Cytolegical Studies of Genus Petunia
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1. The tetraploid plant of giant variety of Petunia was selfed. Among 31 plants of the F1 progeny 29 were tetraploid, one 4n-1 and one 4n-3. No significant morphological differences were noticed among them.2. The tetraploid plants of the giant variety and the diploid plants of small variety were crossed reciprocally. Among the populations of F1 progenies two gave a high percent of triploids besides each one plant of heteroploids and a diploid. The third gave no triploid but respectively one plant of 2n, 3n+2 and 4n. Among these three diploid plants, one was completely different from both the parents, while the other two were complete replicas of the diploid parent. The triploid plants showed approximately intermediate characters more or less tending toward the tetraploid parent.3. The triploid progeny was cytologically studied. In the heterotypic metaphase 7 sets of trivalent were not infrequentiy found. Almost all the trivalent configurations possible in auto-triploids were observed excepting one. Besides these the ring of three or triangle, and the multivalents were sometimes met with. These may be interpreted by the segmental interchange hypothesis.4. The 2n×4n crossing gave only the diploid progeny in one Gase. These progeny exhibited exactly the same characters morphologically as well as physiologically as the diploid parent. Another mating resulted in three tetraploids and one 4n-1 plant.5. The triploid hybrids selfed gave 26, 27, 28 and 29 chromosome plants in the F, progeny among which 27 chromosome plants were of the highest fequency. The majority of these progenies had one or two fragments of chromosomes. A trabant derived from the diploid ancestor is identified at one end of one of the chromosomes.6. The triploid hybrid was back crossed to the diploid parent. Three plants were obtained with the somatic number respectively of 19, 20 and 21. This shows that the gametes of the triploid with the chromosome numbers of 12, 13 and 14 function.7. The tetraploid-triploid crossings gave the F1 progenies of 24, 26, 27, 28 and 29 chromosomes with respective frequencies of 1, 6, 17 and 29.8. The reciprocals of the above crossings gave one 29 chromosome plant and twenty 28 chromosome plants.9. The appearance of diploid progenies in the crossings between 2n and 4n plants may be explained by the diploid parthenogenesis.10. As to the appearance of diploid progenies in 4n×2n crossings, two different Gases must be distinguished: (1) diploid parthenogenesis and (2) merogony. Both of these are supposed to occur.11. The occurrence of tetraploid plants among the F1 progeny of 4n×2n crossings probably was induced by the fertilization of an egg nucleus by a generative nucleus with double number of chromosomes.12. The tetraploid and triploid plants of Petunia must be autotetraploid and auto-triploid.Keywords:
Petunia
Chromosome pairing
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The potential for gene exchange between species with different ploidy levels has long been recognized, but only a few studies have tested this hypothesis in situ and most of them focused on not more than two co-occurring species. In this study, we examined hybridization patterns in two sites containing three species of the genus Dactylorhiza (diploid D. incarnata and D. fuchsii and their allotetraploid derivative D. praetermissa). To compare the strength of reproductive barriers between diploid species, and between diploid and tetraploid species, crossing experiments were combined with morphometric and molecular analyses using amplified fragment length polymorphism markers, whereas flow cytometric analyses were used to verify the hybrid origin of putative hybrids. In both sites, extensive hybridization was observed, indicating that gene flow between species is possible within the investigated populations. Bayesian assignment analyses indicated that the majority of hybrids were F1 hybrids, but in some cases triple hybrids (hybrids with three species as parents) were observed, suggesting secondary gene flow. Crossing experiments showed that only crosses between pure species yielded a high percentage of viable seeds. When hybrids were involved as either pollen-receptor or pollen-donor, almost no viable seeds were formed, indicating strong post-zygotic reproductive isolation and high sterility. Strong post-mating reproductive barriers prevent local breakdown of species boundaries in Dactylorhiza despite frequent hybridization between parental species. However, the presence of triple hybrids indicates that in some cases hybridization may extend the F1 generation.
Reproductive isolation
Orchidaceae
Polyploid
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Two species of loach, the mud loach (Misgurnus mizolepis Günther) and the cyprinid loach (M. anguillicaudatus Cantor), are commercially important in Korea both for food and ceremonial purposes. The mud loach has superior potential for aquaculture in terms of growth, whereas the cyprinid loach has a more desirable body shape and colour. This study was conducted to produce reciprocal diploid and triploid hybrids and to evaluate their potential benefits in culture by examining growth performance, morphometrics and gonad development. Reciprocal diploid and triploid hybridization was performed by artificial insemination without or with the induction of triploidy. The successful formation of diploid or triploid karyogamy was verified by flow cytometric analysis. Body weights of induced reciprocal diploid hybrids were intermediate between those of the two parental species, i.e. hybrids were heavier than cyprinid loach but lighter than mud loach. In contrast, the growth performance of triploid hybrids was similar to that of their corresponding maternal parents. Diploid hybrids showed intermediate morphometric traits between the two species; however, the body proportions of triploid hybrids were more similar to those of the maternal species than the paternal species. Histological analyses indicated that reciprocal diploid hybrids of both sexes were able to reach maturity, as evidenced by the presence of mature oocytes or spermatozoa in the gonad tissues. However, triploid hybrids showed stringent sterility at the gonadic level; the sizes of ovaries and testes were much smaller, and gonad development was abnormal and significantly retarded.
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Cobitidae
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Total cellular DNA content, determined by a colorimetric method, was used as an index of ploidy in Candida albicans. Mononucleate hybrids were formed by fusion of spheroplasts derived from diploid parent strains. Five hybrids, of six studied, were taken to be tetraploid on the basis of estimated DNA content. One hybrid was taken to be hexaploid or near-hexaploid. Selection for increased resistance to 5-fluorocytosine in the hybrids, which were heterozygous for resistance, resulted in isolation of variants which were of lower ploidy than the hybrids from which they originated. Variants were obtained which corresponded (in measured DNA content) to aneuploid, triploid, and diploid states. These results may form the basis of a cyclic parasexual system (2n X 2n----4n----2n) for genetic analysis of this asexual species.
Spheroplast
Genetic Analysis
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The aim of the present study was to produce Acipenser baeri× (Huso huso×Acipenser ruthenus) hybrids in a diploid and triploid state and to study their viability in comparison with the A. baeri from the fish farm stock. A heat shock (37°C) in the 18th minute after fertilization was applied to induce triploidy. The survival rate and the ploidy level of the hybrids obtained were studied. The mortality of triploid hybrids was approximately twice as high as the mortality of diploid hybrids. No significant difference in the survival rate between Siberian sturgeon and their diploid hybrid with bester was noted. Cytogenetic analysis was performed by preparing chromosomes from the gill epithelium. The results showed that all studied fish from the heat-shocked group were triploid.
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