Reduction In Chromosome Number Research Articles

Fast Diploidization in Close Mesopolyploid Relatives ofArabidopsis

Mesopolyploid whole-genome duplication (WGD) was revealed in the ancestry of Australian Brassicaceae species with diploid-like chromosome numbers (n = 4 to 6). Multicolor comparative chromosome painting was used to reconstruct complete cytogenetic maps of the cryptic ancient polyploids. Cytogenetic analysis showed that the karyotype of the Australian Camelineae species descended from the eight ancestral chromosomes (n = 8) through allopolyploid WGD followed by the extensive reduction of chromosome number. Nuclear and maternal gene phylogenies corroborated the hybrid origin of the mesotetraploid ancestor and suggest that the hybridization event occurred approximately 6 to 9 million years ago. The four, five, and six fusion chromosome pairs of the analyzed close relatives of Arabidopsis thaliana represent complex mosaics of duplicated ancestral genomic blocks reshuffled by numerous chromosome rearrangements. Unequal reciprocal translocations with or without preceeding pericentric inversions and purported end-to-end chromosome fusions accompanied by inactivation and/or loss of centromeres are hypothesized to be the main pathways for the observed chromosome number reduction. Our results underline the significance of multiple rounds of WGD in the angiosperm genome evolution and demonstrate that chromosome number per se is not a reliable indicator of ploidy level.

Chromosome Evolution in African Cichlid Fish: Contributions from the Physical Mapping of Repeated DNAs

Cichlid fishes have been the subject of increasing scientific interest because of their rapid adaptive radiation that has led to extensive ecological diversity and because of their enormous importance to tropical and subtropical aquaculture. To further understanding of chromosome evolution among cichlid species, we have comparatively mapped the SATA satellite DNA, the transposable element ROn-1, and repeated sequences in the bacterial artificial chromosome clone BAC-C4E09 on the chromosomes of a range of African species of Cichlidae, using fluorescence in situ hybridization. The SATA satellite DNA was mapped in almost all the centromeres of all tilapiine and haplochromine species studied. The maintenance and centromeric distribution of the SATA satellite DNA in African cichlids suggest that this sequence plays an important role in the organization and function of the centromere in these species. Furthermore, analysis of SATA element distribution clarifies that chromosome fusions occurred independently in Oreochromis and Tilapia genera, and led to the reduced chromosome number detected in O. karongae and T. mariae. The comparative chromosome mapping of the ROn-1 SINE-like element and BAC-C4E09 shows that the repeated sequences have been maintained among tilapiine, haplochromine and hemichromine fishes and has demonstrated the homology of the largest chromosomes among these groups. Furthermore, the mapping of ROn-1 suggested that different chromosomal rearrangements could have occurred in the origin of the largest chromosome pairs of tilapiines and non-tilapiines.

Genomic plasticity of the human fungal pathogen Candida albicans.

The genomic plasticity of Candida albicans, a commensal and common opportunistic fungal pathogen, continues to reveal unexpected surprises. Once thought to be asexual, we now know that the organism can generate genetic diversity through several mechanisms, including mating between cells of the opposite or of the same mating type and by a parasexual reduction in chromosome number that can be accompanied by recombination events (2, 12, 14, 53, 77, 115). In addition, dramatic genome changes can appear quite rapidly in mitotic cells propagated in vitro as well as in vivo. The detection of aneuploidy in other fungal pathogens isolated directly from patients (145) and from environmental samples (71) suggests that variations in chromosome organization and copy number are a common mechanism used by pathogenic fungi to rapidly generate diversity in response to stressful growth conditions, including, but not limited to, antifungal drug exposure. Since cancer cells often become polyploid and/or aneuploid, some of the lessons learned from studies of genome plasticity in C. albicans may provide important insights into how these processes occur in higher-eukaryotic cells exposed to stresses such as anticancer drugs.

High-throughput knockout screen in Schizosaccharomyces pombe identifies a novel gene required for efficient homolog disjunction during meiosis I

Meiosis is the process which produces haploid gametes from diploid precursor cells. This reduction of chromosome number is achieved by two successive divisions. Whereas homologs segregate during meiosis I, sister chromatids segregate during meiosis II. To identify novel proteins required for proper segregation of chromosomes during meiosis, we applied a high-throughput knockout technique to delete 87 S. pombe genes whose expression is upregulated during meiosis and analyzed the mutant phenotypes. Using this approach, we identified a new protein, Dil1, which is required to prevent meiosis I homolog non-disjunction. We show that Dil1 acts in the dynein pathway to promote oscillatory nuclear movement during meiosis.

