Showing papers on "Ploidy published in 1994"

Quantitative resistance to Phytophthora infestans in potato: a case study for QTL mapping in an allogamous plant species.

Abstract: Phytophthora infestans is the most important fungal pathogen in the cultivated potato (Solanum tuberosum). Dominant, race-specific resistance alleles and quantitative resistance--the latter being more important for potato breeding--are found in the germplasm of cultivated and wild potato species. Quantitative trait loci (QTLs) for resistance to two races of P. infestans have been mapped in an F1 progeny of a cross between non-inbred diploid potato parents with multiple alleles. Interval mapping methods based on highly informative restriction fragment length polymorphism markers revealed 11 chromosome segments on 9 potato chromosomes showing significant contrasts between marker genotypic classes. Whereas phenotypically no difference in quantitative resistance response was observed between the two fungal races, QTL mapping identified at least one race specific QT locus. Two QT regions coincided with two small segments on chromosomes V and XII to which the dominant alleles R1, conferring race specific resistance to P. infestans, Rx1 and Rx2, both inducing extreme resistance to potato virus X, have been allocated in independent mapping experiments. Some minor QTLs were correlated with genetic loci for specific proteins related to pathogenesis, the expression of which is induced after infection with P. infestans.

Chromosome abnormalities in human arrested preimplantation embryos : a multiple-probe FISH study

Abstract: Numerical chromosome abnormalities were studied in single blastomeres from arrested or otherwise morphologically abnormal human preimplantation embryos A 6-h FISH procedure with fluorochrome-labeled DNA probes was developed to determine numerical abnormalities of chromosomes X, Y, and 18 The three chromosomes were stained and detected simultaneously in 571 blastomeres from 131 embryos Successful analysis including biopsy, fixation, and FISH analysis was achieved in 865% of all blastomeres The procedure described here offers a reliable alternative to sexing of embryos by PCR and allows simultaneous ploidy assessment For the three chromosomes tested, numerical aberrations were found in 565% of the embryos Most abnormal embryos were polyploid or mosaics, and 61% were aneuploid for gonosomes or chromosome 18 Extrapolation of these results to all human chromosomes suggests that the majority of abnormally developing and arrested human embryos carry numerical chromosome abnormalities

Variations in ploidy among isolates of Botrytis cinerea : implications for genetic and molecular analyses

Abstract: Field isolates and laboratory strains of Botrytis cinerea, an ascomycetous fungus causing considerable economic losses, e.g., as “grey mould” of vine, were compared for differences in ploidy level by determining their DNA content per nucleus. Strain SAS56, an ascospore line used routinely for genetic analyses, is probably polyploid, since treatment with benomyl causes a significant reduction in DNA content per nucleus. This conclusion is substantiated by the increased sensitivity of the putative haploid derivatives to mutagens (UV and EMS). Molecular analyses (RAPD) of the haploidized strains indicate a very limited degree of heterozygosis of the parent strain SAS56. Analysis of field isolates of B. cinerea showed that their DNA content per nucleus varied considerably, indicating that aneuploidy/polyploidy is a widespread phenomenon in this species. This can explain both the variability and phenotypic instability of many field isolates of this fungus and the unusual difficulties faced by researchers in recovering stable recessive laboratory mutants. Since the haploid derivatives of SAS56 resemble the parent strain in their parasitic and physiological properties they should provide a good basis for classical and molecular genetic studies.

Dynamics of chromosome organization and pairing during meiotic prophase in fission yeast.

