Conjugation Of Chromosomes Research Articles

Crossing and Setting of Hybrid Seeds in the Creation of Chromosome-Substituted Cotton Lines g. Hirsutum l.

A comparative study of the indicators of crossability and setting of hybrid and backcross seeds F1, F1BC1, F1BC2, obtained from crossings of monosomic and monotelodisomic lines of cotton G.hirsutum L. with the donor line Pima 3-79 of the species G.barbadense L. and aneuploid backcross hybrids, was found to be a linear decrease of these indicators in some hybrids, as well as their increase, as well as the alternation of indicators of crossability and setting in different hybrid generations. The study of chromosome conjugation in hybrid monosomic F1 obtained from crossing monosomic lines with the donor line Pima 3-79 of the species G. barbadense L., as well as backcross monosomic F1BC1, F1BC2 with the replacement of specific chromosomes of the cotton genome, revealed normal chromosome conjugation with the formation of 25 bivalents and one univalent of different size in all studied PMCs in most hybrids.

Genomic and Cytogenetic Analysis of Synthetic Polyploids between Diploid and Tetraploid Cotton (Gossypium) Species.

Cotton (Gossypium spp.) is the most important natural fiber source in the world. The genetic potential of cotton can be successfully and efficiently exploited by identifying and solving the complex fundamental problems of systematics, evolution, and phylogeny, based on interspecific hybridization of cotton. This study describes the results of interspecific hybridization of G. herbaceum L. (A1-genome) and G. mustelinum Miers ex Watt (AD4-genome) species, obtaining fertile hybrids through synthetic polyploidization of otherwise sterile triploid forms with colchicine (C22H25NO6) treatment. The fertile F1C hybrids were produced from five different cross combinations: (1) G. herbaceum subsp. frutescens × G. mustelinum; (2) G. herbaceum subsp. pseudoarboreum × G. mustelinum; (3) G. herbaceum subsp. pseudoarboreum f. harga × G. mustelinum; (4) G. herbaceum subsp. africanum × G. mustelinum; (5) G. herbaceum subsp. euherbaceum (variety A-833) × G. mustelinum. Cytogenetic analysis discovered normal conjugation of bivalent chromosomes in addition to univalent, open, and closed ring-shaped quadrivalent chromosomes at the stage of metaphase I in the F1C and F2C hybrids. The setting of hybrid bolls obtained as a result of these crosses ranged from 13.8-92.2%, the fertility of seeds in hybrid bolls from 9.7-16.3%, and the pollen viability rates from 36.6-63.8%. Two transgressive plants with long fiber of 35.1-37.0 mm and one plant with extra-long fiber of 39.1-41.0 mm were identified in the F2C progeny of G. herbaceum subsp. frutescens × G. mustelinum cross. Phylogenetic analysis with 72 SSR markers that detect genomic changes showed that tetraploid hybrids derived from the G. herbaceum × G. mustelinum were closer to the species G. mustelinum. The G. herbaceum subsp. frutescens was closer to the cultivated form, and its subsp. africanum was closer to the wild form. New knowledge of the interspecific hybridization and synthetic polyploidization was developed for understanding the genetic mechanisms of the evolution of tetraploid cotton during speciation. The synthetic polyploids of cotton obtained in this study would provide beneficial genes for developing new cotton varieties of the G. hirsutum species, with high-quality cotton fiber and strong tolerance to biotic or abiotic stress. In particular, the introduction of these polyploids to conventional and molecular breeding can serve as a bridge of transferring valuable genes related to high-quality fiber and stress tolerance from different cotton species to the new cultivars.

