Detection of interspecific translocations in mouse-human hybrids by alkaline Giemsa staining.

Alkaline Giemsa staining of chromosome preparations from mouse-human somatic cell hybrids has indicated the presence of interspecific translocations previously undetected by conventional banding procedures. The species specificity of the alkaline Giemsa stain has been substantiated by differential color staining of all mouse and human chromosomes and a mouse-human translocation in well characterized hybrid clones.     

The evolutionary implications of interspecific hybridization among four species of zinnia sect. Mendezia (compositae)

Fertile interspecific hybrids were obtained among four species ofZinnia sect.Mendezia. The collection data and the segregation for ray color in F₁ hybrids suggest natural interspecific hybridization. Cytological data suggest that the descent of the four species from a common ancestor was accompanied by reciprocal translocations involving non-homologous chromosomes.     

Nonstructural Chromosome Differentiation among Wheat Cultivars, with Special Reference to Differentiation of Chromosomes in Related Species

Wheat cultivar Chinese Spring (Triticum aestivum L. em. Thell.) was crossed with cultivars Hope, Cheyenne and Timstein. In all three hybrids, the frequencies of pollen mother cells (PMCs) with univalents at metaphase I (MI) were higher than those in the parental cultivars. No multivalents were observed in the hybrids, indicating that the cultivars do not differ by translocations. Thirty-one Chinese Spring telosomic lines were then crossed with substitution lines in which single chromosomes of the three cultivars were substituted for their Chinese Spring homologues. The telosomic lines were also crossed with Chinese Spring. Data were collected on the frequencies (% of PMCs) of pairing of the telesomes with their homologues at MI and the regularity of pairing of the remaining 20 pairs of Chinese Spring chromosomes in the monotelodisomics obtained from these crosses. The reduced MI pairing in the intercultivar hybrids was caused primarily by chromosome differentiation, rather than by specific genes. Because the differentiation involved a large part of the chromosome complement in each hybrid, it was concluded that it could not be caused by structural changes such as inversions or translocations. In each case, the differentiation appeared to be unevenly distributed among the three wheat genomes. It is proposed that the same kind of differentiation, although of greater magnitude, differentiates homoeologous chromosomes and is responsible, together with structural differentiation, for poor chromosome pairing in interspecific hybrids.     

Flower senescence in daylily (Hemerocallis)

This paper reviews recent developments in the use of molecular probes for analyzing the genetic makeup of somatic hybrids. Successful application of somatic hybridization to the interspecific transfer of traits encoded in the nucleus is still having limited success. A major difficulty is hybrid infertility, particularly in hybrids between sexually incompatible species. The formation of asymmetric hybrids is being explored as an approach for improving hybrid fertility. Evaluation of the degree of chromosome elimination and chromosome stability and instability in asymmetric hybrids is difficult when the traditional approaches of chromosome counting and isozyme analysis are used. Two new approaches are resolving this difficulty. The use of species-specific repetitive DNA probes in dot blotting and in situ hybridization to chromosomes is providing quantitative data on chromosome elimination and allows detection of translocations. Use of restriction fragment length polymorphism (RFLP) probes for analysis of hybrids between genetically mapped species makes it possible to account for the presence or absence of individual chromosomes and chromosomes arms. Wider use of such molecular probes should greatly improve our understanding of the genetics of both symmetric and asymmetric somatic hybrids and may lead to new strategies for the effective interspecific transfer of nucleus-encoded traits by protoplast fusion.     

Assignment of the structural gene encoding human aspartylglucosaminidase to the long arm of chromosome 4 (4q21----4qter)

The structural gene for the human lysosomal enzyme aspartylglucosaminidase (AGA) has been assigned to chromosome 4 using somatic cell hybridization techniques. The human monomeric enzyme was detected in Chinese hamster-human cell hybrids by a thermal denaturation assay that selectively inactivated the Chinese hamster isozyme, while the thermostable human enzyme retained activity. Twenty informative hybrid clones, derived from seven independent fusions, were analyzed for the presence of human AGA activity and their human chromosomal constitutions. Without exception, the presence of human AGA in these hybrids was correlated with the presence of human chromosome 4. All other human chromosomes were excluded by discordant segregation of the human enzyme and other chromosomes. Two hybrid clones, with interspecific Chinese hamster-human chromosome translocations involving the long arm of human chromosome 4, permitted the assignment of human AGA to the region 4q21----4qter.     