Abstract: Interactions between homologous chromosomes (pairing, recombination) are of central importance for meiosis. We studied entire chromosomes and defined chromosomal subregions in synchronous meiotic cultures of Schizosaccharomyces pombe by fluorescence in situ hybridization. Probes of different complexity were applied to spread nuclei, to delineate whole chromosomes, to visualize repeated sequences of centromeres, telomeres, and ribosomal DNA, and to study unique sequences of different chromosomal regions. In diploid nuclei, homologous chromosomes share a joint territory even before entry into meiosis. The centromeres of all chromosomes are clustered in vegetative and meiotic prophase cells, whereas the telomeres cluster near the nucleolus early in meiosis and maintain this configuration throughout meiotic prophase. Telomeres and centromeres appear to play crucial roles for chromosome organization and pairing, both in vegetative cells and during meiosis. Homologous pairing of unique sequences shows regional differences and is most frequent near centromeres and telomeres. Multiple homologous interactions are formed independently of each other. Pairing increases during meiosis, but not all chromosomal regions become closely paired in every meiosis. There is no detectable axial compaction of chromosomes in meiotic prophase. S. pombe does not form mature synaptonemal complexes, but axial element-like structures (linear elements), which were analyzed in parallel. Their appearance coincides with pairing of interstitial chromosomal regions. Axial elements may define minimal structures required for efficient pairing and recombination of meiotic chromosomes.

New 18S·26S ribosomal RNA gene loci: chromosomal landmarks for the evolution of polyploid wheats

Abstract: Three new 18S·26S rRNA gene loci were identified in common wheat by sequential N-banding and in situ hybridization (ISH) analysis. Locus Nor-A7 is located at the terminal area of the long arm of 5A in both diploid and polyploid wheats. Locus Nor-B6 is located in N-band 1BL2.5 of the long arm of chromosome 1B in Triticum turgidum and Triticum aestivum. ISH sites, similar to Nor-B6, were also detected on the long arms of chromosomes 1G in Triticum timopheevii and 1S in Aegilops speltoides, but their locations on the chromosomes were different from that of Nor-B6, indicating possible chromosome rearrangements in 1GL and 1BL during evolution. The third new locus, Nor-D8, was only found on the short arm of chromosome 3D in the common wheat Wichita. The loss of rRNA gene locus Nor-A3 and gain of repetitive DNA sequence pSc119 on the terminal part of 5AS suggest a structural modification of 5AS. Comparative studies of the location of the 18S·26S rRNA gene loci in polyploid wheats and putative A and B (G) genome progenitor species support the idea that: (1) Triticum monococcum subsp. urartu is the donor of both the A and At genome of polyploid wheats. (2) Ae. speltoides is closer to the B and G genome of polyploid wheats than Aegilops longissima and is the most probable progenitor of these two genomes.

Potential Markers of Prostate Cancer Aggressiveness Detected by Fluorescence in Situ Hybridization in Needle Biopsies

Abstract: Fluorescence in situ hybridization (FISH) with centromere-specific probes for chromosomes 7, 8, 11, and 12 was used to evaluate multiple 18-gauge needle biopsy cores from 50 randomly selected radical prostatectomy specimens. FISH analysis detected 26 diploid (52%), 7 tetraploid (14%), and 17 aneuploid tumors (34%). The FISH results were concordant with flow cytometric (FCM) DNA content measurements of the corresponding prostatectomy specimens for 31 tumors. For the 19 FISH/FCM discordant tumors, FISH was more sensitive than FCM for detecting ploidy anomalies. Common numerical chromosome alterations were gains of chromosomes 7 and 8, which were found in 13 (76%) and 10 (59%) aneuploid tumors, respectively. Gain of chromosome 7 was strongly associated with higher Gleason score (> or = 8) (P < 0.0001) and with advanced tumor pathological stages (stages T3 + T4; P < 0.01). Gain of chromosome 8 also correlated with higher Gleason score (P < 0.01). FISH showed intratumoral ploidy heterogeneity in 3 of 41 (7%) studied tumors. Among 17 noncancerous adjacent tissue specimens, chromosome alterations were observed in one, which contained high-grade prostatic intraepithelial neoplasia. Combined FISH and fluorescent leukocyte common antigen staining showed that infiltrating leukocytes do not contribute to the observed gains of chromosomes 7 and 8 in prostate cancer tissue. These results demonstrate that (a) FISH analysis of prostate needle biopsy-sized specimens can be a practical, sensitive method for determination of nuclear ploidy and numerical chromosome alterations; and (b) gains of chromosomes 7 and 8 are common numerical alterations of prostate cancer cells and may be potential markers of tumor behavior and patient prognosis.

