Quantitative karyology of some species ofLuzula

The dimensions of metaphase chromosomes and nuclear DNA contents were measured in eight species ofLuzula. The 2 C DNA contents ranged from 8.51 pg inL. purpurea to 0.55 pg inL. pilosa. Total chromosome volume shows a linear relationship with DNA content; however, the total chromosome length of the complement of the different species is approximately constant. Nucleolar volume and the number of chromocentres in the different species also show a relationship with DNA content. Taken together, these data suggest that while chromosome fragmentation could have generated the present-day range of chromosome numbers in the genus, there have also been changes in the total quantity of DNA with the result that species with similar chromosome numbers have different DNA contents. The relationships of DNA content with chromosome volume inLuzula and other genera are compared and the differences discussed.     

In situ hybridization to metaphase chromosomes in six species ofPhaseolus andVigna using ribosomal DNA as the probe

In situ hybridization with a biotin-labeled rice ribosomal DNA (rDNA) probe to the somatic metaphase chromosomes of six species ofPhaseolus andVigna (P. angularis, P. calcaratus, P. coccineus, P. vulgaris, V. sesquipedalis andV. sinensis) was done to determine the sites of rDNA. Hybridization signals were present in the terminal and subterminal chromosome regions of each of the six species. The number of rDNA sites was two inP. angularis andP. calcaratus, four inP. coccineus andP. vulgaris, and six inV. sesquipedalis andV. sinensis.     

Phylogeny of the slow lorises (genusNycticebus): An approach using mitochondrial DNA restriction enzyme analysis

Mitochondrial DNA polymorphisms in 15 specimens of three species of slow lorises-Nycticebus coucang, N. intermedius, andN. pygmaeus-were analyzed in order to study the evolutionary relationships among the species. Eight restriction types were observed in the samples. Phylogenetic trees constructed on the basis of genetic distances showed that the slow lorises sort into two clusters: four types ofN. coucang and three types ofN. intermedius plus one type ofN. pygmaeus. Our results suggest that there are two valid species in the genusNycticebus-N. coucang, andN. pygmaeus-and thatN. intermedius should be included withinN. pygmaeus. Divergence between the two species may have begun 2.7 Ma (million years ago). Evolution of gross morphology, chromosomes, and mitochondrial DNA in the slow lorises appears to be concordant.     

Chromosomal evolution in Malagasy lemurs: X. chromosomal banding studies of Propithecus diadema edwardsi and Indri indri and phylogenic relationships between all the species of the Indriidae

The R-banded karyotypes of two Indriidae, Propithecus diadema and Indri indri, are described and compared with each other and with those of the other species of this family, previously reported, Avahi laniger and Propithecus verreauxi. These comparisons show that 30 chromosomal rearrangements, including 21 Robertsonian translocations and eight pericentric inversions, differentiate these karyotypes. A phylogenic diagram is proposed, showing the early separation of Avahi and the relatively late divergence of the three other species. A populational evolution has occurred between the three other species, but Indri is clearly separated from the two other species by at least five complex rearrangements, although it shares four Robertsonian translocations with P. verreauxi but not P. diadema.     

Studies on the chromosomes of genusNycticebus

The karyotypes of three species (N. coucang, N. intermedius, andN. pygmaeus) of genusNycticebus, collected from the southern Yunnan of China, have been studied. All individuals from three species possess 2n=50 chromosomes, and all chromosomes in their complement are biarm chromosomes. The karyotype of slow loris (N. coucang) is characterized by having a secondary constriction and Ag-NORs in the short arms of pair No. 1. The G-banding patterns of three species are very similar. Three species are found to have multiple Ag-NORs. InN. coucang, NORs were observed on five pairs (Nos. 1, 6, 9, 15, and 23) and inN. intermedius andN. pygmaeus, NORs were found on four pairs (Nos. 6, 9, 15, and 20). This finding indicates that slow lorises, as primitive primates, also have multiple NOR-bearing chromosomes. Finally, the classification of genusNycticebus by karyotype analysis is discussed, and our results suggest that there are at least two valid species, namely:N. coucang andN. pygmaeus.     

Chromosome cytology and karyotype change inGalaxia (Iridaceae)

Basic chromosome number inGalaxia is believed to be x = 9, and this number, or multiples, occurs in all species of subgenusGalaxia. In subgenusEurystigma, G. barnardii has n = 8,G. versicolor n = 8 and 7,G. citrina n = 8, 7 and 17 whileG. variabilis has n = 7 exclusively. Karyotypes in forms ofG. versicolor with n = 7 and inG. variabilis are quite different and clearly originated independently. Karyotypic features provide evidence for the hypothesis that changes in chromosome number were accomplished through chromosome fusion either by classical Robertsonian translocation, or unequal reciprocal translocation.     