Chromosome number evolution in Hymenophyllum (Hymenophyllaceae), with special reference to the subgenus Hymenophyllum

With about 100 species distributed worldwide, Hymenophyllum subg. Hymenophyllum is the largest subgenus of filmy ferns. It also displays morphological disparity and extreme chromosome numbers variation, with n=11, 12, 13, 14, 18, 21, 22, 26, 28, and 34. We use DNA sequences from the genes rbcL, part of accD, rps4, and the intergenic spacers rbcL-accD, rps4-trnS, and trnG-trnR to infer relationships within Hymenophyllum, with a focus on this subgenus. In the subgenus Hymenophyllum, two main clades are retrieved together with several minor clades whose placement within the subgenus remains ambiguous. We then investigate the evolution of chromosome numbers in the genus and the subgenus, using a maximum likelihood approach taking into account phylogenetic uncertainty. We provide evidence that Hymenophyllum experienced descending aneuploidy during its evolutionary history, especially within the subgenus Hymenophyllum. Reduction in chromosome numbers is particularly extreme in one clade of the subgenus, with the lowest number reported for homosporous ferns. In addition, this group of species displays a high instability in its chromosome number. Both the reduction and the instability in chromosome number may coincide with the distribution of these species in either temperate areas or at high elevations.

Pathologic mitoses and pathology of mitosis in tumorigenesis.

The gist of my hypothesis (.. is) a certain abnormal chromatin constitution. Each process, which brings about this chromatin constitution, would result in the origin of a malignant tumour. Certainly, I consider irregularities with mitosis as the normal mode of the origin of an incorrectly assembled nucleus. This statement by Boveri (1914) has considered earlier observations of asymmetric divisions in human cancers (Hansemann, 1890). The hypothesis is based on the understanding of mitosis as an equational bipartition of the hereditary substance (Flemming, 1879; Roux, 1883). Latest since it was known that genes are located on chromosomes (Sturtevant, 1913), their balanced transport in anaphase appeared as a condition of correct somatic proliferation. True mitoses guarantee the constancy of terminally differentiated tissues. Politzer (1934) has performed X-ray experiments to investigate abnormal karyokinesis with regard to anomalous chromatin condensation, chromosome breakage, spindle malformation, and failure in cytokinesis. On the basis of light microscopy, further significant progress in understanding the pathology of mitosis was not possible. Tumour cases with reduced chromosome numbers seduced to the idea that mitotic activity is rather under cytoplasmic than under nuclear control (Koller, 1947).

Phylogeny of Chamaecrista Moench (Leguminosae­Caesalpinioideae) based on nuclear and chloroplast DNA regions

AbstractChamaecrista Moench is a genus of caesalpinioid legumes with about 330 species mostly from the New World. The phylogeny of the genus was studied using sequence data from nuclear ITS and plastid trnL­F DNA spacers, representing all six sections of Chamaecrista. Separate and combined analyses recovered the same major clades with high bootstrap and posterior probabilities support, except for the subclades of representatives of sections Caliciopsis, Chamaecrista, and Xerocalyx. The monophyly of Chamaecrista was highly supported in all analyses. Sections Apoucouita and Xerocalyx were supported as monophyletic, sect. Absus was paraphyletic and subsect. Baseophyllum was resolved more closely related to species of sections Chamaecrista, Caliciopsis, and Xerocalyx than to subsect. Absus. The monotypic section Grimaldia was embedded within subsect. Absus. Section Chamaecrista was paraphyletic with respect to sections Caliciopsis and Xerocalyx. Our analyses suggest that the diversification patterns in Chamaecrista occurred through an initial shift from rainforest trees to a more diverse clade of savannah shrubs. Within the latter group, two main subclades were recovered: (1) a planaltine and high­mountain clade characterized by absence of extrafloral nectaries and the appearance of sticky glandular hairs; and (2) a mostly herbaceous clade with axillary fascicled inflorescences and reduced chromosome numbers. This last group is more diverse in open grassland areas and includes many colonizers of waste ground.

