Differential Giemsa staining of heterochromatic B-chromosomes in Myrmeleotettix maculatus (Thunb.) (Orthoptera: Acrididae)

A modified Giemsa staining technique has been used to investigate the karyotype of the grasshopper Myrmeleotettix maculatus, since this stain appears to be diagnostic for certain repetitive DNAs. The centromeric regions are densely heterochromatic, and further heterochromatic bands occur on the X-chromosome and on both arms of the B-chromosome. The significance of these results is discussed in relation to centromeric structure and B-chromosome structure in this insect, and a possible origin of the B-chromosome is suggested.     

The nature and behaviour of supernumerary chromosomes in the rhizirideum group of the genus Allium

Individuals at various levels of ploidy in three species of Allium (angulosum, nutans and senescens) contain a morphologically uniform B-chromosome. This supernumerary is different in character from other B-types recorded for the genus. In diploids the B divides at second anaphase so that 50% of the pollen grains transmit it. The level of transmission is lower in the pollen of polyploids and still lower on the female side where pre-meiotic elimination occurs in both diploids and polyploids. Despite this, and although no effect of the B could be discerned on germination, all plants examined possessed the B-chromosome.This paper was prepared in the Department of Genetics, University of Birmingham while the author was a recipient of a British Council Scholarship.     

Influence of a rare unstable B-chromosome on chiasma frequency and nonhaploid sperm production in Dichroplus pratensis (Melanoplinae,Acrididae)

Three B-containing individuals of Dichroplus pratensis were found among 300 males collected in several Argentine localities. The B-chromosome is a partially euchromatic short telocentric and it is mitotically unstable. The B-chromosome number of testis cells ranged from 0 to 4 in two males and from 0 to 3 in the remaining one; this variation was inter- as well as intrafollicular. Meiotic behaviour of the Bs was very regular, association of Bs was usually chiasmate and no lagging univalents were observed during first division. The presence of Bs increased the production rate of abnormal spermatids and this effect was more pronounced in follicles with odd numbers of Bs. Chiasma frequency and between-cell variance were also increased in B-containing cells. A possible interaction between the Bs and the polymorphic centric fusions present in the species is discussed in relation to chiasma frequency determination.     

The B-chromosome in the karyotype of Tetrix tenuicornis (Sahlb.) (Tetrigidae: Orthoptera)

B-chromosomes were observed in a Polish natural population of Tetrix tenuicornis. Three males showed a mitotically unstable and probably acrocentric B-chromosome, similar in size to the sex chromosome. In one specimen two forms of the B-chromosome occurred in various combinations (i.e. 6A+X; 6A+B; A; 6A+X+B; 6A+X+2B).     

The relationship of abnormal chromosome 10 to B-chromosomes in maize

Abnormal chromosome 10 (K10) is known to increase recombination in maize and to induce preferential segregation in knobbed heterozygotes during megasporogenesis. In spite of the considerable interest generated by these findings, the origin of the K10 chromosome is unknown. It has been postulated that the extra segment of K10 arose by simple translocation between normal 10 and a B-chromosome. This hypothesis was tested by comparing meiosis in haploids with either K10 or the normal 10 and carrying a single B-chromosome. The frequency of bivalent configurations was found to be similar in the two types of haploids suggesting that the K10 and B-chromosomes do not share homologies that lead to chiasma formation. These results lend no support to the hypothesis that the K10 chromosome came from a B type. The implications of these results to the action of K10 at meiosis are also discussed.     

Interpopulation variation in the satellite DNA from grasshoppers with B-chromosomes

When run on a CsCl gradient the DNA from individuals containing B-chromosomes reveals a satellite peak in addition to the main DNA peak found in individuals without B-chromosomes. This was shown in several populations of grasshoppers. This B-chromosome DNA contains 28% repeated and 72% unique sequences as determined by hydroxyapatite chromatography. This was shown to be the case in two of the populations. The really surprising observation was that the repeated nucleotide sequences of the B-chromosome DNA have no apparent homology in this single species of grasshopper. This was demonstrated by the lack of hybridisation between labelled C-RNA transcribed from one B-chromosome DNA and the DNA from the B-chromosome peak from another population. This lack of homology was also suggested by density differences between B-chromosome satellites in CsCl gradients. Furthermore, there was no sequence homology between the satellite (B-chromosome) DNA and the main peak (nuclear) DNA.     