ADAPTIVE RADIATION IN THE HAWAIIAN SILVERSWORD ALLIANCE (COMPOSITAE-MADIINAE). II. CYTOGENETICS OF ARTIFICIAL AND NATURAL HYBRIDS

The Hawaiian silversword alliance of Argyroxiphium, Dubautia, and Wilkesia, in spite of exhibiting spectacular morphological, ecological, physiological, and chromosomal diversity, is remarkably cohesive, genetically. This is attested to by the ease of production of artificial hybrids and by the high frequency of spontaneous hybridization among such life forms as mat-forming subshrub, monocarpic rosette shrub, polycarpic shrub, cushion plant, tree, and vine. Even the least fertile of these hybrids is capable of producing backcross progeny. Moreover, first generation interspecific and intergeneric hybrids have been successfully used to produce trispecific hybrids in a number of instances. In general, the widest hybrid combinations have been as readily produced as crosses within a species. At present eight genomes or chromosome races distinguished by reciprocal translocations are recognized on the basis of meiotic analysis of artificial and spontaneous hybrids. Seven of these races are found among those species with 14 pairs of chromosomes. The eighth genome very likely characterizes all nine species of this alliance that have 13 pairs of chromosomes. The cytogenetic data indicate that redundancy of translocations involving the same chromosomes has been a recurrent theme in the chromosomal differentiation of these taxa. There appears to be little, if any, correlation between chromosomal evolution and adaptive radiation as assessed by gross habital differentiation in this group. However, within Dubautia, a novel ecophysiological trait associated with colonization of xeric habitats is restricted to species with n = 13. In contrast to the bulk of the Hawaiian flora, which is characterized by self-compatibility and chromosomal stability, it is suggested that the occurrence of self-incompatibility in the Hawaiian Madiinae may have favored selection of supergenes via chromosomal repatterning, and this may account for the diversity of chromosome structure seen in this group.     

Molecular and cytological analyses of A and C genomes at meiosis in synthetic allotriploid <Emphasis Type="Italic">Brassica</Emphasis> hybrids (ACC) between <Emphasis Type="Italic">B.napus</Emphasis> (AACC) and <Emphasis Type="Italic">B.oleracea</Emphasis> (CC)

Success of interspecific hybridization relies mostly on the adequate similarity between the implicated genomes to ensure synapsis, pairing and recombination between appropriate chromosomes during meiosis in allopolyploid species. Allotetraploid Brassica napus (AACC) is a model of natural hybridization between Brassica rapa (AA) and Brassica oleracea (CC), which are originally derived from a common ancestor, but genomic constitution of the same chromosomes probably varied among these species through time after establishment, giving rise to cytogenetic difference in the synthetic hybrids. Herein we investigated meiotic behaviors of A and C chromosomes of synthetic allotriploid Brassica hybrids (ACC) at molecular and cytological levels, which result from the interspecific cross between natural B. napus (AACC) and B.oleracea (CC), and the results showed that meiosis course was significantly aberrant in allotriploid Brassica hybrids, and chromosomes aligned chaotically at metaphase I, chromosome bridges and lags were frequently observed from later metaphase I to anaphase II during meiosis. Simultaneously, we also noticed that meiosis-related genes were abruptly down-regulated in allotriploid Brassica hybrids, which likely accounted for irregular scenario of meiosis observed in these synthetic hybrids. Therefore, these results indicated that inter-genomic exchanges of A and C chromosomes could occur frequently in synthetic Brassica hybrids, and provided an efficient approach for genetic changes of homeologous chromosomes during meiosis in polyploid B.napus breeding program.     

Polyploid formation pathways have an impact on genetic rearrangements in resynthesized Brassica napus

? Polyploids can be produced by the union of unreduced gametes or through somatic doubling of F(1) interspecific hybrids. The first route is suspected to produce allopolyploid species under natural conditions, whereas experimental data have only been thoroughly gathered for the latter. ? We analyzed the meiotic behavior of an F(1) interspecific hybrid (by crossing Brassica oleracea and B.rapa, progenitors of B.napus) and the extent to which recombined homoeologous chromosomes were transmitted to its progeny. These results were then compared with results obtained for a plant generated by somatic doubling of this F? hybrid (CD.S?) and an amphidiploid (UG.S?) formed via a pathway involving unreduced gametes; we studied the impact of this method of polyploid formation on subsequent generations. ? This study revealed that meiosis of the F? interspecific hybrid generated more gametes with recombined chromosomes than did meiosis of the plant produced by somatic doubling, although the size of these translocations was smaller. In the progeny of the UG.S? plant, there was an unexpected increase in the frequency at which the C1 chromosome was replaced by the A1 chromosome. ? We conclude that polyploid formation pathways differ in their genetic outcome. Our study opens up perspectives for the understanding of polyploid origins.     