The chromosome constitution of human preimplantation embryos fertilized in vitro

Abstract: The chromosome constitution of five haploid, 178 diploid and 11 triploid embryos fertilized in vitro was determined after fixation on day 2 or day 3 of development. Karyotype analysis of 178 diploid embryos revealed abnormalities in 40 (22.5%) cases: 34 (19.1%) aneuploids, four (2.2%) mosaic embryos and two (1.1%) structural anomalies were identified. The majority of aneuploid karyotypes (28/34) involved a single chromosome but six embryos had aneuploidy of two or three chromosomes. The E group was most frequently involved in aneuploid karyotypes (10/23 hyperdiploid embryos) and trisomy 16, the most common single anomaly in diploid embryos, was detected in 2.2% (4/178) of cases. Only one case of sex chromosome monosomy was identified. An excess of female karyotypes was detected in abnormal cases (sex ratio 0.48); this ratio was significantly (P < 0.05) different from that observed in normal cases (74:64, XY:XX). The incidence of aneuploidy increased with maternal age but this did not reach statistical significance. Embryo morphology and growth rate, assessed by embryo development rating (EDR), did not distinguish between normal (mean score 7.9; mean EDR 96.1) and aneuploid (mean score 8.1; mean EDR, 92.1) embryos. Numbers of hyperploid (n = 17) and hypoploid (n = 11) embryos (non-mosaic cases involving single chromosomes) were not statistically different. The relative proportions of chromosomes involved in trisomic karyotypes showed a remarkable similarity to the pattern in spontaneous abortions. Pronuclear status was an unreliable predictor of ploidy. Small numbers of karyotyped triploid embryos revealed equal proportions of XXX, XXY and XYY embryos.

Genomic in situ hybridization in Avena sativa.

Abstract: Genomic fluorescent in situ hybridization was employed in the study of the genome organization and evolution of hexaploid oat (Avena sativa L. cv. Sun II, AACCDD, 2n = 6x = 42). Genomic DNAs from two diploid oat species, Avena strigosa (genomic constitution AsAs, 2n = 14) and Avena pilosa (genomic constitution CpCp, 2n = 14), were used as probes in the study. The DNA from A. strigosa labelled 28 of the 42 (2/3) chromosomes of the hexaploid oat, while 14 of the 42 (1/3) chromosomes were labelled with A. pilosa DNA, indicating a close relationship between the A and D genomes. Results also suggested that at least 18 chromosomes (9 pairs) were involved in intergenomic interchanges between the A and C genomes.

Numerical chromosome abnormalities in spermatozoa of fertile and infertile men detected by fluorescence in situ hybridization.

Abstract: Fluorescence in situ hybridization (FISH) with single-color chromosome-specific probes was used to study the rates of disomy for chromosome 1, 16, X, and Y in sperm of fertile and infertile subjects. Diploidy rates were studied using a two-color cocktail of probes for chromosomes 17 and 18 in the same sperm samples. Two-color methodology was not available at the outset of the study. A total of 450,580 spermatozoa were studied from 21 subjects (9 fertile, 12 infertile). Significant differences were observed in the disomy rates between chromosomes with the highest frequency observed for chromosome 16 (0.17%) and the lowest for the Y chromosome (0.10%). No differences were observed between fertile and infertile subjects for either diploidy or disomy. Total disomy rates for chromosomes 1, 16, X and Y ranged from 0.34% to 0.84% among infertile subjects, and 0.32% to 0.61% among fertile subjects. Our data suggest that generalized aneuploidy in sperm is not a major contributor to unexplained infertility.

Development of monosomic alien addition lines and introgression of genes from Oryza australiensis Domin. to cultivated rice O. sativa L.

