymorphism profiles indicatesS.ochraceumA has long-range dispersal capability. Our results are consistent with the general findings that in the Simuliidae, sibling speciation may be suspected wherever a morphospecies occupies different niches in a stream continuum. We find for the first time an apparent partitioning of taxa by altitude.Simulium ochraceumA may be a primary vector of human onchocerciasis in Guatemala, as its vertical distribution is coincident with that of the highest areas of nodule prevalence in the human population. A genotypic component of variation in vectorial capacity ofS.ochraceumA populations seems to occur, since the Y4 chromosome and its X chromosome counterpart are associated with hyperendemic areas of human onchocerciasis. Our observation that a supernumerary band, 37B1Hb, is associated with sex determination in two of the taxa may be of significance for the elucidation of the molecular basis of sex determination and possible resolution of issues pertinent to the general model of sympatric speciation in the Simuliidae.Key words:Simulium ochraceumcomplex, cytobiotaxonomy, vector biology, sex chromosome evolution, human onchocerciasis.

ISSN:0831-2796    

DOI:10.1139/g94-006

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

In the tetraploid somatic hybrid between the diploidLycopersiconspeciesL.esculentum(tomato) andL.peruvianum, synaptonemal complexes formed quadrivalents in 73 of the 120 sets of four chromosomes (60.8%) in 10 cells studied in detail at pachytene. Of these, 43 had one pairing partner exchange, 22 had two, and 8 had three, very close to a Poisson distribution. The points of pairing partner exchange were concentrated at the middle of the two arms. The frequency per arm corresponded with physical arm length. There was a sharp drop around the centromere, and pericentric heterochromatin had a slightly lower probability of being involved in pairing partner exchange than euchromatin. The chromosomes align before pairing and there are several points of pairing initiation, with concentrations at or near the ends and the centromere. From zygotene to late pachytene the quadrivalent frequency decreased considerably. At late pachytene it was lower than expected with the observed high frequency of pairing partner exchange. Pairing affinity between species was only slightly lower than affinity within species, in spite of considerable genetic differentiation. The frequency of recombination nodules increased from early to late zygotene and then decreased strongly to full pachytene. There is a highly significant negative correlation between percent pairing and SC length. At metaphase I the frequency of quadrivalents was 0.444, and branched quadrivalents were rare, probably caused by interference and restriction of chiasma formation to distal euchromatin. Metaphase I quadrivalent frequency is a relatively good indication of pairing affinity in this material.Key words:Lycopersicon, tetraploid hybrid, synaptonemal complex, pairing partner exchange, diakinesis/metaphase I.

ISSN:0831-2796    

DOI:10.1139/g94-007

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A genome map of cultivated alfalfa was constructed using segregating restriction fragment length polymorphisms (RFLPs) and random amplified polymorphic DNAs (RAPDs) in a diploid backcross population generated from noninbred parents. Among the 153 loci scored in 87 progeny, four segregation ratios were observed for codominant and dominant markers: 1:1, 1:2:1, 1:1:1:1, and 3:1. Deviations from expected Mendelian ratios (p < 0.05) were observed for 34% of the loci studied. A genome map was assembled from two separate linkage maps, each constructed from a subset of the segregation data. One linkage map was constructed from 46 RFLP and 40 RAPD markers segregating 1:1 from the F1parent of the backcross and the other linkage map was constructed from 33 RFLP and 28 RAPD markers segregating 1:1 from the recurrent parent. Sixteen loci with alleles segregating 1:1 from both parents were used as locus bridges to align individual linkage groups between the two maps. The combined use of RFLPs and RAPDs was an effective method for developing an alfalfa genome map.Key words: genome mapping, RAPD, RFLP, locus bridges.

ISSN:0831-2796    

DOI:10.1139/g94-008

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

In the existing genetic sexing strains for the medfly,Ceratitis capitata, male recombination leads to breakdown of the sexing mechanism under mass rearing conditions. The rate of breakdown depends on the recombination frequency and on the fitness of the recombinants. We have tested two different sexing genes,white pupaand a temperature sensitive lethal, in combination with the translocation T(Y;5)30C. Both sexing strains broke down, although at very different rates. In the case of thewhite pupastrain, 3.5% recombinants were observed after rearing the strain for 15 generations. The second strain, utilizingwhite pupaand the temperature sensitive lethal as selectable markers, already reached a comparable level after six generations and was broken down completely in the ninth generation. In these strains the frequency of recombination is high because the breakpoint of T(Y;5)30C and the sexing gene(s) are far apart. To remedy the situation, we have isolated four new translocations with breakpoints located closer to the sexing genes. Mass rearing was simulated for several generations with strains based on these translocations and no breakdown was observed under the conditions used.Key words: medfly, sterile insect technique, genetic sexing, recombination.

ISSN:0831-2796    

DOI:10.1139/g94-009

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Chromosome pairing abnormalities in oocytes of bovine fetuses ranging in age from 81 to 130 days were studied using the surface-spread whole-mount technique. The synaptic abnormalities included partial or total asynapsis, nonhomologous pairing, and mid-pachytene degeneration with asynapsis constituting the most common category. Oocytes showing synaptic abnormalities were less frequent in younger fetuses and more abundant in fetuses older than 110 days. Histologic signs of oocyte degeneration, evident in all fetuses, were most striking in ovaries of fetuses older than 120 days. The temporal relationship of these events suggests that chromosome pairing anomalies may be associated with oocyte degeneration, although their exact role in precipitating oocyte atresia remains unclear. The presence of abnormal oocytes and follicles in the vicinity of the medullary cords seems to suggest that these germ cells may be exposed to deleterious substances from the degenerating rete cords and that the synaptic errors may be the meiotic manifestations of chromosome damages sustained by germ cells during the repeated oogonial divisions in an environment unconducive to mitosis and maturation of female germ cells.Key words: synaptonemal complex, cattle, female meiosis, oocyte degeneration.

ISSN:0831-2796    

DOI:10.1139/g94-010

出版商:NRC Research Press    

年代:1994

数据来源: NRC