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Introduction The genus Avena of the family Poaceae (Gramineae) is comprised of approximately 30 species (Baum 1977; Baum and Fedak 1985a, 1985b; Ladizinsky 1998) including three natural ploidy levels (diploid, [...], Genome size is an indicator of evolutionary distance and a metric for genome characterization. Here, we report accurate estimates of genome size in 99 accessions from 26 species of Avena. We demonstrate that the average genome size of C genome diploid species (2C = 10.26 pg) is 15% larger than that of A genome species (2C = 8.95 pg), and that this difference likely accounts for a progression of size among tetraploid species, where AB < AC < CC (average 2C = 16.76, 18.60, and 21.78 pg, respectively). All accessions from three hexaploid species with the ACD genome configuration had similar genome sizes (average 2C = 25.74 pg). Genome size was mostly consistent within species and in general agreement with current information about evolutionary distance among species. Results also suggest that most of the polyploid species in Avena have experienced genome downsizing in relation to their diploid progenitors. Genome size measurements could provide additional quality control for species identification in germplasm collections, especially in cases where diploid and polyploid species have similar morphology. Keywords: oat, flow cytometry, nucleus, polyploidy. La taille du genome est un indicateur de la distance evolutive et constitue un parametre pour la caracterisation des genomes. Ici, les auteurs rapportent des estimes precis de la taille du genome chez 99 accessions appurtenant a 26 especes du genre Avena. Les auteurs montrent que la taille moyenne du genome chez les especes diploides ayant un genome C (2C = 10,26 pg) est 15 % superieure a celui des especes ayant un genome A (2C = 8,95 pg), et que cette difference explique vraisemblablement la progression dans la taille des genomes parmi les especes tetraploides, ou AB < AC < CC (en moyenne, 2C = 16,76,18,60 et 21,78 pg, respectivement). Toutes les accessions des trois especes hexaploides ayant une composition genomique ACD presentaient des tailles de genome comparables (en moyenne, 2C = 25,74 pg). La taille du genome etait generalement stable au sein d'une espece, et conforme aux connaissances actuelles en ce qui a trait aux distances evolutives entre elles. Les resultats suggerent egalement que la plupart des especes polyploides du genre Avena ont connu une reduction de la taille du genome par rapport aux especes diploides ancestrales. Les mesures de la taille du genome pourraient fournir une source additionnelle de controle de qualite lors de l'identification des especes au sein de collections de ressources genetiques, particulierement dans les cas oU des especes diploides et polyploides presentent une morphologie semblable. [Traduit par la Redaction] Mots-cles : avoine, cytometrie en flux, noyau, polyploidie.

This paper reports the frequency of spontaneous amphiploids or neopolyploids in experimental interspecific hybrids in two annual sections of Gilia (Polemoniaceae, sects. Arachnion and Gilia, x = 9). In each section the species were intercrossed in numerous hybrid combinations to obtain an array of F1 hybrid types; seven of the hybrid types spontaneously produced new amphiploid progeny in F2. In sect. Arachnion the parental species and F1s were all diploids and the amphiploids were tetraploid; in sect. Gilia the parental species were diploids or tetraploids and the amphiploids were tetraploid or hexaploid. Two measures were used to express the frequency of spontaneous amphiploid formation. The first is the proportion of the F1 hybrid combinations that yielded any amphiploid progeny at all. In sect. Arachnion this proportion is 3/39 or 7.7%; in sect. Gilia it is 4/16 or 25%. A second measure is needed to express the variation in productivity among the seven amphiploid-producing hybrid types. The measure adopted is the mean number of new amphiploids per single F1 hybrid plant. The productivity numbers for the three hybrid combinations in sect. Arachnion are 0.25, 0.67, and 2.0; and those for four hybrid combinations in sect. Gilia are 0.15, 0.62, 2.25, and 12.62. There are large differences from one hybrid combination to another in rate of amphiploid formation, and the rate is quite high in some hybrids. The factors affecting these differences are discussed. Key words: amphiploidy; Gilia; Polemoniaceae; polyploidy rate.

Results show that tetraploids exhibit higher genetic diversity than the diploids. The Belgian Ardennes and within the mixed populations, diploids and tetraploids exhibit similar levels of spatial genetic structure, whereas in the European scale, they reveal a strong correlation between their spatial genetic variation patterns.

Research was conducted to understand influence of polyploidy on interspecific introgression and hybrid incompatibility in cotton plants. Results show that subgenomic interactions bring about unique characteristics to cotton plants that differentiate tetraploids from diploids.