Abstract: Oryza australiensis, a diploid wild relative of cultivated rice, is an important source of resistance to brown planthopper (BPH) and bacterial blight (BB). Interspecific hybrids between three breeding lines of O. sativa (2n=24, AA) and four accessions of O. australiensis (2n=24, EE) were obtained through embryo rescue. The crossability ranged from 0.25% to 0.90%. The mean frequency of bivalents at diakinesis/metaphase I in F1 hybrids (AE) was 2.29 to 4.85 with a range of 0–8 bivalents. F1 hybrids were completely male sterile. We did not obtain any BC1 progenies even after pollinating 20,234 spikelets of AE hybrids with O. sativa pollen. We crossed the artificially induced autotetraploid of an elite breeding line (IR31917-45-3-2) with O. australiensis (Acc. 100882) and, following embryo rescue, produced six F1 hybrid plants (AAE). These triploid hybrids were backcrossed to O. sativa. The chromosome number of 16 BC1 plants varied from 28 to 31, and all were male sterile. BC2 plants had 24–28 chromosomes. Eight monosomic alien addition lines (MAALs) having a 2n chromosome complement of O. sativa and one chromosome of O. australiensis were selected from the BC2 F2 progenies. The MAALs resembled the primary trisomies of O. sativa in morphology, and on the basis of this morphological similarity the MAALs were designated as MAAL-1, -4, -5, -7, -9, -10, -11, and -12. The identity of the alien chromosome was verified at the pachytene stage of meiosis. The alien chromosomes paired with the homoeologous pairs to form trivalents at a frequency of 13.2% to 24.0% at diakinesis and 7.5% to 18.5% at metaphase I. The female transmission rates of alien chromosomes varied from 4.2% to 37.2%, whereas three of the eight MAALs transmitted the alien chromosome through the male gametes. BC2 progenies consisting of disomic and aneuploid plants were examined for the presence of O. australiensis traits. Alien introgression was detected for morphological traits, such as long awns, earliness, and Amp-3 and Est-2 allozymes. Of the 600 BC2 F4 progenies 4 were resistant to BPH and 1 to race 6 of BB. F3 segregation data suggest that earliness is a recessive trait and that BPH resistance is monogenic recessive in two of the four lines but controlled by a dominant gene in the other two lines.

Estimating Nuclear DNA Content in Peach and Related Diploid Species Using Laser Flow Cytometry and DNA Hybridization

Abstract: Using laser flow cytometry, nuclear DNA amounts were estimated for 12 Prunus species, representing three subgenera (Prunophora (Prunus), Amygdalus, and Cerasus (Lithocerasus)), two interspecific hybrids, four cultivars, and a synthetic polyploid series of peach consisting of haploids, diploids, triploids, and tetraploids (periclinal cytochimeras). Peach nuclear DNA content ranged from 0.30 pg for the haploid nuclei to 1.23 pg for the tetraploid nuclei. The diploid genome of peach is relatively small and was estimated to be 0.60 ± 0.03 pg (or 5.8 × 10 8 nucleotide base pairs). The polyploid series represented the expected arithmetic progression, as genome size positively correlated with ploidy level (i.e., DNA content was proportional to chromosome number). The DNA content for the 12 diploid species and two interspecific diploid hybrids ranged from 0.57 to 0.79 pg. Genome size estimates were verified independently by Southern blot analysis, using restriction fragment length polymorphism clones as gene-copy equivalents. Thus, a relatively small and stable nuclear genome typifies the Prunus species investigated, consistent with their low, basic chromosome number (x = 8).

Spontaneous hybridization between a male-sterile oilseed rape and two weeds

Abstract: Spontaneous interspecific hybrids were produced under natural conditions (pollination by wind and bees) between a male-sterile cybrid Brassica napus (AACC, 2n = 38) and two weeds Brassica adpressa (AdAd, 2n = 14) and Raphanus raphanistrum (RrRr, 2n = 18). After characterization by chromosome counts and isozyme analyses, we observed 512 and 3 734 inter-specific seeds per m(2) for the B. napus-B. adpressa and B. napus-R. raphanistrum trials respectively. Most of the hybrids studied had the expected triploid structure (ACX). In order to quantify the frequency of allosyndesis between the genomes involved in the hybrids, their meiotic behavior was compared to a haploid of B. napus (AC). For the B. napus-B. adpressa hybrids, we concluded that probably no allosyndesis occurred between the two parental genomes, and that genetic factors regulating homoeologous chromosome pairing were carried by the B. adpressa genome. For the B. napus-R. raphanistrum hybrids, high chromosome pairing and the presence of multivalents (in 9.16% of the pollen mother cells) indicate that recombination is possible between chromosomes of different genomes. Pollen fertility of the hybrids ranged from 0 to 30%. Blackleg inoculation tests were performed on the three parental species and on the interspecific hybrids. BC1 production with the weeds and with rapeseed was attempted. Results are discussed in regard to the risk assessment of transgenic rapeseed cultivation, F1 hybrid rapeseed variety production, and rapeseed improvement.