Polyploidy in the history of breeding at the Yaltushkiv Experimental Breeding Station: new methods of differentiation and stabilisation of sugar beet tetraploids

Purpose. To analyse the history of the polyploid breeding at the Yaltushkiv Experimental Breeding Station, in particular the improvement of genetic models of new hybrids, new methods of induction of meiotic tetraploids, differentiation and selection of breeding genotypes by genome ploidy.
 Methods. Cytological analysis of metaphase chromosomes of the apical meristems of the growth points of seed plants and beets of the first year for the selection of tetraploid plants 4x = 36 chromosomes; cytophotometric analysis using computer programs AP Partec to study ploidy based on the quantitative content of nuclear DNA; field methods (selection of tetraploid seed plants according to the types of pollen grains, formation of synthetic populations of tetraploid multigerm plants on a cytogenetic basis according to the structure of bivalent conjugation of homologous chromosomes in meiosis.
 Results. In the process of tetraploid induction, cytological methods of ploidy analysis at the station were improved using computer programs of AP Partec for the selection of sugar beets 4x by the quantitative content of nuclear DNA in the cell on plants of the first year of vegetation and for the formation of tetraploid populations after colchicine induction in seed plants. In the process of studying the structure of polyploid populations by ploidy, the percentage of tetraploids varied from 82.0±2.22% in Ya/Hen pollinator to 58.1±2.81% in Ya/Man pollinator. It was established that the selection for fertility and pollen uniformity depends on the genetic characteristics of the breeding genotypes and affects the pollen-forming ability in the first generations after induction with colchicine, reducing the number of 4x IIa and IIb biotypes according to cytological classification. Using the example of the multigerm pollinator Ya/Roi, it was established that selection for sugar content and productivity had, to a certain extent, a stabilising effect on the degree of ploidy. The biotechnological methods used to deposit 4x genotypes with a high percentage of bivalent conjugation of homologous chromosomes in metaphase I of meiosis (70–90%) contributed to the cytogenetic stability of polyploid gametes and their high yield – 92.9% of 4x in the next generation of seeds. It was investigated that the productivity of triploid hybrids obtained with the use of the tetraploid pollinator Ya/DA 4x based on the germplasm of the wild species Beta patula at the early stages of vegetative development varied in triploid plants from 325 to 465 g, and the sugar content in some numbers reached 21.5%.
 Conclusions. The development of polyploid selection at the Yaltushkiv Experimental Breeding Station evolved from the development polyhybrids to the development of triploid hybrids based on CMS using tetraploid multigerm pollinators. For the formation of populations of tetraploid multigerm pollinators, the methods of fluorescent cytophotometry and computer programs AP Partec were used, as well as biotechnological methods for creating synthetic populations of tetraploid multigerm pollinators on a cytogenetic basis, which ensure the yield of tetraploids in seeds up to 92.9%.

Cytogenetic Analysis of F1Hybrids Derived From Crossings of Triticum aestivum L. Lines With Aegilops L. Species

As a result of the studies seed settings of hybrid combinations obtained from the crossings between Triticum aestivum L. lines and Aegilops L. species, also the cytogenetic analysis of the F1 hybrids belonging to these combinations have been established that possession joint subgenomes of parental forms is not guarantee a relatively high percentage of fertility at crosses, and a high level of chromosome pairing in meiosis. At the same time, no significant correlations were found between the level of chromosome conjugation and fertility in the studied intergeneric F1 hybrids.

Tandem duplications, eupolyploidy and secondary diploidization – genetic mechanisms of plant speciation and progressive evolution