Molecular cytogenetic study of three common Mediterranean limpets, Patella caerulea, P. rustica and P. ulyssiponensis (Archaeogastropoda, Mollusca)

The present paper shows the results of chromosome banding and rDNA-FISH study performed on several specimens of different populations of Patella caerulea, Patella rustica and Patella ulyssiponensis. The taxonomic attribution of specimens was ascertained by the molecular phylogenetic analysis of the mitochondrial 16S rRNA gene. P. caerulea and P. rustica had 2n = 18 chromosomes with first seven of biarmed pairs and the remaining two uniarmed pairs. P. ulyssiponensis had 2n = 16 with all biarmed chromosomes. Ag-NOR loci were on the short arms of the first metacentric pair in the three studied limpets, whereas they showed a different pattern of heterochromatin distribution and composition. A chromosome mosaicism was observed in several P. caerulea specimens, which exhibited an unpaired metacentric element and loss of a telocentric pair. The obtained results suggest that in the genus Patella specific diversification was accompanied by variations in heterochromatin distribution and composition and reduction of chromosome number by Robertsonian centric fusion.

Genome comparisons reveal a dominant mechanism of chromosome number reduction in grasses and accelerated genome evolution in Triticeae

Single-nucleotide polymorphism was used in the construction of an expressed sequence tag map of Aegilops tauschii, the diploid source of the wheat D genome. Comparisons of the map with the rice and sorghum genome sequences revealed 50 inversions and translocations; 2, 8, and 40 were assigned respectively to the rice, sorghum, and Ae. tauschii lineages, showing greatly accelerated genome evolution in the large Triticeae genomes. The reduction of the basic chromosome number from 12 to 7 in the Triticeae has taken place by a process during which an entire chromosome is inserted by its telomeres into a break in the centromeric region of another chromosome. The original centromere-telomere polarity of the chromosome arms is maintained in the new chromosome. An intrachromosomal telomere-telomere fusion resulting in a pericentric translocation of a chromosome segment or an entire arm accompanied or preceded the chromosome insertion in some instances. Insertional dysploidy has been recorded in three grass subfamilies and appears to be the dominant mechanism of basic chromosome number reduction in grasses. A total of 64% and 66% of Ae. tauschii genes were syntenic with sorghum and rice genes, respectively. Synteny was reduced in the vicinity of the termini of modern Ae. tauschii chromosomes but not in the vicinity of the ancient termini embedded in the Ae. tauschii chromosomes, suggesting that the dependence of synteny erosion on gene location along the centromere-telomere axis either evolved recently in the Triticeae phylogenetic lineage or its evolution was recently accelerated.

A preliminary molecular phylogeny of Pennisetum and Cenchrus (Poaceae‐Paniceae) based on the trnL‐F, rpl16 chloroplast markers

ABSTRACTPennisetum (80–140 species) and Cenchrus (16–22 species) are closely related genera of Paniceae, both distributed in tropical and sub‐tropical regions. The distinction between Pennisetum and Cenchrus is not clearly defined, and currently no comprehensive taxonomic treatment is available for either genus. Chloroplast DNA sequence data (rpl16, trnL‐F region) were analyzed to test their monophyly, species relationships, and infrageneric classifications. Phylogenetic analyses of individual genomic regions, and a combined dataset, including indel‐coded information, were performed under parsimony and Bayesian inference. Selected geographical, chromosomal and morphological characters were mapped onto the phylogeny to investigate evolutionary trends. Our results support a monophyletic bristle clade and the close relationship between Pennisetum and Cenchrus. Excluding Pennisetum lanatum, Pennisetum is paraphyletic because Cenchrus is nested within it. Sections Pennisetum and Gymnotrix are polyphyletic. Our molecular phylogenetic results show a close relationship among the domesticated species P. glaucum, P. purpureum, P. squamulatum, P. nervosum, and P. sieberianum, suggesting the potential use of these species in crop improvement. The Pennisetum‐Cenchrus clade shows an independent reduction (x = 5, 7, 8) or duplication (x = 17) of the basic chromosome number from the ancestral x = 9. American Pennisetum and Cenchrus species appear to have originated from Old World species more than once. A core group of American species of Cenchrus with a basic chromosome number of x = 17 and retrorsely barbed bristles could be restricted to Cenchrus s. str.

The stemline idiogram of the MSWBS tumor of the mouse and the problem of centric fusion.