Genetic differentiation in theAedes atropalpus complex. II. Chromosomal divergence betweenAe. atropalpus andAe. epactius

Analysis of meiotic chromosomes from hybrids betweenAedes atropalpus andAe. epactius has revealed that the two species are fixed for alternate arrangements of four inversions: a paracentric inversion of chromosome 1, two paracentric inversions of chromosome 2, and a pericentric inversion of chromosome 3. This chromosomal heterozygosity in the interspecific hybrids has resulted in extensive meiolic chromosomal asynapsis. Dicentric bridges, acentric fragments, and chromosomal breakage were also associated with the heterozygous inversions. This disruption of meiosis was sufficient to account for the partial sterility observed in interspecific hybrids. No chromosomal polymorphisms, aberrations, or reduction in fertility was observed in parental strains of intraspecific hybrids of the two species.     

八倍体小黑麦×普通小麦杂种后代群体中的染色体易位

用改良的Giemsa C-带技术以单株为基础分析了八倍体小黑麦×普通小麦的杂种BC_1,F_(?)和F_(?)代植株的核型。在鉴定了C-带核型的1098株杂种后代植株中,发现了78条小麦-黑麦和277条黑麦-黑麦易位染色体。在不同的世代和株系中,小麦-黑麦染色体易位率变化在4.35—14.07%之间,平均7.10%;黑麦-黑麦染色体易位率在0.48—52.78%之间,平均25.23%。鉴定的小麦-黑麦易位染色体涉及了黑麦的14条不同的染色体臂和小麦的A、B和D组染色体。易位的48.57%发生在小麦和黑麦的部分同源染色体之间,51.43%发生在非部分同源染色体之间。不同的黑麦染色体臂参与易位的频率不同。小麦-黑麦染色体易位主要发生在杂种的早期世代,使用适当的选择技术在F_3获得了纯合的易位植株。文中讨论了快速选育易位系的技术和它们在小麦育种中的应用问题。     

Genome discrimination in progeny of interspecific hybrids between Brassica napus and Raphanus raphanistrum.

Genomic in situ hybridization (GISH) applied to the F1 interspecific hybrid between oilseed rape (Brassica napus, AACC, 2n = 38) and wild radish (Raphanus raphanistrum, RrRr, 2n = 18) showed the predicted 19 chromosomes from B. napus and 9 chromosomes from R. raphanistrum. The very low female fertility of these interspecific hybrids when backcrossed to R. raphanistrum led to only two descendants. Their chromosome number varied between 45 and 48. Both of these progenies showed only 9 chromosomes from R. raphanistrum and 36-39 chromosomes from B. napus. These results indicate the efficiency and limits of GISH as a suitable tool to assess and interpret the behavior of chromosomes after such interspecific crosses. The unexpected chromosome combination is discussed.     

Uniparental chromosome elimination in the early embryogenesis of the inviable salmonid hybrids between masu salmon female and rainbow trout male

Chromosome elimination through chromosome loss and partial deletion is known to be one of the causes of embryonic inviability in some salmonid interspecific hybrids. Using fluorescence in situ hybridization and related techniques, including whole chromosome painting and comparative genomic hybridization, parental origin of eliminated chromosomes was identified in the inviable hybrids between masu salmon (Ms, Oncorhynchus masou) female and rainbow trout (Rb, O. mykiss) male at the early embryonic stage prior to death. In these hybrids, the haploid Rb chromosome number decreased to nearly half, whereas the Ms chromosomes were retained as one or occasionally two full haploid complements. The Rb chromosomes were also involved in the frequently observed fragments and micronuclei. Whereas the occurrence of fragments was constant throughout the observed period, chromosome loss occurred mainly from just after fertilization to the blastulae stage. In tissue sections and cell spreads of late blastula, some Rb chromosomes were trapped in the midzone from ana- to telophase, resulting in micronuclei at the subsequent interphase. Micronuclei and mitotic abnormalities were also observed in the androgenetic haploid hybrids. However, such abnormalities were seldom or never observed in the viable reciprocal hybrids. The present findings suggest that the paternal Rb chromosomes in the inviable hybrids are preferentially eliminated through mitotic abnormalities during early embryogenesis, owing to a possible incompatibility between the maternal Ms cytoplasm and paternal Rb genome. Received: 22 August 1996; in revised form: 14 November 1996 / Accepted: 20 November 1996     