The article considers the genetic mechanisms of plant speciation. The importance of interspecific hybridization and polyploidy (whole genome duplication, WGD) as the main mechanisms of plant speciation is shown. There are three main ways of transformations of the hybrid genome associated with speciation. In the first way, the ploidy of the offspring does not change in comparison with the parents’ ploidy; the genomes of hybrid lines are stabilized through backcrosses and introgression without polyploidization. In the second way, the interspecial hybridization followed by whole genome duplication. Then, the initially unstable neopolyploid genome gradually passes into a stable eupolyploid state with the preservation of the polyploid number of chromosomes but with the diploid type of chromosome conjugation in meiosis. This is a widespread and rapid mechanism of plant speciation and genus formation in higher plants, which ensured the morphological and genetic isolation and adaptability of at least 15 % of modern species of higher plants. However, this is a path that usually does not lead to aromorphoses, this is speciation at an already achieved level of complexity. The third way of speciation is realized through dysploidy and secondary diploidization of the genome. In this case, the neopolyploid undergoes significant genomic rearrangements and loses most of the duplicated gene copies, its number of chromosomes is radically reduced. In different individuals of a species that has embarked on the path of stochastic genome fractionation and dysploidy, the initial genetic redundancy of various genome components multiplied after WGD is transformed in an unpredictably unique way, which leads to a radical increase in intraspecific genomic and epigenetic polymorphism and provides rich material for natural selection. It was also shown that in eupolyploids and paleopolyploids, a significant role in heritable adaptations to environmental conditions and in anatomical and morphological innovations is played by segment and tandem duplications not associated with WGD. Some of the paleopolyploids, which turned out to be evolutionarily progressive morphotypes, possessing aromorphoses with diploidized genomes, give rise to new phylogenetic branches, new suprageneric taxa. The article proposes to assign both genera carrying a unique two-chromosomal genome Zingeria and Colpodium (x = 2; 2n = 4, 8, 12) into subtribe Zingeriinae Rodionov, subtrib. nov. – Type: Zingeria P. A. Smirn. In addition, the accomodation of the genera Helictochloa and Molineriella into one subtribe Helictochloinae Röser et Tkach seems to us unreasonable from a genomic point of view, since the fundamental difference between representatives of these two genera is that Molineriella species carry an unusual 4-chromosomal genome, while speciation in genus Helictochloa(2n = 14 – 154) goes through the combinations of different 7-chromosome subgenomes, denoted by the letters E, L, B, C, M, V, G, U. Therefore, we consider it necessary to assign Molineriella into a monogenic subtribe MolineriellinaeRodionov, subtrib. nov. – Type: Molineriella Rouy.

Analysis of Aggressive Behavior in Young Russian Males Using 250 SNP Markers

Until not so long ago, the main area of genetic studies of aggressive behavior was represented by associative analysis of candidate genes, which were identified according to the relationship of phenotypic manifestations of aggression with the functioning of neuromediator and reproductive systems. Recent years have been marked by development of a new direction of genome-wide associative studies of aggression, which makes it possible to detect new genes that previously were not the object of interest to specialists. The present study is an analysis of aggressive behavior in Russian males living in the Moscow metropolis, using a panel of 250 SNP marker loci. In addition to SNP markers of known candidate genes, the panel contained single base substitutions in genes involved in the development and functioning of the brain, in the processes of neuronal development and synaptic plasticity, and in the formation of interneuronal connections, as well as in genes associated with various brain pathologies. The panel of SNP markers also included control genes that were in no way associated with aggressive behavior or behavior in general. These are primarily housekeeping genes, as well as genes encoding proteins associated with chromatid cohesion, etc. Aggressive behavior was self-assessed using the Bass–Perry and reactive–proactive aggression questionnaires. After applying a number of filters, 35 males were included in the final sample. Fragments containing 250 single-nucleotide polymorphic sites of interest were sequenced on the Ion PGM System using the Ion 318™ Chip. The principal component analysis and clustering based on the Bayesian a posteriori probability did not identify subdivisions in the analyzed sample of Russian males. For each aggression scale, a statistically significant association with a specific set of SNP markers was obtained, and only one polymorphic locus rs1047788 was associated with both physical and reactive aggression. Bioinformatic analysis revealed that most of the identified markers are associated with neuropeptides involved in the development and functioning of the nervous system as a whole and its regeneration and in the development of sections of the brain responsible for stress reactions, regulation of the humoral system, and intercellular signaling. For a number of markers from this set, it was possible to identify possible mechanisms of relationship to behavioral traits. The list of identified genes is as follows: corticotropin-releasing hormone, CRH; semenogelin-1 protein, SEMG1; intercellular interaction proteins, LAMC2 and ITGA2; DNA repair endonuclease, ERCC5; cohesin complex protein that provides conjugation of sister chromosomes, ESCO1; transmembrane serine protease, TMPRSS15; apoptosis inhibitor, BIRC5; interferon beta-1, IFNB1; scaffold protein, XRCC1; heat shock protein, HSP90AA1.