The stemline karyotype of an isoantigenic variant of the mouse sarcoma MSWB is described. In comparison with the original MSWB tumor, which had largely normal mouse karyotype, the variant studied, an ascites tumor called MSWBS, exhibits striking chromosomal changes. Its stemline number is 29 with 10 biarmed and 19 one-armed chromosomes. It was shown by measurements that, in addition to the Robertsonian centric fusion process underlying the reduction in chromosome number, also changes of cryptostructural character have taken place. The karyotype is discussed in relation to other mouse-cell populations with high proportions of biarmed chromosomes, and also in relation to the natural mouse species, the tobacco mouse, which karyotypically differs from the ordinary mouse in much the same way as MSWBS differs from the original MSWB.

Cytogenetic comparison of tree frogs of the genus Aplastodiscus and the Hypsiboas faber group (Anura, Hylidae)

Four species of Aplastodiscus and two species of Hypsiboas were cytogenetically compared. Aplastodiscus perviridis, A. cochranae, H. albomarginaus, and H. faber had 2n = 24 chromosomes, while A. albosignatus and A. leucopygius had 2n = 20 and 2n = 18 chromosomes, respectively. Aplastodiscus perviridis and A. cochranae had identical karyotypes, as indicated by their chromosomal morphology, the location of the nucleolus organizer region (NOR) on chromosome pair 12, and the heterochromatin pattern. The NOR-bearing chromosomes of A. albosignatus and A. leucopygius (pair 9) were very similar in size and morphology (metacentric) when compared to A. perviridis and A. cochranae (pair 12) and to H. faber (pair 11); the NOR of these chromosomes also occurred in the same region, suggesting that these chromosomes are homologous. Although H. albomarginatus differs from the other species with regard to the location of its NOR on pair 2, this species had the same diploid number and a chromosomal morphology similar to that of A. perviridis and A. cochranae. Chromosomal differentiation among the species appears to have occurred by reduction in chromosome number.

Karyotype evolution of giraffes (Giraffa camelopardalis) revealed by cross-species chromosome painting with Chinese muntjac (Muntiacus reevesi) and human (Homo sapiens) paints

Considering the giraffe (Giraffa camelopardalis, GCA, 2n = 30) as a primitive species, its comparative genomic data are critical for our understanding of the karyotype evolution of pecorans. Here, we have established genome-wide chromosomal homologies between giraffe, Chinese muntjac (Muntiacus reevesi, MRE, 2n = 46) and human (Homo sapiens, HSA, 2n = 46) with whole sets of chromosome-specific paints from Chinese muntjac and human, in addition to providing a high-resolution G-banding karyotype of giraffe. Chinese muntjac and human chromosome paints detected 32 and 45 autosomal homologs in the genome of giraffe, respectively. Our results suggest that it would require at least thirteen fissions, six fusions and three intrachromosomal rearrangements to ‘transform’ the 2n = 44 eutherian ancestral karyotype to the 2n = 58 pecoran ancestral karyotype. During giraffe evolution, some ancestral eutherian syntenies (i.e. association of HSA3/21, 4/8, 7/16, 14/15, 16/19 and two forms of 12/22) have been retained, while several derived syntenies (i.e. associations of human homologous segments 2/1, 2/9, 5/19, 4/12/22, 8/9, and 10/20) have been produced. The reduction of chromosome number in giraffe from the 2n = 58 pecoran ancestral karyotype could be primarily attributed to extensive Robertsonian translocations of ancestral chromosomal segments. More complex chromosomal rearrangements (including tandem fusion, centromere repositioning and pericentric inversion) have happened during the evolution of GCA2 and GCA8.

Molecular structures of centromeric heterochromatin and karyotypic evolution in the Siamese crocodile (Crocodylus siamensis) (Crocodylidae, Crocodylia)

Crocodilians have several unique karyotypic features, such as small diploid chromosome numbers (30-42) and the absence of dot-shaped microchromosomes. Of the extant crocodilian species, the Siamese crocodile (Crocodylus siamensis) has no more than 2n = 30, comprising mostly bi-armed chromosomes with large centromeric heterochromatin blocks. To investigate the molecular structures of C-heterochromatin and genomic compartmentalization in the karyotype, characterized by the disappearance of tiny microchromosomes and reduced chromosome number, we performed molecular cloning of centromeric repetitive sequences and chromosome mapping of the 18S-28S rDNA and telomeric (TTAGGG)( n ) sequences. The centromeric heterochromatin was composed mainly of two repetitive sequence families whose characteristics were quite different. Two types of GC-rich CSI-HindIII family sequences, the 305 bp CSI-HindIII-S (G+C content, 61.3%) and 424 bp CSI-HindIII-M (63.1%), were localized to the intensely PI-stained centric regions of all chromosomes, except for chromosome 2 with PI-negative heterochromatin. The 94 bp CSI-DraI (G+C content, 48.9%) was tandem-arrayed satellite DNA and localized to chromosome 2 and four pairs of small-sized chromosomes. The chromosomal size-dependent genomic compartmentalization that is supposedly unique to the Archosauromorpha was probably lost in the crocodilian lineage with the disappearance of microchromosomes followed by the homogenization of centromeric repetitive sequences between chromosomes, except for chromosome 2.