The asexual ploidy cycle and the origin of sex.

Abstract: Sex involves syngamy (gamete fusion), which doubles the amount of DNA in a cell, and meiosis, which halves it. The result is a 'ploidy cycle' of alternating diploid and haploid phases. Asexual reproduction does not require changes of ploidy, and yet asexual forms may have ploidy cycles. Here I show that such cycles lessen the mutation load, compared with permanent diploidy or polyploidy, and are thus likely to evolve in cases where it is always advantageous to have more than one copy of the genome per cell. The asexual ploidy cycle could have facilitated the origin of sex, by providing a means of orderly genetic reduction available immediately after the origin of syngamy.

Sensitive detection of chromosome copy number aberrations in prostate cancer by fluorescence in situ hybridization.

Abstract: The pattern of chromosomal aberrations and their significance in prostate cancer are poorly understood. We studied 23 prostate cancer and 10 benign prostatic hyperplasia (BPH) specimens by fluorescence in situ hybridization (FISH) using pericentromeric repeat-specific probes for 10 different chromosomes. The aims of the study were: 1) to compare the sensitivity of FISH and DNA flow cytometry in aneuploidy detection, 2) to determine which chromosome copy number changes are most common, and 3) which probe combinations would be most effective in aneuploidy diagnosis. Disaggregated tumor cells from formalin-fixed, paraffin-embedded tissues were pretreated with our newly developed method based on hot glycerol solution to improve probe penetration. All BPH specimens were diploid by DNA flow cytometry and showed no numerical chromosome aberrations by FISH. In prostate cancer, flow cytometry showed abnormal DNA content in 35% of cases, whereas 74% were abnormal by FISH. Aberrant copy number of chromosomes 8 (48% of cases), X (43% of cases), and 7 (39% of cases) were most common. Ninety-four percent of all aneuploid cases would have been detected with these three probes alone. Simple chromosome losses were uncommon but in DNA tetraploid tumors relative losses (trisomy or disomy) of several chromosomes were often found, suggesting progression of prostate cancer through tetraploidization followed by losses of selected chromosomes. In conclusion, our results indicate that FISH using three selected chromosome-specific probes is two to three times more sensitive than flow cytometric DNA content analysis in aneuploidy detection.

Evolution of Number and Morphology of Mammalian Chromosomes

Abstract: Numerous hypotheses have been advanced to explain how selection might operate on the level of the chromosomal complement (chromosome selection) and how this process could be related to morphological divergence and speciation. Hypotheses emphasizing a general trend of increasing or decreasing diploid numbers in mammalian evolution are contradicted by documented studies from diverse families of mammals. However, certain selective forces were identified that could drive chromosomal evolution in certain lineages under limited conditions. Species with higher fundamental numbers and/or higher diploid numbers are expected to have increased genetic recombination. Increased recombination is advantageous in increasing variability and thus utilization of a wider niche, but decreased recombination allows fixation of new mutations (both genic and chromosomal) and thus increased potential for phyletic divergence and speciation. The species with higher diploid numbers are also less likely to undergo deleterious translocation and inversion events because of the position of the chromosomes in the nucleus. A decrease in diploid or fundamental numbers by fusions or inversions would be important as an initial event in phyletic divergence in some groups. A rearrangement in one chromosome also could affect nuclear structure or recombination in other chromosomes and, in some lineages, could drive the acquisition of additional rearrangements. It is suggested that changes in the level of recombination and in nuclear stability played a pivotal role in mammalian chromosome evolution.