B-Chromosomen beiChironomus

In the population “Herrenmühle” ofChironomus plumosus 11% of the individuals contain one supernumerary chromosome. This B-chromosome is present both in germ-line and somatic cells. — InChironomus melanotus 6% of the larvae of the population “Falkau” carry supernumerary chromosomes. These B-chromosomes cannot be found in all nuclei of testis and soma, their number varies between cells within the individual. In both species the B-chromosomes represent centromeric fragments of chromosome IV as can be shown by their structure and pairing behaviour. — The polytene B-chromosome ofCh. plumosus exhibits a banding pattern in the salivary gland nuclei. Furthermore it is able to form an additional nucleolus in the nuclei of the malpighian tubules. InCh. melanotus band structures can be seen only in the B-chromosome of malpighian tubules. The larvae ofCh. melanotus, carrying B-chromosomes, show heterochromatic bodies in the salivary gland nuclei, varying in number and size in the nuclei of the same gland. These bodies are interpreted to be polytenic B-chromosomes divided into subunits.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Origin and molecular organization of supernumerary chromosomes of Prochilodus lineatus (Characiformes, Prochilodontidae) obtained by DNA probes

In Prochilodus lineatus B-chromosomes are visualized as reduced size extra elements identified as microchromosomes and are variable in morphology and number. We describe the specific total probe (B-chromosome probe) in P. lineatus obtained by chromosome microdissection and a whole genomic probe (genomic probe) from an individual without B-chromosome. The specific B-chromosome was scraped and processed to obtain DNA with amplification by DOP-PCR, and so did the genomic probe DNA. Fluorescence in situ hybridization using the B-chromosome probe labeled with dUTP-Tetramethyl-rhodamine and the genomic probe labeled with digoxigenin-FITC permitted to establish that in this species supernumerary chromosomes with varying number and morphology had different structure of chromatin when compared to that of the regular chromosomes or A complement, since only these extra elements were labeled in the metaphases. The present findings suggest that modifications in the chromatin structure of B-chromosomes to differentiate them from the A chromosomes could occur along their dispersion in the individuals of the population.     

滇韭的B-染色体及抗逆生理特性研究初探

对B-染色体在滇韭二倍体和四倍体中的分布进行了调查,并测定了不同海拔高度二倍体植株的抗氧化酶系活力、丙二醛和脯氨酸的含量,探索B-染色体对滇韭形态、育性及抗逆性的影响。结果表明：B-染色体在二倍体和四倍体滇韭中的分布和数量存在较大差异;B-染色体的存在对二倍体滇韭的形态和育性具有明显影响;SOD酶活及MDA含量与海拔高度呈一定的相关性。     

Phyletic hot spots for B chromosomes in angiosperms

We determined whether supernumerary B chromosomes were nonrandomly distributed among major angiosperm lineages and among lineages within families, as well as the identity of lineages with unusually high B-chromosome frequencies (hot spots). The incidence of B chromosomes for each taxon was gathered from databases showing species with and without these chromosomes (among species with known chromosome numbers). Heterogeneity was found at all ranks above the species level. About 8% of monocots had B chromosomes versus 3% for eudicots; they were rare in nonmonocot basal angiosperms. Significant heterogeneity in B-chromosome frequency occurred among related orders, families within orders, and major taxa within families. There were many B-chromosome hot spots, including Liliales and Commelinales at the order level. At the family level, there was a trend suggesting that B-chromosome frequencies are positively correlated with genome size.     

Stability of the population variants of the B-chromosome system in the East-Asian mouse Apodemus peninsulae from the Baikal region and Northern Mongolia

Analysis of the B-chromosome frequency and morphotypes in 160 mice Apodemus peninsulae from 17 localities of the Baikal region, Northern Mongolia, Trans-Baikalia, and the Russian Far East showed that the mice were from five geographical populations. The interpopulation difference was determined by variations of 0?C4 macro B chromosomes and 0?C11 micro B chromosomes. The B-chromosome number and morphotypes proved to be stable over the past 30 years in the geographical populations under study.     