Chromosomal Phylogeny and Karyotype Evolution in x=7 Crucifer Species (Brassicaceae)

Karyotype evolution in species with identical chromosome number but belonging to distinct phylogenetic clades is a long-standing question of plant biology, intractable by conventional cytogenetic techniques. Here, we apply comparative chromosome painting (CCP) to reconstruct karyotype evolution in eight species with x=7 (2n=14, 28) chromosomes from six Brassicaceae tribes. CCP data allowed us to reconstruct an ancestral Proto-Calepineae Karyotype (PCK; n=7) shared by all x=7 species analyzed. The PCK has been preserved in the tribes Calepineae, Conringieae, and Noccaeeae, whereas karyotypes of Eutremeae, Isatideae, and Sisymbrieae are characterized by an additional translocation. The inferred chromosomal phylogeny provided compelling evidence for a monophyletic origin of the x=7 tribes. Moreover, chromosomal data along with previously published gene phylogenies strongly suggest the PCK to represent an ancestral karyotype of the tribe Brassiceae prior to its tribe-specific whole-genome triplication. As the PCK shares five chromosomes and conserved associations of genomic blocks with the putative Ancestral Crucifer Karyotype (n=8) of crucifer Lineage I, we propose that both karyotypes descended from a common ancestor. A tentative origin of the PCK via chromosome number reduction from n=8 to n=7 is outlined. Comparative chromosome maps of two important model species, Noccaea caerulescens and Thellungiella halophila, and complete karyotypes of two purported autotetraploid Calepineae species (2n=4x=28) were reconstructed by CCP.

MdmX Promotes Bipolar Mitosis To Suppress Transformation and Tumorigenesis in p53-Deficient Cells and Mice

Mdm2 and MdmX are structurally related p53-binding proteins that function as critical negative regulators of p53 activity in embryonic and adult tissue. The overexpression of Mdm2 or MdmX inhibits p53 tumor suppressor functions in vitro, and the amplification of Mdm2 or MdmX is observed in human cancers retaining wild-type p53. We now demonstrate a surprising role for MdmX in suppressing tumorigenesis that is distinct from its oncogenic ability to inhibit p53. The deletion of MdmX induces multipolar mitotic spindle formation and the loss of chromosomes from hyperploid p53-null cells. This reduction in chromosome number, not observed in p53-null cells with Mdm2 deleted, correlates with increased cell proliferation and the spontaneous transformation of MdmX/p53-null mouse embryonic fibroblasts in vitro and with an increased rate of spontaneous tumorigenesis in MdmX/p53-null mice in vivo. These results indicate that MdmX has a p53-independent role in suppressing oncogenic cell transformation, proliferation, and tumorigenesis by promoting centrosome clustering and bipolar mitosis.

Chromosome number reduction accompanied by extensive heterochromatin addition in the bat Glauconycteris beatrix (Mammalia; Chiroptera, Vespertilionidae)

The presumed ancestral karyotype of the bat family Vespertilionidae consists of 44 chromosomes with a fundamental number of autosomal arms (FNa) of 50. Previously, only two of the roughly 350 vespertilionid species have been reported with 2n lower than 26. In this paper we report the 2n = 22 karyotype of the African vespertilionid Glauconycteris beatrix which shows an X-autosome translocation and extended, paracentromeric, chromomycin-A3-positive heterochromatin.