Improved Techniques for Haploid Production in Wheat using Chromosome Elimination

Abstract: Wheat × maize and wheat × pearl millet crosses have proved efficient for haploid production using various genotypes of wheat; 22 and 27 % of florets produced embryos. In favourable conditions 6—9 haploid plants per spike were produced. The following simplifications or improvements in technique are recommended: 1. Only a single treatment with an aqueous solution of dicamba or 2,4-D (50–100 ppm) for embryo stimulation in vivo; 2. Application by spraying or dipping the spikes; 3. Application time two to four days after pollination; 4. Embryo rescue 15 to 18 days after pollination; 5. Crosses without emasculation are possible if pollination occurs 1–2 days before anthesis. More than 450 haploids and some doubled haploid (DH) lines (after colchicine treatment in vitro) were produced using these methods. No hybrid plants, chromosome additions or substitutions were found.

Properties of maternal haploid maize plants and potential application to maize breeding

Abstract: Presented are the results of a two-year study of haploid maize plants in the field. The haploids were produced with the aid of inducer line ZMS. In total, 604 and 1030 haploids were obtained and studied in the first and second years, respectively. Tassels of haploid plants were found to be almost completley sterile. Fertility of ears was studied by pollinating them with the pollen from diploid inbred lines, the cross resulting in almost all of the haploid ears carrying kernels. On average 27.4 kernels per ear of haploid plant were obtained in the first year of study and 26.3 in the second. These gave rise to normal diploid plants. This property allows genotypes selected at the level of haploid plants to be involved in breeding process. Unusual plants were found among haploids, phenotypically resembling homozygous lines. It was assumed that the plants had resulted from spontaneous chromosome doubling in haploids. The results of comparative studies of progenies of unusual plants and inbred lines derived from the same synthetic population are presented.

A molecular approach to unraveling the genetics of sugarcane, a complex polyploid of the Andropogoneae tribe.

Abstract: Modern sugarcane varieties are complex aneuploids and typically have chromosome numbers in the 100–125 range with about 5–10% of them contributed by wild relatives, mainly Saccharum spontaneum, and the rest by S. officinarum. This particular genomic constitution was found favorable for mapping the S. spontaneum genome, using maize as a diploid reference for comparison. We conducted an analysis of 32 individuals derived from the selfing of variety SP 701006 using four isozymes and 53 maize probes which covered the whole maize genome. A total of 348 segregating bands were generated. Highly significant cosegregations enabled us to place 94 markers into 25 cosegregation groups. Eighteen of these groups involved S. spontaneum specific markers and might therefore mark S. spontaneum chromosomes in segregation. On the basis of probes in common, the 25 cosegregation groups could be assembled into eight tentative linkage groups, of which seven describe S. spontaneum chromosomes. A large degree of synteny between su...

RFLP markers associated with Sr22 and recombination between chromosome 7A of bread wheat and the diploid species Triticum boeoticum.

Abstract: Analysis of the bread wheat variety Schomburgk, and related lines in its pedigree, identified RFLP markers associated with the segment of chromosome 7A carrying the Sr22 gene derived from the diploid species T boeoticum The distribution of the RFLP markers indicated that at least 50% of 7AS and 80% of 7AL in Schomburgk is of T boeoticum origin Evaluation of five sets of nearisogenic lines, backcross lines in 20 different genetic backgrounds and an F2 population segregating for Sr22 demonstrated a very low level of recombination between the 7A chromosomes of T boeoticum and T aestivum Several recombinants carrying Sr22 but with a much reduced segment of T boeoticum were identified and these may prove useful in the breeding of further varieties with Sr22

Allodiploid nature of Allium wakegi Araki revealed by genomic in situ hybridization and localization of 5S and 18S rDNAs.