Cytological stability of wheat amphidiploids and cultivars in meiosis I

Introgression of genes controlling useful traits into a common wheat gene pool is still a highly actual task. Amphidiploids usually serve as a bridge for transferring alien genes into the wheat genome. One of the conditions of successful use of amphidiploids as sources of alien genes is their cytological stability and fertility. Cytological stability of the genome substitution amphidiploids Aurotica and Auroale was determined through characterization of different meiosis stages by studding cytological preparations. Amphidiploids were characterized by deviations from the bivalent chromosome conjugation, appearance of multivalent chromosome associations, and univalent chromosomes in metaphase I. In the anaphase, bridges were observed. Univalents and chromosome fragments resulted from the bridges breakage caused appearance of micronuclei in tetrads. Conjugation of chromosomes in common wheat cultivars, studied for comparison, was bivalent, with the absolute preference of closed bivalents in metaphase plates. The meiotic index calculated on quantitative characteristics of amphidiploids with micronuclei and polyads was similar for Aurotica and Auroale and varied between 64–69 %. In tetrads of Auroale no triads were found, whereas in Aurotica triads were usual. So, the meiotic index in itself is not an indicator for the meiotic stability of a plant sample. More exhaustive information can be received through structuring of the meiotic index for assessment of components which are used for its calculation. The received results enable to assume that meiotic abnormalities in Aurotica may be caused by disorder of synchrony in meiosis II processes, whereas for Auroale this disorder is not typical. Gametogenesis in amphidiploids sometimes demonstrated appearance of the third generative nucleus in the male gametophyte. Determined meiosis characteristics explain the decline in seed fertility of Aurotica, and in particular Auroale, compared to common wheat cultivars.Manuscript received 13.04.2020

Inheritance of powdery mildew resistance in Aurotica’s introgressive lines

Aim. Frequency of alien chromatin inheritance in hybrids from crosses of common wheat and introgressive lines determines whether transfer of alien chromatin controlling desirable trait into common wheat genome would be successful. The paper presents results of introgressive lines assessment for frequency of transfer of alien dominant trait of powdery mildew resistance to their progeny in the crossing with recurrent genotype Aurora, which was a recipient cultivar in the development of these lines. Methods. Artificial hybridization of introgressive lines with common wheat, visual assessment of cross components and hybrids F1 and F2 for powdery mildew resistance. Determination of chromosome numbers and chromosome configurations in meiosis M1 of F1 plants. Results. Among F2 plants, from the crossing of resistant to powdery mildew introgressive lines of Aurotica and susceptible cultivar Aurora excess of susceptible plants was observed. In order to explain distortion of ratio susceptible : resistant plants in comparison with expected for monogenic segregation, we propose the determined fact of absence in meiosis M1 of MPC of bivalent chromosome conjugation, which results in formation of aneuploid gametes and zygotes with reduced viability. As the third parameter, the one that can influence the mentioned ratio, we propose d parameter, which quantitatively expresses excess of gametes without alien chromatin controlling resistance to powdery mildew. Conclusion. Model of inheritance, which best explains experimental data of F2 plants segregation for resistant and susceptible if the trait is controlled by one dominant gene, takes into account the following conditions for calculation of probabilities of resistant or susceptible plant formation: all female and only euploid male gametes function, nullisomic zygotes are not viable, during meiosis elimination of meiosis products with alien chromatin occurs with parameter d = 0,11–0,12.Received 11.06.2018

Microsporogenesis and meiotic abnormalities in different ‘Oblačinska’ sour cherry (Prunus cerasus L.) clones