The genetic structure of rock fern Asplenium csikii is compared with a related rock fern to understand population structure in the former. Results reveal that genetic diversity in A. csikii populations is not caused through multiple colonization. Instead, ecological specialization seem to contribute to their genetic variability.

Triploid females of social Hymenoptera may be more common than has been thought and are more likely to found in populations with substantial numbers of fertile diploid males than elsewhere. Origin and frequency of triploidy has been investigated in the fire ant Solenopsis invicta. A large microsatellite study has been made of fire ants of the two social types from native and introduced ranges, Argentina and the US. Surprisingly levels of triploidy, that is 12%, were found in nonreproductive females from an introduced polygyne population in the US. Triploid females were not found among reproductive queens from the same population, in females from monogyne populations in the introduced range or in females of either social type from the native range.

As part of a study aimed at elucidating the origins of the octoploid tuber crop 'oca.' Oxalis tuberosa, DNA sequences of the internal trancribed spacer of nuclear ribosomal DNA (nrDNA ITS) were determined for pea and several wild Oxalis species, mostly from Bolivia. Phylogenetic analysis of these data supports a group of these species as being close relatives of oca, in agreement with morphology and cytology, but at odds with traditional infrageneric taxonomy. Variation in ITS sequences within this group is quite low (0-7 substitutions in the entire ITS region), contrasting with the highly divergent (unalignable in some cases) sequences within the genus overall. Some groups of morphologically differentiated species were found to have identical sequences, notably a group that includes pea, wild populations of Oxalis that bear small tubers, and several other clearly distinct species. The presence of a second, minor sequence type in at least some oca accessions suggests a possible contribution from a second genome donor, also from within this same species group. ITS data lack sufficient variation to elucidate the origins of oca precisely, but have identified a pool of candidate species and so can be used as a tool to screen yet unsampled species for possible progenitors. Key words: crop evolution; domestication; nrDNA ITS: oca; Oxalidaceae; Oxalis tuberosa; polyploidy.

Immunofluorescent microscopic studies were utilized to establish the molecular and cellular mechanism of thrombopoietin (TPO)-induced polyploidization of megakaryocytes in vitro. Results have shown that multiple spindle poles were formed during polyploidization, simultaneously as polyploid megakaryocytes entered mitosis. Polyploidization was proven to be not caused merely by skipping mitosis and that megakaryocytes may mediate the regulatory mechanism involved in the polyploidization process.

We examined the inheritance of allelic variation at an isozyme locus, MDH-B, duplicated by ancestral polyploidy in salmonid fishes. We detected only disomic segregation in females. Segregation ratios in males were best explained by a mixture of disomic and tetrasomic inheritance. We propose a two-stage model of pairing in male meiosis in which, first, homologous chromosomes pair and recombine in the proximal region of the chromosome. Next, homeologous chromosomes pair and recombine distally. We suggest that this type of tetrasomic inheritance in which centromeres segregate disomically should be referred to as 'secondary tetrasomy' to distinguish it from tetrasomy involving entire chromosomes (i.e., 'primary tetrasomy'). Differences in segregation ratios between males indicate differences between individuals in the amount of recombination between homeologous chromosomes. We also consider the implication of these results for estimation of allele frequencies at duplicated loci in salmonid populations.

Meiotic behaviors and reproductive modes of Japanese Isoetes were studied. The hexaploid (2n = 66) and the octaploid (2n = 88) of I. japonica consistently formed 33 and 44 bivalents, respectively, at diakinesis and/or metaphase I in both micro- and megaspore mother cells. The tetraploid (2n = 44) of I. sinensis formed 22 bivalents and its hexaploid made 33 bivalents in both types of spore mother cells. At diakinesis and/or metaphase I of microspore mother cells in I. asiatica with 2n = 22, 11 bivalents were detected. Because behaviors of meiosis in all cytotypes mentioned above were quite regular and plants yielded normal-appearing spores, they should reproduce sexually. Aneuploids of I. japonica with 2n = 87 formed 43 bivalents and one univalent, and I. sinensis with 2n = 65 formed 32 bivalents and one univalent in microspore mother cells. Meiosis of both cytotypes was almost regular and yielded microspores of normal appearance. In the heptaploid (2n = 77) of I. japonica, a configuration of 22 bivalents and 33 univalents was detected in micro- and megaspore mother cells, and various irregularities were observed throughout the meiotic divisions. Therefore, the genomic formula of the heptaploid is symbolized as AABBCDE, and the heptaploid is a sterile [F.sub.1] hybrid between the hexaploid (AABBCC) and the octaploid (AABBDDEE) of I. japonica. Since diploid and even-numbered polyploids regularly formed bivalents and odd-numbered ones displayed irregularities, allopolyploidy should act as a significant speciation mechanism in this genus. Key words: chromosome; hybrid; Isoetes; megasporogenesis; meiosis; microsporogenesis; polyploid; reproductive mode.

