Isozyme expression in F1 hybrids between carp and goldfish

Interspecific genetic differences in malate dehydrogenase (MDH), lactate dehydrogenase (LDH), superoxide dismutase (SOD), and esterase (EST) isozymes in carp (Cyprinus carpio) and goldfish (Carassius auratus) were used to examine the allelic expressions in the hybrid between these species. A unique liver SOD and muscle LDH phenotype unambiguously identifies all presumed hybrid individuals. There was no evidence of F₂ or backcross phenotypes in hybrid individuals. Liver MDH and EST phenotypes in hybrids show a preferential expression of goldfish isozymes. Variation in the levels of carp liver MDH isozymes may result from the polymorphism of a regulatory mutation affecting isozyme expression, leading to gene silencing after duplication.This work was supported through NSERC (Canada) grants to James P. Bogart and John F. Leatherland.     

Cytogenetic studies of the F1 hybrids of Capsicum annuum with C. chinense and C. baccatum

Summary Partially sterile interspecific hybrids were obtained between C. annuum var. cerasiformis and C. chinense var. mishme (H₁), and C. annuum var. cerasiformis and C. baccatum var. pendulum (H₂). Morphologically the F₁ hybrids were intermediate between the corresponding parents. Meiosis was irregular in the two F₁ hybrids. Cytological analysis of the two F₁ hybrids revealed that the genome of C. annuum differs from C. chinense by two translocations and some minor structural alterations and from C. baccatum by two translocations, a single inversion and some minor structural alterations. Isolation barriers such as hybrid inviability, weakness and hybrid breakdown in the H₁ hybrid and, inaddition, desynapsis in the H₂, were operative in these taxa. The differences between the present findings and those reported earlier on the two F₁hybrids were attributed to differences in the genetic architecture of the taxa employed in hybridization.     

Chromosomal rearrangements directly cause underdominant F1 pollen sterility in Mimulus lewisii–Mimulus cardinalis hybrids

Chromosomal rearrangements can contribute to the evolution of postzygotic reproductive isolation directly, by disrupting meiosis in F₁ hybrids, or indirectly, by suppressing recombination among genic incompatibilities. Because direct effects of rearrangements on fertility imply fitness costs during their spread, understanding the mechanism of F₁ hybrid sterility is integral to reconstructing the role(s) of rearrangements in speciation. In hybrids between monkeyflowers Mimulus cardinalis and Mimulus lewisii, rearrangements contain all quantitative trait loci (QTLs) for both premating barriers and pollen sterility, suggesting that they may have facilitated speciation in this model system. We used artificial chromosome doubling and comparative mapping to test whether heterozygous rearrangements directly cause underdominant male sterility in M. lewisii–M. cardinalis hybrids. Consistent with a direct chromosomal basis for hybrid sterility, synthetic tetraploid F₁s showed highly restored fertility (83.4% pollen fertility) relative to diploids F₁s (36.0%). Additional mapping with Mimulus parishii–M. cardinalis and M. parishii–M. lewisii hybrids demonstrated that underdominant male sterility is caused by one M. lewisii specific and one M. cardinalis specific reciprocal translocation, but that inversions had no direct effects on fertility. We discuss the importance of translocations as causes of reproductive isolation, and consider models for how underdominant rearrangements spread and fix despite intrinsic fitness costs.     

Inheritance of Oryza sativa endornavirus in F1 and F2 hybrids between japonica and indica rice

We have found a 14 kbp double-stranded RNA (dsRNA) in many cultivars of japonica rice (Oryza sativa L.) but not in any cultivars of indica rice. This dsRNA is an RNA replicon with plasmid-like properties and is proposed to be a novel dsRNA virus, Oryza sativa endornavirus (OSV). Reciprocal crosses between the OSV-carrier japonica variety (Nipponbare) and the OSV-free indica variety (IR 26 or Kasalath) were performed to investigate whether OSV can be transmitted to F1 hybrids. When IR 26 and Nipponbare were used, efficient transmission of OSV from ova (93%) and pollen (89%) was observed. When Kasalath and Nipponbare were used, the OSV transmission efficiency to F1 progeny was 68% from ova and 20% from pollen. The transmission of OSV to F2 progeny plants was also complicated, showing non-Mendelian inheritance. These results suggest that the dsRNA replicon (OSV) is unstable in indica rice plants.     