The Oblačinska sour cherry (Prunus cerasus) is a mixture of different clones with similar tree and fruit characteristics that is indigenous to and widely planted in commercial orchards in Serbia. Sour cherry, including Oblačinska sour cherry clones, exhibits irregular meiosis which may contribute to low fruit set in some selections. The goal of this study was to examine the process of microsporogenesis and to determine if meiosis and its anomalies effect the in vitro pollen germination and pollen tube length in four ‘Oblačinska’ sour cherry clones that differ in fruit set and yields. All clones displayed varying degrees of chromosomal abnormalities in all meiosis sub-phases. The abnormalities became evident from late pachytene with more than half of the pollen mother cells (PMC) showing abnormal conjugation of chromosomes in metaphase I. The lowest number of PMCs with laggards was in clone III/9 and the highest in clone XIII/1. In second division, the univalent and multivalent association was observed at metaphase-II, the lagging and stickiness in anaphase-II, and the phenomenon persisted up to the microspore stage. In all four ‘Oblačinska’ clones, PMCs exhibited cytomixis phenomena, however, it was only observed in the second experimental year. Cytomixis differed among the four clones but was equally frequent in all stages of meiosis. The syncytia formed, most often consisted of 2–3 PMCs that were at the same phase of meiosis, and exhibited common cytoplasm and occasionally nuclear fusion. In vitro pollen germination and pollen tube length significantly differed between the clones. Most probably abnormalities during meiosis, regardless of the good results of pollen germination, influenced the reduced potential clones XI/3 and XIII/1.

FISH and array CGH characterization of de novo derivative Y chromosome (Yq duplication and partial Yp deletion) in an azoospermic male

This study presents a 28-year-old infertile male who was referred to the cytogenetic laboratory for chromosomal analysis after 4 years of regular unprotected intercourse in whom non-obstructive azoospermia was revealed. Standard cytogenetic G-banding was performed on metaphase spreads and a de-novo karyotype 46,X,der(Y)(q11.22;p11.3) was identified. This analysis was followed by flourescence in-situ hybridization(FISH) and array comparative genomic hybridization (aCGH). Finally, the patient's karyotype was identified as 46,X,der(Y)(qter→q11.221::p11.31→qter).ish der(Y) (qter+,pter-,SHOX+,SRY+,Ycen+,DYZ3+;DYZ1+,qter+).arrYq11.221q12(14,448,863–59,288,511) x2, Yp11.32p11.31(104,062–266,388) x0. It is proposed that de-novo derivative monocentric Y chromosome with duplicated region Y qter→q11.221::p11.31→qter with partial deletion of Yp PAR1 region most probably can perturb the conjugation of sex chromosomes during first meiotic division of spermatogenic arrested differentiation (development).

ЦИТОГЕНЕТИЧЕСКОЕ ИЗУЧЕНИЕ КОЛЛЕКЦИИ СИНТЕТИЧЕСКОЙ ПШЕНИЦЫ ИЗ НАЦИОНАЛЬНОЙ КОЛЛЕКЦИИ ЗЛАКОВ США (NATIONAL SMALL GRAIN COLLECTION OF USDA-ARS) В УСЛОВИЯХ НЕЧЕРНОЗЕМНОЙ ЗОНЫ РОССИИ

CIMMYT collection of synthetic wheats is widely used in breeding programs in many countries due to easy hybridization with domestic varieties, which enhances positive effects in the hybrids. In Russia this collection has never been checked for plant resistance to diseases or used for breeding. We investigated 400 samples of synthetic wheats, obtained in 2009 from National Small Grains Collection (NSGC USDA-ARS, Idaho, USA) to be tested in Nechernozemnaya zone of Russia under brown rust and mildew infection. During 2 years the high-yielding samples were found which were resistant to brown rust, to mildew, and to both pathogens. Nevertheless, the plant response to brown rust attack differed, and the segregation was observed on morphological parameters of ears, leaves and stems. To elucidate why the instability appears, the chromosome conjugation in meiosis was examined and a meiotic index was calculated in 71 synthetic wheats. It was shown that only 63 % of the samples were cytogenetically stable. In the remaining samples the chromosome number varied from 2 n = 40 to 2 n = 43, and different abnormalities (univalents and multivalents) were observed in meiotic metaphase I. Usually in these plants the meiotic index was lower. It is concluded that in the collection a genetic stabilization is still continuing by the appearance of aneuploids. For further genetic and breeding investigations, there are selected the forms with stable cytogenetic parameters, disease resistance and good yielding components (weight per 1000 kernels up to 56 g, and grain yield per ear up to 2.5 g).