Few integrative analyses of the structure of agamospermous plant populations have been conducted. Erigeron compositus occurs in montane western North America and comprises both sexual and agamospermous populations. Sexual E. compositus has previously been characterized as outcrossing and predominantly diploid (2n = 18). Agamic E. compositus is usually hexaploid (2n = 54), though counts herein range from 2n = 36 to 2n = 80. Starch-gel electrophoresis, cytology, and analysis of pollen production were used to evaluate variation within and among agamospermous populations. Fifteen enzyme loci were used to identify 24 unique multilocus genotypes in seven populations, an average of 3.4 genotypes per population. Proportion of distinct genotypes per population sample size (G/N) and measures of genetic diversity (D) and evenness (E) are 0.10, 0.48, and 0.61, respectively, which indicate that E. compositus maintains levels of diversity similar to other agamospermous taxa. Most agamospermous populations are mosaics comprising groups of genetically distinct individuals that are frequently distinguished by cytotype and capacity for pollen production. The geographical and ecological separation of sexual and agamospermous populations make it unlikely that gene flow from sexual populations is a direct source of genetic variation in agamospermous populations. Instead, crossing between genetically distinct facultative agamosperms probably accounts for most variation. Genetic and morphological evidence document one such putative crossing event. Agamospermous E. compositus is very similar genetically to sexual E. compositus. Allozyme analysis further shows that genetic variation in agamospermous populations is partitioned among a few highly heterozygous genotypes, whereas sexual populations maintain numerous genotypes of relatively low heterozygosity. Key words: agamospermy; Asteraceae; Erigeron compositus; isozyme analysis; polyploidy; population structure.

Ribulose-biphosphate carboxylase gene sequences provide data on the evolutionary lineages of leptosporangiate ferns. The data reveal the close association between Salvinia and Marsilea water ferns and the monophyletic characteristics of the fern trees. The polypodioids are related to the gleichenioids and similar to indusiate and exindusiate ferns.

Gene studies of imperfect yeast Candida albicans reveal that both types of polyploidization pld mutants Pld+ and Pld- exhibit increased level of chromosome missegregation. Production of high ploidy cells in C. albicans is due to delay in G2M Phase of the cell cycle influenced by genetic factors which also cause chromosomal tris segregation. Chromosome instability in both Pld and Pldts strains is caused by segregation of auxotrophic markers including ade 1.

An analysis of genetic variation in the third intron (C) of the growth hormone genes of salmonid fishes, coho salmon, involved application of the polymerase chain reaction. A variable number of copies of 31-nt repeat, not evident for GH-1 of the intimately associated chinook salmon and rainbow trout, is responsible for a polymorphism in the length of intron C.

This study was undertaken in order to determine the population structure in a tropical, geographically isolated liverwort, Marchantia globosa Brid. ex Web., a thallose species endemic to the Mascarenes and Comoro Islands. A survey of numerous populations on Reunion showed M. globosa to be ecologically tolerant and morphologically quite variable. The morphological differences between populations could only be explained by a size effect, due principally to altitude. Neither cytological nor electrophoretic analyses revealed any genetic basis for distinguishing subpopulations. In spite of an apparently high reproductive effort, sexual structures being produced abundantly, few spores reach maturity. No electrophoretically detectable genetic polymorphism was found. Morphological variation appears to result from phenotypic plasticity.

A study was conducted to analyze the identity of Azotobacter vinelandii as a polyploid bacterium. Earlier findings based on chromosome size and DNA content per cell indicated such an identity for Azotobacter vinelandii. However, genetic operations performed on it indicate noncompliance with the nature of polyploid bacteria. These operations include chromosomal lac fusions and delay analysis involving mutations. Results of these tests show that Azotobacter vinelandii is not a polyploid bacterium.

