Showing papers in "Genome in 1989"
TL;DR: Large numbers of entries are now lodged in many of the world's germ-plasm collections of crop and pasture plants, and the problems of how best to conserve it and how to use it in plant breeding have intensified.
Abstract: Large numbers of entries are now lodged in many of the world's germ-plasm collections of crop and pasture plants This abundance of material, assembled to guard against its irretrievable loss, has
705 citations
TL;DR: Structural analysis of synthetic DNA oligonucleotides that are active as primers showed that they all formed discrete intramolecular foldback structures at temperatures below 40 degrees C, which is a model for telomere elongation by telomerase.
Abstract: Telomeres stabilize chromosomal ends and allow their complete replication in vivo. In diverse eukaryotes, the essential telomeric DNA sequence consists of variable numbers of tandem repeats of simp...
224 citations
TL;DR: Seventy varieties of rice, representing the breadth of the species Oryza sativa, were assayed with 10 rice restriction fragment length polymorphism markers and polymorphism was detected for all probes.
Abstract: Seventy varieties of rice, representing the breadth of the species Oryza sativa, were assayed with 10 rice restriction fragment length polymorphism markers. Polymorphism was detected for all probes and 58 of 70 varieties tested could be uniquely distinguished from one another by combining all probe – enzyme combinations. Within-population variation, usually in the form of homozygous variant alleles, was found for 26% of the varieties. Based on genetic distance calculations, the ratio of the genetic variation between versus within rice varieties was estimated to be approximately 12:1. A restriction fragment length polymorphism based dendrogram has also been constructed depicting genetic distances among rice varieties.Key words: Oryza sativa, rice, polymorphism, genetic variation, restriction fragment length polymorphism.
202 citations
TL;DR: Heterosis for total and marketable tuber yield and specific gravity occurs in 4x families from crosses between 4x cultivars and 2x haploid Tuberosum × 'Phureja' hybrids.
Abstract: Potato breeding methods that utilize haploids of Solanum tuberosum group Tuberosum or group Andigena and 2n gametes exploit the genetic diversity, including both valuable traits and allelic diversi
191 citations
TL;DR: The present status of the neutral theory is reviewed, including discussions of such topics as "molecular evolutionary clock," very high evolutionary rates observed in RNA viruses, a deviant coding system found in Mycoplasm together with the concept of mutation-driven neutral evolution, and the origin of life.
Abstract: The main tenet of the neutral theory is that the great majority of evolutionary changes at the molecular level are caused not by Darwinian selection but by random fixation of selectively neutral (or very nearly neutral) alleles through random sampling drift under continued mutation pressure. The theory also asserts that the majority of protein and DNA polymorphisms are selectively neutral, and that they are maintained in the species by mutational input balanced by random extinction rather than by "balancing selection." The neutral theory is based on simple assumptions. This enabled us to develop mathematical theories (using the diffusion equation method) that can treat these phenomena in quantitative terms and that permit theory to be tested against actual observations. Although the neutral theory has been severely criticized by the neo-Darwinian establishment, supporting evidence has accumulated over the last 20 years. In particular, the recent burst of DNA sequence data helped to strengthen the theory a great deal. I believe that the neutral theory triggered reexamination of the traditional "synthetic theory of evolution." In this paper, I review the present status of the neutral theory, including discussions of such topics as "molecular evolutionary clock," very high evolutionary rates observed in RNA viruses, a deviant coding system found in Mycoplasm together with the concept of mutation-driven neutral evolution, and the origin of life. I also present a worldview based on the conception of what I call "survival of the luckiest."
172 citations
TL;DR: Early seed development in crosses between the hexaploid wheat genotype 'Chinese Spring' and the maize genotypes was studied to determine the timing of elimination of the maize chromosomes, suggesting all maize chromosomes were lost during the first three cell-division cycles in most embryos.
Abstract: Early seed development in crosses between the hexaploid wheat genotype 'Chinese Spring' and the maize genotype 'Seneca 60' was studied to determine the timing of elimination of the maize chromosomes. Elimination of one or more maize chromosomes occurred in about 70% of zygotic mitoses. Metaphase nuclei from two-celled embryos had 5 to 10 maize chromosomes, most of which were lost during the second cell division. About half the metaphase nuclei from four-celled embryos had no maize chromosomes, and the remainder had one to five. Anaphase or telophase nuclei from four-celled embryos showed no maize chromosomes in about half the cells and one or more pairs of lagging maize daughter chromosomes in the remainder. No maize chromosomes were seen in metaphase preparations from embryos with eight or more cells. These data strongly suggest that all maize chromosomes were lost during the first three cell-division cycles in most embryos. All embryos with four or more cells had micronuclei, showing that embryo develop...