Synthesis of an attached autosome,C(3)RM,inDrosophila pseudoobscura

Drosophila pseudoobscura has three acrocentric autosomes. In the experiments reported, homologous arms of the third chromosome were attached to the same centromere. This is a reversed metacentric compound third chromosome, denoted by C(3)RM. This compound chromosome is relatively fertile in within-strain crosses (ca. 50% egg hatch) but sterile when outcrossed to a normal karyotype. When constructing translocations for this experiment, the behavior of the Y-autosome translocations suggested that this species can tolerate more Y chromosome deficiency while retaining fertility than canDrosophila melanogaster. Finally, there were no Robertsonian exchanges observed among the 96 autosome-autosome translocations analyzed cytologically.     

A molecular genetic approach to the identification of isochromosomes of chromosome 21

Summary The largest class of de novo chromosomal rearrangements in Down syndrome are rea(21q21q). Classically, these rearrangements have been termed Robertsonian translocations, implying an attachment of two different chromosome 21 homologues. Additionally, a Robertsonian translocation between two chromosomes 21 cannot be distinguished from an isochromosome composed of genetically identical arms by cytogenetic analyses. Therefore, we have used molecular techniques to differentiate between true Robertsonian translocations and isochromosomes. Samples were obtained from 12 probands, ascertained for de novo rearrangements between homologous chromosomes 21 [11 rea(21q21q) and 1 rea (21;21)(q22;q22)], their parents (n = 24) and available siblings (n = 7). The parental origins of the de novo rearrangements were assigned using molecular and cytogenetic analyses. Although not statistically significant, there was a two-fold increase in the number of paternally derived de novo rearrangements (n = 8) as compared with maternally derived rearrangements (n = 4). To distinguish between rob(21q21q) and i(21q), we used restriction fragment length polymorphisms (RFLPs) spanning the length of chromosome 21. Using all informative and partially informative RFLPs, we used the method of maximum likelihood to assign the most likely rearrangement definition (i or rob) and parental origin in each family. The maximum likelihood estimates indicated that all rearrangements tested (n = 8) were isochromosomes. C-banding revealed two centromeres in three cases indicating that a U-type exchange occurred between sister chromatids in these rearrangements. Our results suggest that the majority of de novo rea(21q21q) are isochromosomes derived from a single parental chromosome 21.     

Chromosomal polymorphism in the house mouse (Mus domesticus) of Greece and Yugoslavia

A total of 88 wild mice from the Dalmatian coast of Yugoslavia (35 animals), and Peloponnesus (30 animals) and Thebes (23 animals) on mainland Greece were karyotyped. In all but five animals Robertsonian translocations were found. Mice from the Dalmatian region were homozygous for translocations Rb(5.15), Rb(6.12), Rb(8.17), Rb(9.13), and Rb(10.14); they were homo-or heterozygous for the translocation Rb(1.11). Some of them lacked the Rb(1.11) translocation altogether so that the diploid numbers in the Yugoslavian mice were 2n=28, 29, 30, or 40. The mice from the vicinity of Olympia in northwestern Peloponnesus were homozygous for eight Robertsonian translocations: Rb(1.3), Rb(2.5), Rb(4.6), Rb(8.12), Rb(9.16), Rb(10.14), Rb(11.17), and Rb(13.15). Their diploid chromosome number was therefore 2n=24. Mice from the vicinity of Patras in northwest Peloponnesus carried all except the first three of these eight translocations; their chromosome number was 2n=30. Finally, the mice from Thebes were homozygous for translocations Rb(2.15), Rb(4.14), Rb(5.12), and Rb(10.13). They were homo- or heterozygous for Rb(6.9), Rb(8.17), and Rb(1.11); some mice lacked the Tb(1.11) translocation altogether. The translocations Rb(6.9)40Tu and Rb(10.13)42Tu represent new arm combinations not found previously in any wild mouse population. the remaining translocations have previously been found in different Mediterranean countries, in Scotland and in southern Germany. The findings suggest that each translocation arose only once and that different translocations have come together in different populations to generate a unique karyotype characterizing this population.     

Alloparental care in the marine sculpinAlcichthys alcicornis (Pisces: Cottidae): Copulating in conjunction with paternal care

The elkhorn sculpinAlcichthys alcicornis spawns and subsequently copulates, and the eggs are then cared for by the male. DNA fingerprinting was used to determine the paternity of males for the clutches guarded by them. When a female was mated with 4 males in succession in aquaria, males did not fertilize the eggs spawned just before copulation unless the female was unimpregnated but fathered the eggs spawned by the female later. In the field, near the end of the breeding season, males were genetically unrelated to the clutches in their territories. We concluded that males guard non-kin eggs for the opportunity to copulate and to fertilize the future clutches of their mates.     

