摘要:

This research reports a new technique for chromosome doubling of clover (Trifoliumsp.) axillary meristems viain vitrocolchicine application. Plant material utilized includedT.pratense(red clover) cv. Kenstar clones, and three interspecific hybrids:T.ambiguum(kura clover) ×T.repens(white clover);T.alpestre×T.pratense; andT.sarosiense×T.pratense. Vegetative axillary meristems were excised from plants, surface sterilized, and trimmed to a length of 0.5–1 mm. Meristems were placed on the surface of a shoot proliferation medium (ML8) containing colchicine (0.1%) for 48 or 72 h and then transferred back to ML8. Alternative treatments were to preculture meristems on ML8 for 7 days prior to colchicine treatment. Plantlets with two or three trifoliolate leaves were induced to root on CR2 or RL rooting media. Preculturing of meristems on ML8 prior to colchicine exposure resulted in the highest chromosome doubling frequencies among the different genotypes, although there was apparent genotype × treatment interaction. Chromosome doubling frequencies were as high as 81 and 44% for initial root tips and mature shoots, respectively. To make rapid assessments of ploidy level of flowering plants, pollen shape was examined. Chromosome doubling increased the pollen stainability of theT.ambiguum×T.repenshybrid from 2.5 to 33.6%, but did not result in fertility in the other two interspecific hybrids.Key words:Trifolium, colchicine, chromosome doubling, interspecific hybrids.

ISSN:0831-2796    

DOI:10.1139/g91-001

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

In this paper we present the sequence of an intactCaenorhabditis briggsaetransposable element, Tcb2. Tcb2 is 1606 base pairs in length and contains 80 base pair imperfect terminal repeats and a single open reading frame. We have identified blocks of T-rich repeats in the regions 150–200 and 1421–1476 of this element which are conserved in theCaenorhabditis eleganselement Tc1. The sequence conservation of these regions in elements from differentCaenorhabditisspecies suggests that they are of functional importance. A single open reading frame corresponding to the major open reading frame of Tc1 is conserved among Tc1, Tcb1, and Tcb2. Comparison of the first 550 nucleotides of the sequence among the three elements has allowed the evaluation of a model proposing an extension of the major open reading frame. Our data support the suggestion that Tc1 is capable of producing a 335 amino acid protein. A comparison of the sequence coding for the amino and carboxy termini of the 273 amino acid transposase fromCaenorhabditisTc1-like elements andDrosophilaHB1 showed different amounts of divergence for each of these regions, indicating that the two functional domains have undergone different amounts of selection. Our data are not compatible with the proposal that Tc1-related sequences have been acquired via horizontal transmission. The divergence of Tc1 from the twoC.briggsaeelements, Tcb1 and Tcb2, indicated that all three elements have been diverging from each other for approximately the same amount of time as the genomes of the two species.Key words:Caenorhabditis, transposable element, sequence comparison.

ISSN:0831-2796    

DOI:10.1139/g91-002

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Karyological analysis of C- and G-banding patterns of 44 specimens ofHolochilus venezuelaerevealed six distinct karyomorphs, which were designated as follows: I (2n = 44; fundamental number (FN) = 56); II (2n = 45; FN = 58); IV (2n = 43; FN = 56);V(2n = 44; FN = 58); IV-a(2n = 42; FN = 56); and V-a (2n = 44; FN = 58). This chromosomal polymorphism is interpreted as the result of (i) one or two Robertsonian changes of the centric-fusion type, originating from one member of chromosome pair 10 and one of pair 11 (in karyotypes IV and V) and two metacentric chromosomes from pairs 10 and 11 (in karyotype IV-a); (ii) one pericentric inversion (in karyotype V-a) forming one submetacentric chromosome from the metacentric fusion product described above; and (iii) the presence of B chromosomes, which are almost completely heterochromatic and do not pair with any member of group A. The pattern of C-banding reveals that the first five pairs of metacentric chromosomes contain very little centromeric heterochromatin, while pair 6 and the fusion chromosomes (10/11 F) present a thick band. Extensive homology was found between G-banding patterns ofHolochilus brasiliensisfrom Brazil andH.venezuelae. These facts support the hypothesis of a karyotypic evolution via centric fusions previously proposed for this genus.Key words: accessory chromosome, C- and G-banding, polymorphism,Holochilus venezuelae.