Population cytology of the genus Phaulacridium

Samples were taken from twenty three Australian mainland populations of the shorthorned grasshopper, Phaulacridium vittatum. Five of these populations were found to be polymorphic for B-chromosomes. The anaphase I segregation of the B-chromosome appeared to be random with respect to the X (contra Jackson and Cheung, 1967). The B-chromosomes did not appear to influence chiasma frequency in the population in which they were found.     

Molecular-cytogenetic characteristics of B-chromosomes in chironomid (Diptera, Chironomidae)

Morphological and molecular study of B-chromosomes of three Chironomus species (siblings Ch. borokensis and Ch. phumosus from plumosus group, and Ch. heterodentatus from obtusidens group) was carried out. Morphological similarity of B-chromosome banding pattern and telomer-centromeric region banding pattern of chromosome IV in Ch. borokensis was shown. Polytene B-chromosomes of Ch. borokensis and Ch. heterodentatus were microdissected, and their DNA was amplified using degenerate oligonucleotide primer polymerase chain reaction. Comparative analysis of the localization of homologous B-chromosome DNA sequences of A- and B-polytene chromosomes was made using in situ fluorescence hybridization. It has been shown that B-chromosomes in the studied species are composed mainly of repetitive DNA sequences homologous to sequences of centromeric and telomeric DNA of A-chromosomes, and also these of the mobile element NLRCthl. The B-chromosome DNA, homologous to sequences of DNA mobile element, was scattered on A-chromosomes (more than 100 sites). No ribosomal DNA repeats were identified in B-chromosome. Heterologous FISH of B-chromosome DNA to polytene A-chromosomes of Ch. thummi, a species lacking B-chromosomes, enabled us to reveal the presence of numerous sites homologous to DNA of B-chromosomes. These are mainly mobile element sites. An origin of B-chromosomes and peculiarities of their organization in chironomids are discussed.     

Segregation-distortion in the B-chromosome system ofTettigidea lateralis (say) (Orthoptera: Tetrigidae)

A marginal population ofTettigidea lateralis was found to be polymorphic with respect to a large, mitotically stable supernumerary (B) chromosome. Male and female individuals may carry one or two B-chromosomes. In the male sex the frequency of individuals with one B was 33.8% whereas that of 2B-carriers was 2.9 %. A comparison with a small sample of female individuals suggests similar frequencies of B-chromosome carriers in the two sexes. The pycnocity cycle of the B's is virtually identical to that of the X chromosome which is always distinguishable by virtue of its larger size and other structural details. Persistent heterochromatic associations between the B and the X, which may last until metaphaseanaphase I, lead to a preferential migration of the B with the X to the same pole in male carriers of a single supernumerary. This distortional segregation of the B-chromosome may produce a differential transmission of the supernumerary to the two sexes if the various types of gametes are equally functional. Achiasmate, persistent B-B associations in 2B individuals can also cause segregation-distortion. The two supernumeraries segregate to the same pole in approximately 1/3 of the spermatocytes, but their poleward movement relative to that of the X is random. Both –B and +B individuals show only a single chiasma per individual bivalent. However, the presence of a single B raises very significantly the frequency at which the chiasma forms at the extreme distal ends of the L₁-L₂ and M₃-M₄ autosomes. The effect on recombination exerted by the supernumeraries and the possible implications of the segregation-distortion system ofT. lateralis are discussed in the light of recent studies on comparable B-chromosome polymorphisms.Research supported by N.R.C. of Canada.     

A cytogenetic analysis in Psophus stridulus (L.) (Orthoptera: Acrididae): B-chromosomes and abnormal spermatid nuclei

The male chromosome complement of Psophus stridulus (L.) (Orthoptera: Acrididae) has been analyzed by using orcein staining, C-banding and silver impregnation. During spermatogenesis only one pair of autosomes (M₉) shows an active nucleolar organizer region located in a C-banded constriction. There are other chromosome pairs with constrictions but these do not show nucleolar activity. The relationship between these constrictions and the C-banding pattern exhibited by this species is analyzed.In a sample of 83 males from five populations, two different supernumerary chromosomes were observed. Four males had a metacentric B-chromosome (B^m) similar in size to the sex chromosome and mitotically stable. Its meiotic behaviour indicates that it is an isochromosome. An additional small B-chromosome (B⁸) was also found in a single follicle of one individual carrying the B^m.A high rate of abnormal spermatids (macrospermatids) was scored in the individuals carrying B's. This proportion is notably higher in the follicle containing both the B^m and the B⁸.     