148 citations
TL;DR: The use of restriction fragment length polymorphisms (RFLPs) as genetic markers in bread wheat, Triticum aestivum, and a wild wheat progenitor, Aegilops squarrosa, was investigated to identify RFLP loci and to assign cDNA sequences onto specific chromosomes and chromosome arms.
Abstract: The use of restriction fragment length polymorphisms (RFLPs) as genetic markers in bread wheat, Triticum aestivum, and a wild wheat progenitor, Aegilops squarrosa, was investigated. The objectives ...
146 citations
TL;DR: Analysis of regenerated Zea mays plants of the inbred line A188 shows that a high proportion of the regenerants demonstrate significant alterations in the methylation status of both housekeeping and structural genes.
Abstract: Regeneration of plants via tissue culture often results in a number of plants subsequently showing phenotypic or genotypic deviations from the parental type This variation has been called somaclon
118 citations
TL;DR: The umbellulatum for 'Chinese Spring' chromosomes were used to identify chromosomal loci of 5S rRNA genes (5S DNA) in wheat and related species and concerted evolution of the 5S DNA loci was examined in several genomes.
Abstract: Variation in restriction fragments in nullisomic–tetrasomic and ditelosomic lines of Triticum aestivum 'Chinese Spring' and disomic and ditelosomic substitutions of chromosomes of diploid species Lophopyrum elongatum, T. monococcum ssp. aegilopoides, T. tauschii, and T. umbellulatum for 'Chinese Spring' chromosomes were used to identify chromosomal loci of 5S rRNA genes (5S DNA) in wheat and related species. These loci are on wheat chromosome arms 1BS, 1DS, 5AS, 5BS, and tentatively 5DS, T. m. aegilopoides chromosomes 1A and 5A, T. tauschii chromosomes 1D and 5D, and T. umbellulatum chromosome 5U. In diploid L. elongatum a locus was detected on chromosome arm 1ES. In most genomes, the locus on chromosome 1 contains 5S DNA subfamily with short spacers and the locus on chromosome 5 contains 5S DNA subfamily with long spacers. Only a few genomes were found to be potential exceptions to this rule. Concerted evolution of the 5S DNA loci was examined in several genomes. It appeared that homogenization of spacer...
118 citations
TL;DR: Drosophila subobscura is a Palearctic species that has been extensively studied by population and evolutionary geneticists for nearly half a century, and all evidence indicates that both the North American and the South American colonizers derive from the samePalearctic population.
Abstract: Drosophila subobscura is a Palearctic species that has been extensively studied by population and evolutionary geneticists for nearly half a century. In 1978, it appeared in Puerto Montt, Chile; wi...
TL;DR: Results of the analyses show that both natural selection and random drift are important for the origin of gene families, and interaction between molecular mechanisms such as unequal crossing-over and gene conversion, and selection or drift is found to have a large effect on evolution by gene duplication.
Abstract: It is now known that many multigene and supergene families exist in eukaryote genomes: multigene families with uniform copy members like genes for ribosomal RNA, those with variable members like immunoglobulin genes, and supergene families such as those for various growth factor and hormone receptors. Many such examples indicate that gene duplication and subsequent differentiation are extremely important for organismal evolution. In particular, gene duplication could well have been the primary mechanism for the evolution of complexity in higher organisms. Population genetic models for the origin of gene families with diverse functions are presented, in which natural selection favors those genomes with more useful mutants in duplicated genes. Since any gene has a certain probability of degenerating by mutation, success versus failure in acquiring a new gene by duplication may be expressed as the ratio of probabilities of spreading of useful versus detrimental mutations in redundant gene copies. Also examined are the effects of gene duplication on evolution by compensatory advantageous mutations. Results of the analyses show that both natural selection and random drift are important for the origin of gene families. In addition, interaction between molecular mechanisms such as unequal crossing-over and gene conversion, and selection or drift is found to have a large effect on evolution by gene duplication.
TL;DR: Eight imidazolinone herbicide resistant corn cell lines were obtained from in vitro cell culture selections and plants were regenerated from five of the lines and resistant progeny obtained from four, which showed cross resistance to a sulfonylurea herbicide.
Abstract: Eight imidazolinone herbicide resistant corn cell lines were obtained from in vitro cell culture selections. Plants were regenerated from five of the lines and resistant progeny obtained from four....
TL;DR: The mutation–selection balance, genetic variability, continuum-of-alleles model, house- of-cards approximation is reviewed, with the intention of simplifying it as much as possible.