ISSN:0831-2796    

DOI:10.1139/g91-003

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The behaviour of two chromosome structures in silver-stained chromosomes was analyzed through the first meiotic division in spermatocytes of the acridoid speciesArcyptera fusca. Results showed that at diakinesis kinetochores and chromatid cores are individualized while they associate in bivalents of metaphase I; only kinetochores and distal core spots associate in the sex chromosome. Metaphase I is characterized by morphological and localization changes of both kinetochores and cores which define the onset of anaphase I. These changes analyzed in both autosomes and in the sex chromosome allow us to distinguish among three different substages in metaphase I spermatocytes. B chromosomes may be present as univalents, bivalents, or trivalents. Metaphase I B univalents are characterized by separated cores except at their distal ends and individualized and flat sister kinetochores. At anaphase I sister kinetochores of lagging B chromatids remain connected through a silver-stained strand. The behaviour of cores and kinetochores of B bivalents is identical with that found in the autosomal bivalents. The differences in the morphology of kinetochores of every chromosome shown by B trivalents at metaphase I may be related to the balanced forces acting on the multivalent. The results show dramatic changes in chromosome organization of bivalents during metaphase I. These changes suggest that chromatid cores are not involved in the maintenance of bivalents. Moreover, the changes in morphology of kinetochores are independent of the stage of meiosis but correlate with the kind of division (amphitelic–syntelic) that chromosomes undergo.Key words: kinetochore, chromatid core, B chromosomes, meiosis, chromosome structure, silver staining.

ISSN:0831-2796    

DOI:10.1139/g91-004

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Computer simulation was undertaken to compare the genetic consequences of asexual (somatic doubling) and sexual (2ngametes) polyploidization. The coefficient of inbreeding at a locus, the number and frequency of genotypes at a locus, and the proportion of tri- and tetra-allelic genotypes were considered. The factors considered to estimate the genetic consequences were (i) mechanisms of sexual polyploidization, by first division restitution (FDR) × second division restitution (SDR), FDR × FDR, or SDR × SDR; (ii) position of the locus in relation to the centromere, which affects the gametic output in 2ngamete formation and thus the probability of single-exchange tetrads in meiosis during 2ngamete formation (pvalue); and (iii) allelic diversity at a locus. In comparing asexual and sexual polyploidization, regardless of the position of a locus in relation to the centromere, sexual polyploidization generally indicated less inbreeding, more genotypic diversity, and a higher proportion of tri- and tetra-allelic genotypes. When allelic diversity at a locus was increased, these characteristics were even more prominent. When only two alleles are possible at a locus, somatic doubling would not be inferior to sexual polyploidization. Overall results favored SDR × FDR and FDR × FDR as a mode and mechanisms of polyploidization. The genetic variations produced by 2ngametes could be attributed to "combining ability of 2ngametes."Key words: asexual polyploidization, sexual polyploidization, inbreeding, heterozygosity, combining ability of 2ngametes.

ISSN:0831-2796    

DOI:10.1139/g91-005

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Mutable alleles, typically regulated by transposable elements, have been identified in a number of plant species. Tissue culture induced genomic shocks may activate such elements. A mutable recessive condition arose in tissue culture of alfalfa and was highly unstable in subsequent cycles of culture. The mutable allele, designatedc2-m4, is allelic to theC2locus, a basic color factor locus involved in anthocyanin synthesis. Current research has focused on the inheritance and instability ofc2-m4in new genetic backgrounds as well as on dosage effects of the allele. We have confirmed a previous report thatc2-m4reverts to function at much higher frequenciesin vitro(reversion frequency ca. 0.23) thanin planta(reversion frequency < 0.001). Over sexual generationsc2-m4continues to be unstable. Transmission of the mutable phenotype to selfed, testcross, and F2populations demonstrated monofactorial inheritance patterns (P > 0.25). In populations expected to have some plants carrying two or morec2-m4alleles, individuals were found that revertedin vitroat significantly higher frequencies than their parent (0.67 ± 0.04 and 0.44 ± 0.08 versus 0.20 ± 0.09).In plantareversion also increased with increasingc2-m4dosage. Preliminary evidence indicates that asc2-m4dosage increases, each allele maintains its original capacity to revert.Key words: somaclonal variation, transposable element, tissue culture, mutable allele.