Abstract: Allium wakegi Araki could be originated from cross hybridization between close relatives of a form of A. cepa and A. fistulosum. Chromosomes of each parental haploid set were identified in the chromosome complement of A. wakegi by genomic in situ hybridization using probes of the total, parental genomic DNAs of A. cepa and A. fistulosum, respectively. The results of GISH suggested significant differentiation of genomic DNAs between these closely related species. Allium cepa had two 5S rDNA loci at the interstitial regions of the short arms of small chromosome pair (the 7th pair) and A. fistulosum had one locus at the interstitial region of the homologous short arms. Allium wakegi had two chromosomes carrying one and two 5S rDNA loci which appeared to correspond to those of A. fistulosum and A. cepa, respectively. Chromosomes carrying 18S rDNA loci originated from those of both A. cepa and A. fistulosum were also observed in the chromosome complement of A. wakegi.

Quantitative trait locus analysis of tuber dormancy in diploid potato (Solanum spp.).

Abstract: Quantitative trait locus (QTL) analysis for tuber dormancy was performed in a diploid potato population (TRP133) consisting of 110 individuals. The female parent was a hybrid between haploid S. tuberosum (2x) and S. chacoense, while the male parent was a S. phureja clone. The population was characterized for ten isozyme loci, 44 restriction fragment length polymorphisms (RFLPs) and 63 random amplified polymorphic DNAs (RAPDs). Eighty-seven of these loci segregating from the female parent were utilized to develop a linkage map that comprised 10 of the 12 chromosomes in the genome. Dormancy, as measured by days-to-sprouting after harvest, ranged from 10 to 90 days, with a mean of 19 days. QTLs were mapped by conducting one-way analyses of variance for each marker locus by dormancy combination. Twenty-two markers had a significant association with dormancy, identifying six putative QTLs localized on each of chromosomes 2, 3, 4, 5, 7 and 8. The QTL with the strongest effect on dormancy was detected on chromosome 7. A multilocus model was developed using the locus with highest R2 value in each QTL. This model explained 57.5% of the phenotypic variation for dormancy. Seven percent of possible epistatic interactions among significant markers were significant when tested through two-way analyses of variance. When these were included in the main-effects model, it explained 72.1% of the phenotypic variation for dormancy. QTL analysis in potato, the methodology to transfer traits and interactions into the 4x level, and QTLs of value for marker-assisted selection, are discussed.

Mapping in the realm of polyploidy: The wheat model

Abstract: Wheat is an allopolyploid containing three distinct but genetically related (homoeologous) genomes, A, B and D. Because of polyploid inheritance and large genome size (16×1012 bp), the wheat genome is thought to be intractable to map-based cloning of agronomic and other genes of interest. We propose a targeted geneti mapping strategy that combines linkage and physical mapping and may facilitate map-based cloning. High-density linkage maps are either generated in wheat or in diploid Triticum tauschii, the donor of the D genome to wheat. Molecular marker-based chromosome maps are constructed, using an array of deletion lines in wheat. The conventional genetic linkage maps are aligned with chromosome maps to construct cytogenetic ladder maps (CLMs). The CLMs allow region-specific mapping and convert genetic distances into physical distances. The information from CLMs suggests that many genes in wheat are present in clusters that are highly recombiogenic, small, and may be amenable to cloning by chromosome walking. Therefore, the effective genome size of wheat is relatively small in comparison to the whole genome. The utility of using the smaller genome of rice for mapping and homologous gene cloning is discussed.

Easy determination of ploidy level in Arabidopsis thaliana plants by means of pollen size measurement

Abstract: Cytogenetic examination of transgenic Arabidopsis thaliana (L.) Heynh. plants obtained by Agrobacterium-mediated gene transfer to cotyledon- and root-explants or by direct gene transfer into protoplasts revealed a high percentage of tetraploid or aneuploid transformants. Depending on the transformation procedure used, 13% (root explant transformation), 33% (cotyledon explant transformation), or 38% (direct gene transfer) of the transformants showed aberrant ploidy levels. A good correlation between the ploidy level of a plant and the size of its pollen grains was observed. This allows quick and simple testing of the ploidy level of transgenic Arabidopsis plants.