The diversity of lifecycles and their role in the evolution of basic chromosome numbers in various living species

Basic chromosome numbers (BCNs) are compared among species with different life-cycle types belonging to four divisions of Gymnospermae, three families of Angiospermae, and three Mammalia subclasses. The gymnosperm and angiosperm taxa that are characterized by alternation of haploid and diploid phases, sporic meiotic reduction, hermaphroditism, and sporophyte dominance have small BCNs: x = 7 to 14. Most of their species are polyploids. Broad BCN variation is observed among species of various mammal subclasses, with sporophyte dominance, gametic meiotic reduction, and the chromosomal sex-determination system. Monotremata species have small BCNs and the ploidy level 10x. In marsupials, BCNs vary from x = 5 to 16, and in Euarchontoglires (placentals), from x = 3 to 51. No polyploids have been found among marsupials or placentals. Chromosome banding and various kinds of fluorescence hybridization of chromosome-specific probes provide evidence that BCN evolution in angiosperms was accompanied by repeated crosses and polyploidization of species with few chromosomes followed by dysploidization by means of conjugation of nonhomologous chromosomes and reciprocal translocations. It is believed that the BCN of the placental ancestor was x = 40–50; of the marsupial ancestor, 16–20; and of the ancestor of monotreme mammals, 5–6. The significant variation among BCNs of the ancestors of the three mammal subclasses, which diverged tens of millions of years ago, suggests that the evolution of BCNs in the ancestors of marsupials and placentals involved polyploidy followed by dysploidy. The species that were analyzed demonstrate a correlation between lifecycle type and BCN range. The results indicate that the genetic difference in sex determination systems was the main cause of BCN variation in the analyzed species, which differ in lifecycle type. The durations of the haploid and diploid phases were of minor significance.

Viruses as triggers of DNA rearrangements in host plants

Andronic, L. 2012. Viruses as triggers of DNA rearrangements in host plants. Can. J. Plant Sci. 92: 1083–1091. Assessment of microsporogenesis in tomato (Lycopersicon esculentum, cultivars Fachel, Nistru and Prizior) infected with tomato aspermy virus or potato virus X and barley (Hordeum vulgare L., cultivars Galactic, Sonor, Unirea) infected with barley stripe mosaic virus showed deviations in the conjugation of homologous chromosomes and segregation of genetic material, expressed in the disruption of chromatin cohesion between homologous chromosomes. The evidence of meiotic division in targeted genotypes indicates the effect of viral infection on chiasmata number and position, promoting the redistribution of chiasmata. On the basis of cytological study, significant changes and the induction of additional exchanges offset by asynapsis were established in early diakinesis. Different parameters, determined at particular stages of meiosis, such as chromosome aberration and the mean percentage of abnormal pollen mother cells, served as cytogenetic evaluation of microsporogenesis in virus-infected tomato or barley cultivars. The study of meiotic stability in anaphase and telophase I and II revealed a significant increase in different types of abnormalities: elimination or/and lagging chromosomes, formation of chromosome and chromatid bridges with or without fragments. Reviewed examples provide data regarding genetic rearrangements in host plants as a response to viral infection.