Abstract: Metric characters closely connected with fitness have little additive genetic variability, presumably because it is quickly exhausted under continuous directional selection on fitness. Other metric...
TL;DR: Both approaches allow embryos to be cloned, but whereas blastomere separation allows only a relatively small number of genetically identical animals to be produced, nuclear transplantation will probably open the way for large-scale cloning of livestock.
Abstract: The results of experiments aimed at cloning of sheep and cattle embryos are described. Two experimental approaches were used to study the developmental potential of blastomeres from sheep and cow e...
TL;DR: The role of specific gene products and nuclear structures in meiotic chromosome behavior in yeast was investigated in a single experimental system using a combination of genetic, molecular cloning, and cytological approaches.
Abstract: Both meiosis-specific and general recombination functions, recruited from the mitotic cell cycle, are required for elevated levels of recombination and for chromosome synapsis (assembly of the synaptonemal complex) during yeast meiosis. The meiosis-specific SPO11 gene (previously shown to be required for meiotic recombination) has been isolated and shown to be essential for synaptonemal complex formation but not for DNA metabolism during the vegetative cell cycle. In contrast, the RAD52 gene is required for mitotic and meiotic recombination but not for synaptonemal complex assembly. These data suggest that the synaptonemal complex may be necessary but is clearly not sufficient for meiotic recombination. Cytological analysis of spread meiotic nuclei demonstrates that chromosome behavior in yeast is comparable with that observed in larger eukaryotes. These spread preparations support the immunocytological localization of specific proteins in meiotic nuclei. This combination of genetic, molecular cloning, and cytological approaches in a single experimental system provides a means of addressing the role of specific gene products and nuclear structures in meiotic chromosome behavior.
TL;DR: Only in some early spermatids could the 190, 30, and 33-kDa polypeptides be detected, presumably in remnants of synaptonemal complexes be detected.
Abstract: Synaptonemal complexes were isolated from rate spermatocytes for the purpose of biochemical and morphological analysis Several monoclonal antibodies were elicited against purified synaptonemal com
TL;DR: This correspondence of individual homeoboxes in different chromosomal loci suggests the hypothesis of large-scale duplications of a single complex locus, which might have predated the divergence of vertebrates and invertebrates.
Abstract: We report the genomic organization of 20 human class I homeoboxes and the predicted primary sequence of the encoded homeodomains. These homeoboxes are clustered in four complex HOX loci on chromoso...
TL;DR: Research is outlined attempting to use high frequency chromosomal interchanges in wheat cell cultures to introgress genes from alien chromosomes, suggesting that the resistance, but not other alien markers, is now on a wheat chromosome.
Abstract: Plants from cell cultures show a high incidence of mutation. The causes of somaclonal variation are unknown, but the genetic consequences have been analysed. A range of genetic events are responsib...
TL;DR: In many Simuliidae, patterns of spatial and temporal relationships among the most closely related species are more readily interpreted in terms of sympatricSpeciation than of allopatric speciation.
Abstract: In many Simuliidae, patterns of spatial and temporal relationships among the most closely related species are more readily interpreted in terms of sympatric speciation than of allopatric speciation. Specific examples are (i) the allotriploid taxa in Gymnopais and other genera, (ii) the black fly faunas of geologically recent islands (Tahiti), and (iii) species in Prosimulium onychodactylum, a prototype of a continental multisibling species complex. A model of sympatric speciation is presented based on coadaptation of polymorphic sex chromosomes in pairs reinforced by progressive development of assortative mating. This model predicts that (i) populations should frequently exhibit sex-chromosome polymorphism, (ii) these sex-chromosome polymorphisms, and autosomal ones, should in some cases display linkage or association disequilibria, (iii) species pairs or complexes should be incurred that differ only in sex chromosomes and that share extensive ancestral autosomal polymorphisms, and (iv) such species shoul...
TL;DR: It is reported that the distribution of exchanges along the chromosome of Red−Gam−phage λ is strikingly altered by recD null mutations in the host, and recombination in recD mutant strains is high near λ's right end.
Abstract: RecBCD enzyme is centrally important in homologous recombination in Escherichia coli and is the source of ExoV activity. Null alleles of either the recB or the recC genes, which encode the B and C ...
TL;DR: Interspecific hybrids between three breeding lines of Oryza sativa and 18 accessions of O. officinalis obtained through an embryo-rescue technique showed a low amount of chromosome pairing and were completely male sterile.
Abstract: Interspecific hybrids between three breeding lines of Oryza sativa (2n = 24 = AA) and 18 accessions of O. officinalis (2n = 24 = CC) were obtained through an embryo-rescue technique. The crossabili...