Chromosomal abnormalities in hypoprolific boars

Four new chromosomal rearrangements are reported in the domestic pig: 3 reciprocal translocations, rcp(4;12)(p13;q13) in a crossbred boar, rcp(1;7)(q17;q26) in a Large White purebred boar, rcp(1;6)(q17;q35) in a purebred synthetic paternal line boar, and a pericentric inversion inv(2)(p13q11) in a crossbred boar. The 1/7 reciprocal translocation and the pericentric inversion were detected in animals that had sired small litters. The effect of the 1/7 translocation was accurately determined: -4.5 piglets born per litter, i.e. -36%. Both the 1/6 and 1/7 reciprocal translocations were of maternal origin. All the chromosomal rearrangements were highlighted using GTG and/or RBG banding techniques. Chromosome painting experiments were also carried out to confirm the proposed hypotheses for the three reciprocal translocations.     

Cytogenetics of F1 hybrids between Cajanus and Atylosia species and its phylogenetic implications

Summary Cytogenetic relationships between two cultivars of Cajanus cajan and six species of Atylosia were investigated. Of the 12 cross combinations obtained, only seven could be studied. Meiotic chromosome pairing, pollen and ovule fertility in parental species and four F1 hybrids were near normal. Some meiotic abnormalities were observed in the Fls: A. lineata x A. scarabaeoides, A. scarabaeoides x A. sericea and C. cajan (UPAS 120) x A. trinervia, indicating varying degrees of chromosomal and genic differences between these species. These observations suggested that A. cajanifolia is the closest wild relative of C. cajan, followed by A. scarabaeoides, A. albicans and A. trinervia. Among the Atylosia species, A. sericea was closer to A. scarabaeoides than to A. lineata.Botanist, Genetic Resources Unit, ICRISAT, Patancheru-502 324, IndiaRegional Plant Production and Protection Officer, FAO, RAPA, Bangkok-2, Thailand     

Fitness of F1 hybrids between 10 maternal wild soybean populations and transgenic soybean

Transgenic Research - The releasing of transgenic soybeans (Glycine max (L.) Merr.) into farming systems raises concerns that transgenes might escape from the soybeans via pollen into...     

Comparative proteome analysis of cellular proteins extracted from highly virulent Francisella tularensis ssp. tularensis and less virulent F. tularensis ssp. holarctica and F. tularensis ssp. mediaasiatica

Francisella tularensis is the causative agent of the zoonotic disease tularemia. Four subspecies of this pathogen, namely ssp. tularensis, mediaasiatica, holarctica, and novicida are spread throughout the northern hemisphere. Although there are marked variations in their virulence to mammals, the subspecies are difficult to identify as they are closely genetically related. We carried out the comparative proteome analysis of cellular extracts from isolates representing the highly virulent subspecies tularensis, and the less virulent subspecies mediaasiatica and holarctica in order to identify new diagnostic markers and putative factors of virulence. We identified 27 protein spots that were either specifically present or at significantly higher abundance in ssp. tularensis strains, 22 proteins in ssp. mediaasiatica strains, and 26 proteins in ssp. holarctica strains. Subspecies tularensis-specific proteins might represent putative virulence factors. Of 27 identified tularensis-specific spots 17 represented charge and mass variants of proteins occurring in other subspecies, 7 spots were found to be present at higher abundance, and 3 spots were specifically present in tularensis strains. Amongst them, PilP protein, as a component necessary for the biogenesis of the type IV pilus, virulence and adhesion factor for many human pathogen, was identified. Furthermore, the identification of additional 27 proteins common for ssp. tularensis and mediaasiatica, and 19 proteins shared by ssp. mediaasiatica and holarctica documented apparent closer genetic similarity between ssp. tularensis and mediaasiatica.     

Chromosomal and molecular rearrangements in somatic hybrids between tetraploid Medicago sativa and diploid Medicago falcata

The aim of this study was to produce somatic hybrids between tetraploid (2n=4x=32) M. sativa and diploid (2n=2x=16) M. ?falcata and analyse their genomic structure. Protoplasts from genotypes selected for regeneration ability from the cultivar Rangelander of M. sativa and Wisfal-1 of M. falcata were electrofused. Seven somatic hybrid calli were produced and one of them regenerated plants. The hybrid nature of these plants and their genetic composition were assessed with morphological, cytological, and molecular analyses. The resulting plants were hyper-aneuploid (2n=33) and contained one extra long chromosome, indicating that a translocation had taken place. The presence of both types of parental sequences in the RAPDs analysis confirmed the true hybrid nature of the plants. Rearrangements within the parental genomes and the presence of somaclonal variation among hybrid plants were observed through an RFLP analysis of the nucleolar organizing region (NOR). The possible causes for the gross genomic alterations, and the suitability of this method for transferring useful agronomic traits from wild species to cultivated alfalfa, are discussed.     