Genetic and cytological analyses of the male sterility mutation induced in a sorghum tissue culture with streptomycin

Treatment of sorghum callus cultures with 500-1000 mg/l streptomycin led to a high regeneration frequency of plants with complete or partial male sterility (MS), up to 100% of all green regenerants. The induced MS mutation (ms-str) was preserved in the F1 and BC1 progenies and was genetically unstable: many families produced semisterile and fertile revertants, whose progenies again contained semisterile and sterile mutants. The ms-str mutation was maintained through eight generations via selection and self-pollination of semisterile plants. The mutation was inherited as a recessive nuclear mutation in tester crosses of sterile plants segregated in the progenies of fertile and semisterile revertants and was expressed only in single cases in a test cross for ms-str transfer through pollen of hybrids with restored male fertility. Recessive nuclear mutations determining a low plant height (dwarfness) and the lack of waxy bloom on the stem and leaves (bloomless) were found in male-sterile plants with the ms-str mutation. Cytological analysis of sterile plants reveal multiple alterations of various pollen development stages and tapetal cells: cytomyxis, defects of chromosome conjugation, distorted cytokinesis in meiotic division II, a lack of tetrad separation, a defective formation of the microspore coat, generation of microspores with two to four nuclei, and the formation of micronuclei and large vacuoles in tapetal cells. A possible transfer of the induced cytoplasmic MS mutation into the nuclear genome and the causes of the high genetic instability are discussed.

RAPD and Cytomorphological Analyses of F1, F2 and Amphidiploid (A1) Generations of Gossypium arboreum×Gossypium capitis-viridis

The wild diploid species Gossypium capitis-viridis Mauer (2n=2x=26 B4B4) of Cape Verde Islands possess good fibre quality in addition to resistance to pest and diseases. Its narrow bracts ensure clean picking in cultivated cotton. An attempt was made to cross Gossypium arboreum var. MPKV GMS with Gossypium capitis viridis and doubled its chromosomes. The Chromosomes constitution of parents, F1, F2 and amphidiploid was confirmed. The hybridity of cross was confirmed on the basis of cytomorphological studies, pollen test and RAPD analysis. Cytological studies revealed that interspecific hybrid showed anomalous behavior of univalent and the formation of a single and double chromatin bridges at metaphase II that led to abnormal microspore formation in F1 and reduction in fertility. On an average chromosome association at metaphase were 0.976I+10.138II+0.06III+1.142IV and 0.84I+10.549II+0.053III+0.976IV in F1 and F2 of G. arbore-um×G. capitis-viridis, respectively. However, in amphidiploid generation mean chromosome conjugation formed were 0.832I+21.253II+0.05III+2.128IV. Random Amplified Polymorphic DNA (RAPD) analysis was employed to characterize the F1 interspecific hybrid of G. arboreum GMS×G. capitis-viridis, the doubled offspring and six segregants (designated 1–6). The 19 primers, selected from 43 initially screened, generated 250 amplification products of which 232 (92.8%) amplicons were polymorphic. Statistical analysis was carried out using NTSYS-pc software and a dendogram was generated using Jaccard's similarity coefficients. The values for similarity ranged from 0.31 to 0.66. Cluster analysis showed 3 main clusters. Cluster I consists of G. arboreum GMS, segregant 1, 2 and 4; cluster II comprises of G. arboreum GMS×G. capitis-viridis F1 and doubled offspring, segregant 5 and segregant 6 and cluster III consists of segregant 3 and G. capitis-viridis.

Cytology and mendelism: early connection between Michael F. Guyer's contribution.

This paper examines the contribution of the PhD dissertation of the American cytologist Michael F. Guyer (1874-1959) to the early establishment (in 1902-1903) of the parallel relationship between cytological chromosome behaviour in meiosis and Mendel's laws. Guyer's suggestions were among the first, which attempted to relate the variation observed in the offspring in hybridisation studies by a coherent cytological chromosome mechanism to meiosis before the rediscovery of Mendel's principles. This suggested for the first time that the chromosome mechanism involved a conjugation of maternal and paternal chromosomes during the synapsis followed by a segregation of parental chromosomes in the final germ cells and a random union of the final germ cells in the fertilization. It shows that this early suggestion was similar to William Austin Cannon's later chromosome proposal attempting to explain Mendel's principles and had some influence on Walter Sutton's cytological suggestion explaining correctly the behaviour of Mendel's particle by 1903.