Karyotypic differentiation through chromosome fusion and number reduction in Imparfinis hollandi (Ostariophysi, Heptapteridae)

The Neotropical Heptapteridae fish Imparfinis hollandi, endemic to the Iguaçu River Basin (Brazil), was cytogenetically analyzed and the diploid chromosome number of 2n = 42 chromosomes was determined (22m + 10sm + 10st), the lowest diploid number in this genus and family. Like other Heptapteridae species, only one NOR-bearing chromosome pair was detected by silver nitrate staining. Dark heterochromatic blocks were visualized in only three chromosome pairs, and chromomycin A3+ bands were coincident with Ag-NORs. Although no intercalary (TTAGGG)n sequence was observed through FISH with a telomere probe, an asymmetric karyotype showing four large chromosome pairs with diploid chromosome number reduction suggests that tandem chromosome fusions probably occurred during the karyotypic differentiation of Imparfinis hollandi.

Systematic Relationships of Hynobius okiensis among Japanese Salamanders (Amphibia: Caudata)

We conducted an electrophoretic survey to examine systematic relationships of a lotic-breeding salamander Hynobius okiensis endemic to Dogo Island of the Oki Islands, Japan, with several lentic and lotic-breeding Japanese species. Genetically H. okiensis with 2n=56 chromosomes was closer to the lentic-breeding H. nebulosus group (H. nebulosus and H. dunni) with the same chromosome number than to the lotic-breeding H. naevius group (H. naevius and H. kimurae) and H. boulengeri with 58 chromosomes. Chromosome number reduction from 58 to 56, possibly accompanied with a change in breeding environment from streams to still waters, is estimated to have first occurred in the nebulosus group of Hynobius. A reversal only in breeding habits then seems to have followed in steep, montane environments of the small island of Dogo, resulting in the speciation of H. okiensis.

In Vitro Induction of Aneuploid Forms of Tetraploid Grapes by para-Fluorophynylalanine

Mutation or somaclonal variation is one of the most useful tools in breeding of vegetatively propagated plants such as fruit trees. Mutation mainly occurs at the gene or chromosome level in a given plant. Para–fluorophenylalanine (PFP), which is an amino acid analogue, alters amino acid metabolism (Widholm, 1977), inhibits mitotic spindle formation (Thao et al., 2003) and, subsequently, reduces chromosome number to haploid number in the daughter cells (Lhoas, 1961). The effect of PFP on the reduction of chromosome number has been firstly reported in diploid Aspergillus niger from which haploid cells were induced (Lhoas, 1961). After this report, similar effects of PFP have been described in many plants such as Ribes (Knight et al., 1963), Allium (Sinha and Bhojwani, 1976), Fragaria (Niizeki and Fukui, 1983) and Alocasia (Thao et al., 2003). In Vitis, it has been reported that PFP effected on the change of chromosome number in the root cells of seedlings (Omura and Akihama, 1980; Omura et al., 1985) and induction of a triploid from PFP–treated shoots of tetraploid ‘Kyoho’ (Omura and Akihama, 1981). However, there are no reports as to somaclonal induction of hyper– and hypo–tetraploid grapes by PFP treatment. Hyper– and hypo–tetraploid grapes (2n=4x±1 or 4x±2) resulting from failure or irregularity of meiosis were found as a spontaneous (probably S1) seedling of ‘Kyoho’ (Yamane et al., 1978), appeared in selfed seedlings with abnormal cotyledons in ‘Kyoho’ (Park et al., 1999a) and rarely found in hybrid seedlings from interploid crosses between triploid and tetraploid grapes (Park et al., 1999b, 2002). ‘Takao’, a spontaneous hypotetraploid seedling of ‘Kyoho’, produces almost seedless berries of small size, but it produces large seedless berries with the aid of gibberellin treated at full bloom (Ashikawa, 1972). Thus, the crossing between tetraploid cultivars, followed by selection of the resultant seedlings with abnormal cotyledons, is an excellent method to obtain hyper– and hypo–tetraploid hybrid grapes for breeding of seedless cultivars. On the other hand, direct induction of hyper– and hypo–tetraploid forms from excellent but seeded tetraploid grape cultivars without crossings may be useful for establishing seedlessness in the seeded cultivars without greatly loosing their high tree vigor and other characters such as productivity, large berry size (Reisch and Pratt, 1996; Notsuka et al., 2000) and berry quality, although high parthenocarpy is required for the original cultivars to set and produce large–sized seedless berries without gibberellin treatment. To establish the efficient method to produce hyper– and hypo–tetraploid forms, we studied the effect of in vitro PFP treatment on the small change in tetraploid chromosome number in cultured shoots of ‘Kyoho’, colchiploid of ‘Rozaki’ and ‘Kyoho’ hybrids, all of which are tetraploid plants with relatively high parthenocarpic ability.