Inheritance of RAPDs in F1 hybrids of corn

Summary Random amplified polymorphic DNA (RAPD) markers were analyzed in materials from a partial diallel, including 16 corn F₁ hybrids (with five reciprocals) and their five parental inbreds. Using 21 primers, we scored a total of 140 different fragments for their presence/absence and intensity variation, where appropriate. When all 21 genotypes were taken into consideration, 20.7% of these fragments were nonpolymorphic, 37.1% were unambiguously polymorphic, and 42.1% were quantitatively polymorphic. Unambiguous polymorphisms were distinguished by the simple presence or absence of a specific fragment in the inbred genotypes, whereas quantitative polymorphisms exhibited a variation in the intensity of a fragment. Of the F₁ patterns, 95.2% of the unambiguously polymorphic situations could be interpreted genetically by assuming complete dominance of the presence of the parental fragment, while 3.2% of the F₁ patterns exhibited a fragment intensity that was intermediate between the two parental patterns (partial dominance). For quantitative polymorphisms, values of 88.1% for complete dominance and 5.0% for partial dominance were obtained. The results suggest that specific types of errors can be detected in RAPD analysis, that uniparental inheritance is not common, and that RAPD analysis might be more prudently used for some applications than for others.     

Chromosomal abnormalities and the morphology of mouse sperm heads.

In the mouse, numerous mutagens, teratogens and carcinogens have been shown to induce marked elevations in the fraction of sperm with head shape abnormalities. Since carcinogens and teratogens may act by causing genetic damage, a likely explanation of these results is that the sperm abnormalities are also caused by genetic damage. There are two more or less distinct classes of genetic damage, chromosomal aberrations and point mutations. In this paper, we provide evidence, that in general, chromosomal aberrations are not responsible for causing abnormally shaped sperm. Chromosomal aberrations could have caused abnormal sperm morphology in a number of ways. One possibility was that the mere presence of a translocated chromosome within the germ cell led to the malformation of the sperm head. A second possibility was that chromosomal imbalance, i.e., aneuploidy, duplications or deficiencies, within the spermatid or haploid cells caused abnormalities in shape. We tested these hypotheses by measuring the level of abnormally shaped sperm in mice homozygous and heterozygous for 24 various reciprocal and Robertsonian translocations. The diploid cells of these mice are known to be chromosomally balanced, containing translocated chromosomes. A predictable proportion of their gametes are, however, chromosomally unbalanced and carry translocated chromosomes. It was found that the levels of sperm abnormalities in these mice were convincingly unrelated to the levels predicted by any of the above hypotheses. Based on these results it seems that sperm abnormalities in mice are not due to the mere presence of translocated chromosomes in germ cells and also not due to chromosomal aneuploidy or duplication-deficiencies of chromosomal segments in the spermatid during development of the sperm.     

Population Structure of Morphological Traits in Clarkia Dudleyana I. Comparison of F(st) between Allozymes and Morphological Traits

The X-linked white gene when transposed to autosomes retains only partial dosage compensation. One copy of the gene in males expresses more than one copy but less than two copies in females. When inserted in ectopic X chromosome sites, the mini-white gene of the CaspeR vector can be fully dosage compensated and can even achieve hyperdosage compensation, meaning that one copy in males gives more expression than two copies in females. As sequences are removed gradually from the 5' end of the gene, we observe a progressive transition from hyperdosage compensation to full dosage compensation to partial dosage compensation. When the deletion reaches -17, the gene can no longer dosage compensate fully even on the X chromosome. A deletion reaching +173, 4 bp preceeding the AUG initiation codon, further reduces dosage compensation both on the X chromosome and on autosomes. This truncated gene can still partially dosage compensate on autosomes, indicating the presence of dosage compensation determinants in the protein coding region. We conclude that full dosage compensation requires an X chromosome environment and that the white gene contains multiple dosage-compensation determinants, some near the promoter and some in the coding region.     

Chromosomal and embryological analyses in sexual x apomictic hybrids ofPanicum maximum Jacq.

Summary Cytological analyses in series of crosses between 7 sexual pistillate and 8 apomictic staminate parents of speciesPanicum maximum (Gramineae) are reported. Although these 15 progenitors were tetraploid (2n = 32), 2 dihaploids (2n = 16), 45 hexaploids (2n = 48) and 5 octoploids (2n = 64) were observed among 333 progeny plants. The role of unreduced gametes as the originators of polyploidy is discussed in relation to the so-called elements of apomixis. The 2 dihaploids appeared to be sexual while the hexaploids and octoploids were all apomictic. At the tetraploid level sexual and apomictic hybrids segregated in a ratio close to 11. These results were then compared to those already obtained from studies on other tropical grasses and indicate a simple genetic determinism for gametophytic apomixis.     