TL;DR: The results suggest that most of the TGRI clusters consist of single, uninterrupted blocks of satellite DNA, close to the estimated total length of TGRI in the genome based on genomic reconstruction experiments.
Abstract: A karyotype of tomato mitotic chromosomes was constructed based on in situ hybridization to a 162-bp telomeric DNA repeat, TGRI. Variation in the spatial and quantitative distribution of this repeat creates distinct patterns for most of the chromosomes, which along with other morphological characteristics (i.e., length and arm length ratio), allow the identification of each of the 12 mitotic chromosomes of tomato. The structure and physical size of the TGRI clusters were further investigated by means of pulsed-field gel electrophoresis. Approximately 30 hybridizing fragments were observed in the range of 25 to 1000 kb when high molecular weight DNA was digested with BglII and probed with TGRI. The total molecular weight of these fragments is approximately 14 million bp, which is close to the estimated total length of TGRI in the genome (12.5 million bp) based on genomic reconstruction experiments. The results suggest that most of the TGRI clusters consist of single, uninterrupted blocks of satellite DNA. ...
TL;DR: Nucleotide sequence alignment of 5S DNA repeat units from a number of Secale species, using both phenetic and cladistic computer programmes, demonstrated that two clear lineages corresponding to the long and short units existed in this genus.
Abstract: The 5S RNA genes in Secale sp. are arranged as tandem arrays of a 460- and 480-bp repeating sequence. These size classes were initially discovered by restriction endonuclease analysis using BamHI a...
TL;DR: The presence of multiple binding sites within single MARs may allow DNA and RNA polymerase passage without disrupting primary loop organization, and the sites most susceptible to topoisomerase II cleavage are localized near the breakpoints of a previously described illegitimate recombination event.
Abstract: We have recently identified an evolutionarily conserved class of sequences that organize chromosomal loops in the interphase nucleus, which we have termed "matrix association regions" (MARs). MARs ...
TL;DR: In a survey of 107 alfalfa genotypes, the dominant and recessive alleles were present in equal frequencies and Embryogenesis among those plants producing callus was controlled by two complementary loci with additivity within each locus.
Abstract: To study the inheritance of somatic embryogenesis in alfalfa (Medicago sativa L.), three alfalfa genotypes were self-pollinated and intercrossed. A70-34 is a highly embryogenic genotype; R3 produced callus but not embryos; and MK does not produce callus. Callus production was controlled by one locus with complete dominance. In a survey of 107 alfalfa genotypes, the dominant and recessive alleles were present in equal frequencies. Embryogenesis among those plants producing callus was controlled by two complementary loci with additivity within each locus. The suggested designations for the two genes are Rna and Rnb.Key words: alfalfa, Medicago sativa L., tissue culture, somatic embryogenesis, inheritance.
TL;DR: Parsimony and maximum likelihood analyses, carried out on orthologous noncoding nucleotide sequences from primate beta-globin gene clusters, provide significantevidence for the human-chimpanzee tribe and overwhelming evidence for thehuman-chicpanzee-gorilla clade, and indicate that the rate of molecular evolution became slower in hominoids than in other primates and mammals.
Abstract: The morphological picture of primate phylogeny has not unambiguously identified the nearest outgroup of Anthropoidea and has not resolved the branching pattern within Hominoidea. The molecular pict...
TL;DR: Contact between appropriate mycorrhizal symbionts initiates a cascade of events that leads to modifications in the behaviour of both organisms at cell and tissue levels and the establishment of a symbiotic relationship.
Abstract: Contact between appropriate mycorrhizal symbionts initiates a cascade of events that leads to modifications in the behaviour of both organisms at cell and tissue levels and the establishment of a f...
TL;DR: The relative amount of C-banded heterochromatin varies strikingly in seven species of tenebrionid beetles, from 25 to 58%, but most species show procentric bands only, and the genome sizes agree with the subfamilial taxonomic groupings of these tenesbrionids.
Abstract: The relative amount of C-banded heterochromatin varies strikingly in seven species of tenebrionid beetles, from 25 to 58%, but most species show procentric bands only. Nevertheless, Gonocephalum pa...
TL;DR: It is postulated here that mismatch-stimulated antirecombination by long-patch mismatch repair is a "proofreading" system assuring high fidelity of homologous recombination, which accounts for chromosomal stability in eucaryotes and provides a molecular mechanism for speciation without the necessity of geographical separation.
Abstract: Two modes of mismatch repair are known to operate in bacteria: long-patch mismatch repair and very short patch mismatch repair. Very short patch mismatch repair systems act on a specific mismatch b...