Karyology and nuclear DNA quantification of four species ofChaetomorpha (Cladophorales,Chlorophyta) from the western Atlantic

Chromosome numbers are given for four species ofChaetomorpha from the warm temperate and tropical western Atlantic. The basic chromosome number is six, with three median and three submedian chromosomes.Chaetomorpha species represent a polyploid series, with numbers of 12, 18 and 24 found in the present study. Microspectrophotometry data for each species were quantified by reference to standards with known DNA contents. Results indicate similar 2X =1C=12 genome sizes forC. aerea (0.20 pg) andC. brachygona (0.26 pg), and forC. antennina (0.53 pg) andC. melagonium (0.58 pg). These findings are compared with karyological features ofCladophora species to characterize the karyology of the cladophoralean genome.     

Karyological and taxonomical notes on three species of the genus<Emphasis Type="Italic">Epipactis (Neottioideae,Orchidaceae)</Emphasis> in the central-western Iberian Peninsula

Studies on the karyotypes and chromosome numbers of species ofEpipactis from the central-western Iberian Peninsula show that the species harbour enormous chromosome variability, have very asymmetric karyotypes and possess extraordinary diversity of aneuploidy. This paper provides the first report of a chromosome number forE. fageticola (2n=36, 40 + 0–2 B), as well as the first counts for Portuguese populations ofE. helleborine (2n=18, 32, 38) and first counts for Iberian populations ofE. tremolsii (n=20, 30, 2n=16, 24, 32, 34, 36, 38 + 1B, 40 + 1B, 52, 60). Among populations ofE. tremolsii there is a significant differentiation in ecology and somatic chromosome number, suggesting that there may be two different taxa in the region studied. Chromosomes are large to small, ranging in length from 10.8 μm to 1.8 μm. Karyotype asymmetry is of type 3C inE. fageticola andE. tremolsii and 2C inE. helleborine andE. tremolsii.     

Chromosomal and molecular evolution in Asiatic wild asses

Chromosomal studies of Tibetan wild ass,Equus kiang holdereri are reported for the first time. A Robertsonian polymorphism resulting in diploid numbers of 2n=51 and 2n=52 was identified. This polymorphism involves the same elements that participate in the polymorphic Robertsonian rearrangement producing diploid numbers of 54–56 inE. hemionus kulan andE. hemionus onager. Comparison of mitochondrial DNA restriction fragment patterns among three unrelated kiang individuals and between kiangs and a Transcaspian kulan,E. hemionus kulan, indicates an approximately 1% nucleotide sequence divergence of mitochondrial DNAs between the two taxa. The chromosomal divergence betweenE. hemionus andE. kiang probably originated less than 500,000 years ago. Studies of additional Asiatic wild ass taxa are indicated in order to gain further insights into the speciation and systematics of this threatened group of mammals.     

Chromosome numbers of miscellaneous Malagasy Acanthaceae

Meiotic chromosome numbers are reported for 12 species in eight genera of Acanthaceae from Madagascar. Chromosome numbers of 11 species are reported for the first time. Counts inMendoncia (n=19) andNeuracanthus (n=20) are the first for these genera. A new chromosome number (n=30) is reported inJusticia. Systematic implications of the chromosome counts are addressed and basic chromosome numbers for these eight genera of Malagasy Acanthaceae are discussed.     

Chromosomal evolution inEpilobium sect.Epilobium (Onagraceae)

WithinEpilobium sect.Epilobium, a cytological analysis of 121 experimental hybrids, involving 40 species, indicates the presence of a widespread BB chromosome arrangement in Eurasia, Africa, and Australasia, as well as in North and South America less commonly. The AA chromosome arrangement, which differs from BB by one reciprocal translocation, occurs in North America, South America, and in at least three European species. The CC arrangement, which differs from AA by two reciprocal translocations, characterizes theAlpinae, a circumboreal group. Distinctive or only partly worked out chromosome arrangements occur in the EuropeanE. duriaei andE. nutans and in the North AmericanE. luteum, E. obcordatum, E. oregonense, andE. rigidum. With earlier results, the chromosome arrangements of some 65 of the estimated 185 species of the section have been established fully or partly.     

Chromosomal variations in the callus tissues ofAllium tuberosum andA. cepa

Summary Chromosome studies ofAllium tuberosum andA. cepa were made from one month to eighteen months old calluses. Different types of chromosomal variations like aneuploid number ranging from 28 to 31, tripolarity, lagging, micronuclei, haploid number etc. were noted inA. tuberosum, whereas inA. cepa the cells showed high chromosome numbers such as 32, 64 or more. The normal chromosome number (2n=16) occurred rarely. The selective pressure of the culture media may have led to the manifestation of the genetic control of differential response to chromosome behaviour and growth in the two species of the same genus.     