A method for increased plant regeneration from immature F1 and BC1 embryos of Cucurbita maxima Duch. x C. pepo L. hybrids

Plants have been regenerated from abnormal embryos with spongy cotyledons and albino sectors, derived from Cucurbita maxima and C. pepo F₁ and BC₁ hybrids. Shoot regeneration was induced directly from the cotyledons without an intervening callus phase on the medium without hormones. On the rooting medium, shoots continued to proliferate, which allowed for further multiplication in vitro. The number of plants obtained varied with genotype and ranged up to 65 plants per embryo.     

Polymorphic Chromosomal Specificity of Centromere Satellite Families in Arabidopsis halleri ssp. gemmifera

The chromosomal localizations of repetitive DNA clusters (ribosomal DNA and centromere satellites) were analyzed by fluorescent in situ hybridization in five strains of Arabidopsis halleri ssp. gemmifera. All five A. gemmifera strains have three chromosome pairs with 45S (5.8S-16S-26S) rDNA loci, and one pair with both 5S and 45S rDNA loci. These localizations are different from that of A. thaliana. Very unusually, there are three families of centromeric satellite DNAs (pAa, pAge1, and pAge2), and they showed polymorphism among the five strains studied. Overall, we found four different centromere satellite compositions. A plant from Fumuro was heterozygous for the chromosome specificities of centromere satellite families, possibly due to a reciprocal translocation involving centromere regions. Changes of centromeric satellite repeats appear to be rapid and frequent events in the history of A. gemmifera, and seem to occur by exchanging clusters as units.     

Asexual and sexual hybrids between Fundulus diaphanus and F. heteroclitus in the Canadian Atlantic region

Levels and origins of clonal diversity in asexual hybrid animals are critical to understanding how they can coexist with their sexual progenitor species. In this study, asexual gynogenetic hybrids between Fundulus diaphanus and Fundulus heteroclitus known from two sites in Nova Scotia (Canada) were characterized using discriminant morphological traits, eight microsatellite loci, and mitochondrial DNA. Fifteen clonal genotypes were uncovered, all bearing the same F. diaphanus maternal haplotye. Each site harboured a different dominant clone along with several rarer clones that all appear to be of recent origin. Unexpectedly, highly introgressed sexually reproducing hybrids (0.25 > q > 0.75) were also detected. Sexual hybrids with maternal ascendance in either species were also found at three other sites in the Atlantic region. Based on a single meristic trait (scale counts), it is shown that asexual clones can be significantly more variable than populations of sexual parental species. Also, species are morphologically more alike when living in sympatry, suggesting that introgression may occur via sexual hybrids. Altogether, these results confirm and refine the available knowledge on this hybrid system, and indicate that hybridization is probably a more widespread phenomenon than suspected, with implications for the phenotypic variability of a widely used model species, F. heteroclitus.     

Chromosome identification and nuclear architecture in triticale tritordeum F1 hybrids

In situ hybridization with cloned, repetitive DNA probes andtotal genomic DNA enables the parental origin of all chromosomesto be established in metaphases of triticale tritordeum F¹hybrids (2n=6x=42). Nuclei contain seven chromosomes of Hordeumchilense origin, seven from Secale cereale and 28 of wheat origin.When used as a probe, total genomic rye DNA labelled the ryechromosomes strongly and uniformly along their lengths, withbrighter regions coincident with the terminal heterochromatin.The probe labelled the wheat-origin chromosomes weakly and wasalmost undetectable on the H. chilense-origin chromosomes. Incontrast, under the same conditions, H. chilense DNA hybridizedstrongly to the H. chilense- and, with intermediate strength,to the S. cereale-origin chromosomes, excluding the subtelomericheterochromatin: it hybridized only weakly to the wheat chromosomes,in some experiments revealing characteristic bands on wheatchromosomes. Cloned repetitive DNA probes from rye and H. chilensewere used as probes to identify the linkage groups of all oftheir own-species chromosomes. Analysis of hybridization patternsof various probes to prophase and interphase nuclei indicatedthat there are many non-random features in the localizationof both repetitive DNA and whole chromosomes, although generalpatterns of nuclear organization have yet to emerge. Both theparticular lines used and the techniques developed here arelikely to be valuable for production and characterization ofplant breeding material. Key words: In situ hybridization, triticale, cytogenetics, plant breeding, Hordeum chilense