Oryzalin as an Efficient Agent for Chromosome Doubling of Haploid Apple Shoots in vitro

Abstract: In an outbreeding species such as apple, haploid plants may be especially useful in breeding programmes for the production of homozygous material. However, methods must be available to induce chromosome doubling in the haploid plants. Two antimitotic agents, colchicine and oryzalin, were compared as regards their efficiency in inducing chromosome doubling of in vitro haploid apple shoots. Three colchicine levels (0.025, 0.25 and 1.25 mM) and three oryzalin levels (5, 15 and 30 μM) were evaluated. Three techniques were also used and compared. Survival rate and chromosome counts were determined. Differences were observed between the two antimitotic agents and between the three techniques. This study demonstrates that oryzalin could be a better choice than colchicine for chromosome doubling on haploid apple shoots in vitro.

Geographical variation of heterochromatin in Ctenomys flamarioni (Rodentia-Octodontidae) and its cytogenetic relationships with other species of the genus

Abstract: The first karyotype analysis of Ctenomys flamarioni, based on a sample of 46 specimens collected along the geographical range of this species, is reported. All specimens exhibited a diploid number of 48 but varied in autosomal arm number from a low of 50 to a high of 78. The amount of constitutive heterochromatin also varied with the species’ geographical distribution. Comparison of G-band patterns showed a strong relationship between the karyotype of this species and those belonging to the Argentinian mendocinus group.

Somatic hybrids between Solanum etuberosum and diploid, tuber bearing Solanum clones.

Abstract: Electrofusion was used to obtain somatic hybrids between Solanum etuberosum (2n=2x=24) and two diploid potato lines. These hybridizations were conducted to determine if haploidxwild species hybrids are better fusion partners than conventional S. tuberosumGp. Tuberosum haploids. Restriction fragment length polymerase (RFLP) analyses of the putative somatic hybrids confirmed that each parental genome was present. The somatic hybrids between S. etuberosum and a haploid S. tuberosum clone, US-W730, were stunted and had curled, purple leaves. In contrast, somatic hybrids between S. etuberosum and a haploidxwild species hybrid (US-W 730 haploidx S. berthaultii), were vigorous and generally tuberized under field conditions. These hybrids were designated as E+BT somatic hybrids. Analyses of 23 E+BT somatic hybrids revealed a statistically significant bias towards the retention of S. etuberosum chloroplasts. Stylar incompatibilities were observed when the E+BT somatic hybrids were used as pollen donors in crosses with S. tuberosum cultivars. Reciprocal crosses did not show this incompatibility. The progeny were vigorous and had improved tuber traits when compared to the maternal E+BT parent. RFLP analyses of three sexual progeny lines confirmed the presence of all 12 S. etuberosum chromosomes. In two of these lines, RFLPs that marked each of the 24 chromosome arms of S. etuberosum were present. However, RFLP markers specific for regions on chromosomes 2, 7, and 11 were missing from the third clone. Because other markers for these chromosomes were present in the progeny line, these results indicated the likelihood of pairing and recombination between S. etuberosum and S. tuberosum chromosomes.

Mitotic and meiotic irregularities in somatic hybrids of Lycopersicon esculentum and Solanum tuberosum.

Abstract: Chromosome numbers were determined in metaphase complements of root-tip meristems of 107 tomato (+) potato somatic hybrids, obtained from five different combinations of parental genotypes. Of these hybrids 79% were aneuploid, lacking one or two chromosomes in most cases. All four hybrids that were studied at mitotic anaphase of root tips showed laggards and bridges, the three aneuploids in a higher frequency than the single euploid. Hybrid K2H2-1C, which showed the highest percentage of aberrant anaphases, possessed 46 chromosomes. Fluorescence in situ hybridization with total genomic DNA showed that this hybrid contained 23 tomato, 22 potato, and 1 recombinant chromosome consisting of a tomato chromosome arm and a potato chromosome arm. The potato parent of K2H2-1C was aneusomatic in its root tips with a high frequency of monosomic and trisomic cells and a relatively high frequency of cells with one fragment or telosome. Meiotic analyses of three tomato (+) potato somatic hybrids revealed laggards, which...