SYNTHETIC HYBRIDS OF NEW WORLD AND OLD WORLD AGROPYRONS. I. TETRAPLOID AGROPYRON SPICATUM × DIPLOID AGROPYRON CRISTATUM

Four interspecific hybrids of tetraploid A. spicatum × diploid A. cristatum ‘Fairway’ were obtained by controlled pollinations of emasculated and unemasculated spikes of A. spicatum. Most vegetative and spike characteristics of the hybrids were intermediate between those of the parent species. Tetraploid A. spicatum behaved cytologically as an autotetraploid, with mean chromosome associations of 0.09 I, 7.95 II, 0.03 III, and 2.98 IV being observed in 103 cells interpreted. The diploid A. cristatum was cytologically regular and formed 7 bivalents in 160 of 163 cells examined. Meiosis in the triploid hybrids was highly irregular, and these plants were completely sterile. Chromosomes of A. spicatum and A. cristatum differed sufficiently in size so that they could be distinguished in the hybrids. Seven bivalents and 7 univalents were formed in 90.5% of 262 cells interpreted at metaphase I. Mean chromosome associations of 6.87 I, 6.98 II, and 0.05 III were observed in the hybrids. Most chromosome pairing was due to autosyndesis of A. spicatum chromosomes, but A. cristatum chromosomes occasionally paired among themselves and with A. spicatum chromosomes. Tetraploid A. spicatum was considered to be an autotetraploid. On the basis of cytological evidence, A. cristatum, A. spicatum, and their interspecific hybrids were represented by genome formulae of AA, BBBB, and ABB, respectively.     

Sexually differentiated mechanisms of sterility in interspecific hybrids between Oryzias latipes and O. curvinotus.

Fertility of interspecific hybrids between Oryzias latipes and O. curvinotus was examined. F1 females were able to lay eggs but males were sterile. Histological examination of the ovaries of hybrids revealed that oogenesis does not proceed normally in spite of the apparent fertility. Most oocytes degenerated at the pachytene stage of the meiotic prophase, and only a few entered the diplotene stage to develop into ova. Hybrid males could induce females to spawn eggs, an indication that they had differentiated completely into true males. However, they did not produce fertile sperm. Most germ cells in testes of hybrids passes through almost the entire process of spermatogenesis, but deviations from the normal course of events were observed during spermiogenesis. The condensation of chromatin in spermatids occurred, but the diameters of sperm heads were about 1.5-fold larger than those of normal ones. Prominent abnormalities were apparent in the quantity and arrangement of microtubules in the cytoplasm. Abnormal spermatozoa were phagocytized by Sertoli cells. These observations indicate that the mechanisms of impaired gametogenesis in these interspecific hybrids are sexually differentiated.     

Construction and analysis of linking libraries from the mouse X chromosome

A hybrid cell line containing the mouse X chromosome on a human background has been used to construct linking libraries from the mouse X chromosome, and approximately 250 unique EagI and NotI clones have been identified. Seventy-three clones have been sublocalized onto the X chromosome using interspecific Mus spretus/Mus domesticus crosses and a panel of somatic cell hybrids carrying one-half of reciprocal X-autosome translocations. The average spacing of the linking clones mapped to date is about one every 2 Mb of DNA. Two clones from the central region of the chromosome have been physically linked by pulsed-field gel electrophoresis. A large number of clones contain conserved sequences, indicating the presence of CpG-rich island-associated genes. The clones isolated from these libraries provide a valuable resource for comparative mapping between man and mouse X chromosomes, isolation of X-linked disease loci of interest by reverse genetics, and analysis of the long-range structure and organization of the chromosome.     