Isolation of a sequence common to A- and B-chromosomes of rye (Secale cereale) by microcloning

The techniques of microdissection and microcloning have been applied to the isolation of B-chromosome DNA from rye. We have identified a DNA sequence on the rye B-chromosome which is homologous to an A-chromosome sequence, and which is dispersed and moderately repeated on the A- and B-chromosomes. This demonstrates that the rye B-chromosome is heterogeneous in the nature of its DNA sequence composition, containing sequences which are present on the A-chromosomes in addition to those not present on the A-chromosomes.     

THE ASSOCIATION OF A SINGLE B-CHROMOSOME WITH MALE STERILITY IN PLANTAGO CORONOPUS

Paliwal , Ripsudan L. (B. R. College, Agra, India.), and Beal B. Hyde . The association of a single B-chromosome with male sterility in Plantago coronopus. Amer. Jour. Bot. 46(6): 460–466. Illus. 1959.—Two species of Plantago showing male sterility have been studied cytogenetically. In P. ovata (n=4) the sterility appears to be cytoplasmic. In P. coronopus (n=5) all male-sterile plants contain a single extra chromosome which is largely heterochromatic, shorter, and not homologous with any of the other chromosomes. No male-fertile plants contain this B-chromosome. Meiosis is regular in the male-sterile lines. The accessory chromosome usually does not divide and moves to one pole at the first division of meiosis and divides regularly in the second division. Degeneration of all microspores occurs before pollen mitosis. Male-sterile plants are apomictic, but whether or not male-fertile plants are also apomictic has not yet been determined.     

B-Chromosomes and E-1 isozyme activity in mosaic bulbs of Scilla autumnalis (Liliaceae)

The electrophoretic patterns of esterase (E-1), alcohol dehydrogenase (ADH), and glutamate oxaloacetate transaminase (GOT) isozymes were studied in two Spanish populations of the lily Scilla autumnalis with B-chromosome carrying individuals. The E-1 isozyme activity appears only in those individuals with B-chromosomes. None of the bulbs free of B's show it. Five bulbs, mosaic for B-content, were identified. Electrophoretic analysis shows that these bulbs are characterised by mosaicism for E-1 isozyme activity. An analysis of individual roots by both electrophoretic and cytological methods shows that tissue mosaicism for B-content correlates with tissue mosaicism for E-1 isozyme activity. The electrophoretic analysis of different roots from bulbs heterozygous for the Est-1 locus indicates that the structural gene for E-1 is not located on the B-chromosome itself. Rather there is a derepressor effect of Bs on E-1 isozyme activity. Since ADH and GOT patterns are unaffected by the presence of B-chromosomes it is clear that they do not exhibit a generalised derepressor effect.     

Molecular cytogenetic characterisation of the terminal heterochromatic segment of the B-chromosome of rye (Secale cereale)

The terminal heterochromatic segments of the long arms of 20 rye B-chromosomes were isolated by means of laser microdissection technology. Also the remaining portions of the long arms, along with the short arms of the same chromosomes were isolated. Each sample was used for degenerate oligonucleotide primer-polymerase chain reaction (DOP-PCR) amplification reactions. The resulting products were used as probes for chromosome in situ hybridisation experiments, and in Southern hybridisation to digests of 0B and +B DNA. Competition hybridisation of these probes with 0B DNA allowed the detection of B-specific sequences. The terminal heterochromatin of the rye B-chromosome contains both B-specific sequences and sequences also present on the A-chromosomes of rye. The B-specific D1100 family is the major repeat species located in the terminal heterochromatin. Primers designed to the cloned sequence (E1100) were used to search for related low copy sequences in 0B DNA. The sequences of the PCR products revealed no similarities to that of the clone E1100 except for the primer sequences. The possible origin of this sequence is discussed in the context of models for the evolution of the rye B-chromosome. EMBL and Genbank accession numbers: Z54196 (E1199): Z54278 (B1) Edited by: R. Appels