ISSN:0831-2796    

DOI:10.1139/g91-006

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A cryptorchid male mouse with 41,XXY chromosome constitution was found in 300 male offspring that were born to our XO mice breeding colony. This individual had small testes with no sign of spermatogenesis at autopsy at 10 months of age.Key words: 41,XXY, mouse, XO mice colony, testes, spermatogenesis.

ISSN:0831-2796    

DOI:10.1139/g91-007

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Analysis of NADH dehydrogenase isozymes in hexaploid wheat (Triticum aestivum) by flat-bed isoelectric focusing revealed a genetic system involving four sets ofNdhloci. TheNdh-A1locus, previously identified on chromosome arm 4AL, was confirmed. HomoeolociNdh-R1in rye,Ndh-H1in barley,Ndh-Hch1inHordeum chilense,Ndh-Sl1inAegilops sharonensis, andNdh-V1inDasypyrum villosumwere also identified. TheNdh-2loci, encoding monomeric isozymes, were found in the short arms of homoeologous group 7 chromosomes. HomoeolociNdh-A2,Ndh-D2, andNdh-R2are described. TheNdh-3set, encoding multimeric isozymes, were found on each of the homoeologous group 3 chromosome long arms. AnNdh-B3bvariant and homoeolociNdh-R3(on chromosome arm 6RL),Ndh-H3, andNdh-Sl3are described. TheNdh-4set, encoding monomeric isozymes for which no varietal variation was found, were identified on the short arms of group 3 chromosomes.Ndh-A4,Ndh-B4,Ndh-H4,Ndh-R4, andNdh-E4(Agropyron elongatum) homoeoloci are described.Key words: NADH dehydrogenase, isozymes, wheat, Triticeae.

ISSN:0831-2796    

DOI:10.1139/g91-008

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

In an attempt to know the phylogeny of timothy (Phleum pratense), the cultivated species and two wild relatives,Phleum alpinumandPhleum bertolonii, were karyotyped with conventional and Giemsa C-banding methods. In the hexaploidP.pratense(2n = 6x = 42), two sets of seven chromosomes were indistinguishable from each other both in morphology and in banding patterns and the third set of seven was found to be differentiated from them. Two genomes, A and B, were tentatively established. The banded karyotype in diploidP.alpinum(2n = 2x = 14) was close to the A genome, which was tetraploid inP.pratense, and the karyotype inP.bertolonii(2n = 2x = 14) was analogous to the B genome inP.pratense, which suggests these species were the genome donors ofP.pratense.Key words: chromosome, genome, allopolyploid, Giemsa C-banding.

ISSN:0831-2796    

DOI:10.1139/g91-009

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A study was made of the phosphoglucoisomerase (PGI/2) phenotype of plants regenerated from suspension and protoplast culture originating from aFestuca arundinacea(2n = 6x = 42) plant with distinct PGI/2 phenotype. Of the regenerated plants from suspension culture, 20 were abnormal in that they deviated from the PGI/2 phenotype of the donor plant. Among the abnormal plants two distinct isozyme variants absent in the original donor, which were probably the result of point mutations, were recorded. There was evidence of deletions of specific PGI/2 alleles. This was confirmed cytologically by the reduced chromosome number found in the relevant cell suspension derived plants. There was also evidence that an active allele had been transformed into a null allele. All the plants regenerated from protoplast culture had the same PGI/2 phenotype as the donor plant but were hyperpolyploid. The loss of activity of individual PGI/2 alleles in plants derived from protoplasts was masked by gene duplication because of their hyperpolyploid nature. A high degree of instability was identified in nonregenerating calli. It was thought that abnormalities in the nonregenerating calli were affecting their potential to regenerate plants.Key words:Festuca arundinacea, somaclonal variation, phosphoglucoisomerase (PGI/2), chromosome instability, point mutations.

ISSN:0831-2796    

DOI:10.1139/g91-010

出版商:NRC Research Press    

年代:1991

数据来源: NRC