Chromosome and nucleotide sequence differentiation in genomes of polyploid Triticum species

Summary The nature of genome change during polyploid evolution was studied by analysing selected species within the tribe Triticeae. The levels of genome changes examined included structural alterations (translocations, inversions), heterochromatinization, and nucleotide sequence change in the rDNA regions. These analyses provided data for evaluating models of genome evolution in polyploids in the genus Triticum, postulated on the basis of chromosome pairing at metaphase I in interspecies hybrids.The significance of structural chromosome alterations with respect to reduced MI chromosome pairing in interspecific hybrids was assayed by determining the incidence of heterozygosity for translocations and paracentric inversions in the A and B genomes of T. timopheevii ssp. araraticum (referred to as T. araraticum) represented by two lines, 1760 and 2541, and T. aestivum cv. Chinese Spring. Line 1760 differed from Chinese Spring by translocations in chromosomes 1A, 3A, 4A, 6A, 7A, 3B, 4B, 7B and possibly 2B. Line 2541 differed from Chinese Spring by translocations in chromosomes 3A, 6A, 6B and possibly 2B. Line 1760 also differed from Chinese Spring by paracentric inversions in arms 1AL and 4AL whereas line 2541 differed by inversions in 1BL and 4AL (not all chromosomes arms were assayed). The incidence of structural changes in the A and B genomes did not coincide with the more extensive differentiation of the B genomes relative to the A genomes as reflected by chromosome pairing studies.To assay changing degrees of heterochromatinization among species of the genus Triticum, all the diploid and polyploid species were C-banded. No general agreement was observed between the amount of heterochromatin and the ability of the respective chromosomes to pair with chromosomes of the ancestral species. Marked changes in the amount of heterochromatin were found to have occurred during the evolution of some of the polyploids.The analysis of the rDNA region provided evidence for rapid fixation of new repeated sequences at two levels, namely, among the 130 bp repeated sequences of the spacer and at the level of the repeated arrays of the 9 kb rDNA units. These occurred both within a given rDNA region and between rDNA regions on nonhomologous chromosomes. The levels of change in the rDNA regions provided good precedent for expecting extensive nucleotide sequence changes associated with differentiation of Triticum genomes and these processes are argued to be the principal cause of genome differentiation as revealed by chromosome pairing studies.     

Predominant loss of hamster chromosomes in hybrids of somatic cells from the Dzungarian hamster and mice]

By means of the application of UV-inactivated Sendai virus interspecific hybrids of Dzungarian hamsterXmouse somatic cells were obtained in HAT selective medium. Karyotypic changes in these hybrid somatic cells were recorded during a 13 months' period. In the beginning each hybrid somatic cell contained 1 chromosome set of Dzungarian hamster and 1 mouse chromosome set. It was observed that throughout 13 months' of cultivation the elimination of Dzungarian hamster chromosomes prevailed over that of mouse chromosomes.     

The evolutionary history of Drosophila buzzatii XI. A new method for cytogenetic localization based on asynapsis of polytene chromosomes in interspecific hybrids of Drosophila

A new method for mapping gene differences between species is introduced. It is based on the asynapsis of homologous chromosomes in interspecific hybrids. Its validity has been investigated by comparing the pairing patterns of two Drosophila species and their hybrids, and by localizing on the chromosomes several diagnostic allozyme loci. The method can be used to map the genetic basis of any character exhibiting differences between species, although these species must fulfill some important conditions for the method to be applied with maximum efficiency.     

Comparative study ofTriticum aestivum andT. timopheevi genomes using C-banding technique

The somatic chromosomes ofTriticum timopheevi and those of two varieties ofT. aestivum, Chinese Spring and Bezostaya-1, have been identified by a Giemsa staining technique. The data suggest thatT. timopheevi and tetraploid wheats had a common ancestor from which their genomes differentiated due to chromosomal aberrations and the increase of heterochromatin in the chromosomes of theT. timopheevi G-genome. The differences between the chromosomes of the AB and AG genomes result in substitutions and large translocations between these chromosomes in interspecific hybrids.     

Chromosome mapping of the murine syndecan gene.

The chromosomal localization of the murine syndecan gene was determined by analysis of DNA from a panel of mouse-hamster cell hybrids containing various mouse chromosomes, detection of immunoreactive syndecan in culture medium of these cells, and linkage analysis of a mouse interspecific backcross. Southern analysis of the mouse-hamster cell hybrid DNA shows two distinct hybridizing sequences, one on mouse Chromosome 12 and the other on the X chromosome. Localization of the syndecan gene to mouse Chromosome 12 was determined by detection of immunoreactive syndecan in the culture medium of cell hybrids containing mouse Chromosome 12. Hybrids containing other mouse chromosomes were negative. Linkage analysis by Southern hybridization of DNA from a mouse interspecific backcross using a syndecan-specific probe localized the syndecan gene locus, Synd, to the proximal end of Chromosome 12, tightly linked to the Pomc-1 and Nmyc loci. The syndecan gene is likely on human Chromosome 2 because this region shows conservation of synteny between mouse and human chromosomes.