Repair of DNA double-strand breaks requires two homologous DNA duplexes

DNA repair and cell survival in haploid and its diploid derivative strains of Saccharomyces cerevisiae were studied after 100 krad X-ray irradiation. The cells were in the G1 stage of the cell cycle, where haploid cells had only one copy of genetic material per genome and diploid had two copies. It was found that diploid could repair double-strand breaks in its DNA after 48 hr of liquid holding which was accompanied by a four-fold rise in survival. In contrast a haploid strain failed to repair its DNA and showed no increase in survival after liquid holding. It is concluded that (1) repair of DNA double-strand breaks requires the availability of two homologous DNA duplexes, (2) restoration of cell viability during liquid holding is connected with repair of DNA double-strand breaks and (3) this repair is a slow process possibly associated with slow finding and conjugation of homologous chromosomes.

PROBABLE BASIS OF DIPLOIDIZATION OF BRASSICA JUNCEA COSS

The natural amphidiploid, Brassica juncea, has diploid-like meiotic behaviour. In three duplication-deficiency plants recovered from an interchange heterozygote stock, a large number of chromosomes were involved in multiple associations. It is suggested that this high level of pairing was due to the conjugation of homoeologous chromosomes and that the deficient segment carries a gene (genes) for suppressing such pairing and for maintaining balanced diploid-like behaviour.

Hybrid Plants between Two Races of Vicia amphicarpa having 2n=10 and 2n=14 Chromosomes

l. Karyological and cytogenetical studies were made on the interspecific hyprid between Vicia amphicarpa (called V. cordata) 2n=10 aud V.amphicarpa, true 2n=14 in order to clarify the distribution of the parental chro-mosomes in the hybrid progenies. 2. In V.amphicarpa, true, ta1 the longest subterminal chromosome which possesses a longer short-arm and the ta3 of the long chromosome which possesses a satellite con-nected to the long arm were identified. The ta6 is one of the short subterminal chromoso-mes and the ta7, the shortest submedian chro-mosome, were also identified. In V. amphicarpa (V.cordata), a2 possesses a short arm which is long compared with the other short arms of other chromosomes; a4 is the middle sub-terminal chromosome which has a long sate-1lite conneected to the long arm were the identified characteristic chromosomes. 3. In the F1, the somatic chromosome number was 2n=12, and the a2, a4, ta1, ta3, ta6 and ta7 of parental chrosomes were identified. Almost all external morphological characters of F1 were intermediate but a few other characters closely resembled to those of V.amphicarpa, true. The growth of AR×Ta F1 Plants was superior to that of Aw×Ta F1. The fertility in AR×Ta Fl was consder-ably low and sterile in the Aw×Ta F1. The chromosome conjugation at M(I) of PMCS Was loose compared with those of the other inters-pecific hybrids of V.sativa and its related species, and many univalent and multivalent chromosome conjugations were observed.

Genetic Affinities of the North American Species of Hibiscus Sect. Trionum

Study of herbarium specimens, crossing behavior, chromosome conjugation, and live populations has shown that the endemic North American species ofHibiscus sect.Trionum comprise two distinct genetic groups.Hibiscus militaris Cav. andH. coccineus Walt, crossed readily and yielded fertile Fi’s. Also,H. incanus Wendl.,H. moscheutos L., andH. lasiocarpos Cav. crossed freelyinter se, and the hybrids were all vigorous and fertile. However, crosses of these three forms with eitherH. militaris orH. coccineus gave lethal hybrids. Preliminary evidence suggests thatH. palustris L. is similar toH. moscheutos, H. incanus, andH. lasiocarpos in crossing behavior. These four forms were found to occur in distinct geographical areas. They may be considered as ecotypes of a single ecospecies.H. grandiflorus Michx. is morphologically related to this alliance, but yielded a viable fertile hybrid when crossed withH. coccineus. Further study of the affinities ofH. grandiflorus andH. palustris is in progress.