We define a new genetic identity measure that is especially well suited for asexual polyploid species as it circumvents erros in the estimation of gene frequencies. It also can be applied to sexuals allowing the study of phylogenetic relationships in species complexes consisting of sexuals and asexuals of different ploidy levels. The measure groups genotypes into classes dependent on homozygosity vs heterozygosity and the number of ancestral allele types vs the number of presumed new mutations. Its value is related to evolutionary time since divergence. The application of the method is illustrated by using electrophoretic data on the species group Solenobia triquetrella (Lepidoptera: Psychidae). A high similarity of estimated relationships among the proposed as well as other genetic identity measures is shown in the case of diploid sexual and asexual races of this species group. The phylogenetic relationships within the group are reanalyzed and monophyletic vs polyphyletic origin of parthenogenesis in this species complex is discussed. The genetic identity values found by the proposed procedure are explained by a polyphyletic origin of parthonogenesis, though a monophyletic origin of parthenogenesis in a broader sense cannot be excluded. The explanation of the phylogenetic relationships is based on the assumption of hybridization between related species and the extinction of one ancestral species. Furthermore, the genetic diversity is compared among sexual and parthenogenetic races of the species. Key words.--Genetic identity, genetic diversity, origin of parthenogenesis, polyphyly, polyploidy, phylogeny.

The genus Triticum includes several polypoid species that arose due to hybridization between two or more diploid species. Section Sitopsis is comprised of five diploid species given the genome designation S. Four polypoid species are recognized that contain an S or S-derived genome. We have used two repetitive DNA sequences found primarily in the S genomes of Triticum to determine the likely diploid progenitors of the polyploid species. Comparison of restriction fragments that hybridize to probes for these sequences suggests that T. speltoides is distinct from other members of section Sitopsis (i.e., T. longissimum, T. bicorne, T. Searsii, and T. sharonense). The S-derived genome of T. aestivum is more closely related to T. speltoides than to the other Sitopsis diploids. The restriction fragment pattern of T. syriacum are identical to the group of diploids represented by T. longissimu, T. bicorne, T. searsii, and T. sharonense. Our results are compatible with previous molecular and biochemical data regarding relationships among Triticum species containing an S or S-derived genome.

The uses of a variety of phylogenetic approaches to unravel origins and understand reticulation history in a diploid-polyploid complex of black-fruited Crataegus are demonstrated. The findings provide experimental evidence for different pathways of polyploid formation that are all likely to occur within natural populations and the allopatric establishment of neopolyploids subsequent to their formation.

Several analyses of the asexual Eucypris virens ostracods are conducted to explain the various effects of the ploidy, as well as asexual reproduction on the success of asexual lineages. The results demonstrate the presence of highly differentiated diploid sexual populations.

The genetic control of variation in leaf trichome density in a diploid A genome cotton is examined. It further discussed its relationship to trichome and fiber-related genes in tetraploids.

A number of parthenogenetic organisms appear to have survived for extended periods in spite of the clonal inheritance factor that usually increases the risk of the extinction of the clonal population. One reason for this could be that parthenogens sometimes reproduce through sex-like processes and to better understand the mechanism involved a study of the sex-like processes in the planarian flatworm 'Schmidtea (Dugesia) polychroa was undertaken.

Eragrostis tef (Zucc.) Trotter (Poaceae) is an allotetraploid cereal crop cultivated primarily in Ethiopia and Eritrea. Of the approximately 350 species in Eragrostis, a total of thirteen potential diploid and polyploid progenitors have been proposed to be the sources of tef's genome, but rigorous tests of these competing hypotheses have not been performed. We are using sequence data from a 1250 bp region of the waxy locus (granule-bound starch synthase; GBSSI), a low-copy nuclear gene, to test the hypotheses of tef's origins. We have amplified 2 partial and 4 complete exons and 5 introns from this locus, and have sampled homoeologous copies of the gene in the polyploid taxa. Preliminary results from cladistic analyses of waxy sequences support the widely held notion that tef is a domesticate of E. pilosa, a widespread and morphologically similar allotetraploid.

This paper explores the efforts of two Berkeley geneticists E. B. Babcock and G. Ledyard Stebbins to understand the genetic basis of evolutionary change in the complex plant genus, Crepis. The paper introduces us to an important research project that has been neglected by historians. Begun in the nineteen-teens, the project on the genetics and systematics of the genus Crepis (and its relatives) was meant to emulate the success of the Drosophila genetics research program that was orchestrated by Thomas Hunt Morgan at Columbia University and later at the California Institute of Technology. The project was in fact Babcock's dream of finding an easily tractable model organism that would integrate genetics with systematics, but that would also resolve some persistent problems in plant genetics that remained unexplained after Mendel. The paper traces the history of the articulation of the polyploid complex and ends with the publication of Babcocks' Genus Crepis in 1947. The paper additionally locates Babcock and Stebbins in the agricultural context of the University of California, Berkeley, and Babcock's pioneering efforts to create one of the first departments of genetics in the United States.

Biologists tend to think of the normal ploidy (number of complete chromosome sets) of cells as either diploid (2n) or haploid (n). Yet examples of polyploidy (more than two sets [...]