Genome size in gymnosperms

The DNA 2C and per chromosome values of 57 species belonging to 22 genera of gymnosperms have been analysed. The overall range is 12-fold with a modal value of about 30.0 pg.Cycadales exhibit a 2-fold difference. AmongConiferales with a 4-fold variation, thePinaceae have higher mean DNA contents as well as a greater range and diversity than other families. Remarkable interspecific differences are found inCycas, Picea, Larix, Pinus, Callitris, Cupressus, andChamaecyparis. Despite this, there is a constancy of basikaryotypes within these genera.Gnetum shows a distinctly low DNA value.     

Comparative cytogenetics of six Indo‐Pacific moray eels (Anguilliformes: Muraenidae) by chromosomal banding and fluorescence in situ hybridization

A comparative cytogenetic analysis, using both conventional staining techniques and fluorescence in situ hybridization, of six Indo‐Pacific moray eels from three different genera (Gymnothorax fimbriatus, Gymnothorax flavimarginatus, Gymnothorax javanicus, Gymnothorax undulatus, Echidna nebulosa and Gymnomuraena zebra), was carried out to investigate the chromosomal differentiation in the family Muraenidae. Four species displayed a diploid chromosome number 2n = 42, which is common among the Muraenidae. Two other species, G. javanicus and G. flavimarginatus, were characterized by different chromosome numbers (2n = 40 and 2n = 36). For most species, a large amount of constitutive heterochromatin was detected in the chromosomes, with species‐specific C‐banding patterns that enabled pairing of the homologous chromosomes. In all species, the major ribosomal genes were localized in the guanine‐cytosine‐rich region of one chromosome pair, but in different chromosomal locations. The (TTAGGG)_n telomeric sequences were mapped onto chromosomal ends in all muraenid species studied. The comparison of the results derived from this study with those available in the literature confirms a substantial conservation of the diploid chromosome number in the Muraenidae and supports the hypothesis that rearrangements have occurred that have diversified their karyotypes. Furthermore, the finding of two species with different diploid chromosome numbers suggests that additional chromosomal rearrangements, such as Robertsonian fusions, have occurred in the karyotype evolution of the Muraenidae.     

Robertsonian translocations in wheat arise by centric misdivision of univalents at anaphase I and rejoining of broken centromeres during interkinesis of meiosis II

The mechanism of origin of Robertsonian translocations was investigated in plants monosomic for chromosome 1A of wheat and 1H(t) of Elymus trachycaulus by GISH. Chromosomes 1A and 1H(t) stayed univalent in all metaphase I cells analyzed, suggesting that Robertsonian translocations do not originate from meiotic recombination in centromeric regions with shared DNA sequence homology. At ana-/telophase I, the 1H(t) and 1A univalents underwent either chromosome or chromatid segregation and misdivided in 6-7% of the pollen mother cells. None of the ana-/telophases I analyzed had Robertsonian translocations, which were only observed in 2% of the "half tetrads" at ana-/telophase II. The frequency of Robertsonian translocations observed at ana-/telophase II corresponds well with the number of Robertsonian translocations (1-4%) detected in progenies derived from plants monosomic for group-1 chromosomes of wheat (1A, 1B, and 1D) and 1H(t) of E. trachycaulus. Our data suggest that Robertsonian translocations arise from centric misdivision of univalents at ana-/telophase I, followed by segregation of the derived telocentric chromosomes to the same nucleus, and fusion of the broken ends during the ensuing interkinesis.     

Evidence for structural heterogeneity from molecular cytogenetic analysis of dicentric Robertsonian translocations.

Most Robertsonian translocations are dicentric, suggesting that the location of chromosomal breaks leading to their formation occur in the acrocentric short arm. Previous cytogenetic and molecular cytogenetic studies have shown that few Robertsonian translocations retain ribosomal genes or beta-satellite DNA. Breakpoints in satellite III DNA, specifically between two chromosome 14-specific subfamilies, pTRS-47 and pTRS-63, have been indicated for most of the dicentric 14q21q and 13q14q translocations that have been studied. We have analyzed the structure of 36 dicentric translocations, using several repetitive DNA probes that localize to the acrocentric short arm. The majority of the translocations retained satellite III DNA, while others proved variable in structure. Of 10 14q21q translocations analyzed, satellite III DNA was undetected in 1; 6 retained one satellite III DNA subfamily, pTRS-47; and 3 appeared to contain two 14-specific satellite III DNA sub-families, pTRS-47 and pTRS-63. In 10/11 translocations involving chromosome 15, the presence of satellite III DNA was observed. Our results show that various regions of the acrocentric short arm, and, particularly, satellite III DNA sequences, are involved in the formation of Robertsonian translocations.