Variation of the chromosome phenotype in zea,solanum and salvia

Summary InSolanum lycopersicum pachytene chromosomes the gradient in chromomere size, originating on both sides of the kinetochore, reveals the following characteristics: 1. a relatively abrupt decrease in size of the large chromomeres, 2. the gradient is related to arm length in 9 of the 12 chromosomes, 3. the gradient is particularly irregular in the short arm of the nucleolar chromosome and in the long arm is not conspicuous, 4. chromosome 6 shows an abrupt interruption in the gradient close to the kinetochore. Salvia viridis andZea mays chromosomes represent intermediate conditions between species with well defined and species without gradients. InSalvia the intermediate condition is manifested by the presence of a very large chromomere on each side of the kinetochore followed by very small chromomeres. In two chromosomes the intermediate condition is particularly apparent. In these chromosomes two chromomeres of intermediate size are present in the proximal region of the long arm. The nucleolar organizing arm has also an irregular pattern in this species.Maize has a less distinct gradient than tomato in all its chromosomes. Chromosomes 3, 4, 5 and 8 are those where the gradient is the least sharp. The nucleolar organizing arm of chromosome 6 has also an irregular pattern.In a translocation between chromosomes 5 and 6 of maize, a segment composed of very small chromomeres from the distal region of 5 which was moved to the right of the kinetochore of chromosome 6, did not change appreciably its phenotype after ten years of cultivation. During the period of cultivation a selection was made for plants where the original phenotype was preserved so that this result cannot be considered as demonstrating an absence of change in chromomere phenotype with changed position.InDrosophila andChironomus salivary gland chromosomes where chromomeres are large, and no selection has been carried out with such a purpose, the pattern and nucleic acid content of the bands is known to change when rearrangements occur within the chromosome.Supported by a grant from the Swedish Natural Science Research Council toA. Lima-De-Faria. This work was partly carried out at the Department of Botany, University of Illinois, U.S.A. during a visit to this department byA. Lima-De-Faria.P. Sarvella's collaboration in this work was done during her stay at the University of Lund.     

A new low chromosome number forOrnithogalum tenuifolium (Hyacinthaceae)

A new chromosome number (2n=4) forOrnithogalum tenuifolium Delaroche is reported. The new chromosome race is postulated to have originated by a Robertsonian translocation from a Southern African chromosome race with six chromosomes, and represents thus the final step in a series of decreasing basic number of the species.     

XY<Subscript>1</Subscript>Y<Subscript>2</Subscript> chromosome system in <Emphasis Type="Italic">Salinomys delicatus</Emphasis> (Rodentia,Cricetidae)

Salinomys delicatus is considered a rare species due to its restricted and patchy distribution, poor records and low abundances. It is also the phyllotine with the lowest known diploid chromosome number (2n = 18), however its sex chromosome system has never been described. Here, we studied the chromosomes of six females and three males with bands G, C, DAPI/CMA₃ and meiosis. In males, the chromosome number was 2n = 19, with one large metacentric X-chromosome and two medium-sized acrocentrics absent in females. The karyotype of females was the same as previously described (2n = 18, FN = 32), with X-chromosomes being metacentric and the largest elements of the complement. In males, the two acrocentrics and the large metacentric form a trivalent in meiotic prophase. This indicates that S. delicatus has XY₁Y₂ sex chromosomes, which is confirmed by G and DAPI bands. Constitutive heterochromatin (CH) is restricted to small pericentromeric blocks in all chromosomes. The X-chromosome shows the largest block of centromeric CH, which could favor the establishment of this X-autosome translocation. This sex chromosome system is rare in mammals and, compared with other phyllotine rodents, S. delicatus seems to have undergone a major chromosome restructuring during its karyotypic evolution.     

A comparative chromosome study in the incipient species of the Drosophila paulistorum complex

The gene arrangements in the chromosomes of the races or incipient species of the Drosophila paulistorum complex have been compared in the interracial hybrids. The results are correlated with those obtained by Dobzhansky and Pavlovsky (1962), and also with data on the intraracial polymorphisms, to be published elsewhere. A Standard strain was chosen arbitrarily, the Palmira stock of the Transitional race, and other races and strains described in terms of comparison with the Standard. The minimal number of inverted sections differentiating the Andean race from the Standard is 1, Centroamerican 5, Orinocan 3, Amazonian 6. Little chromosome pairing takes place in the hybrids between the Standard and the Guianan strains. These strains may well be regarded as belonging to a full-fledged species distinct from D. paulistorum complex. The results of the present study furnish little support to the Mayr-Carson hypothesis, according to which diverging incipient species are expected to share few or no intrapopulational polymorphisms.The work reported in this article has been carried under Contract No. AT (30-1)-3096-10, U.S. Atomic Energy Commission.     

Cytomorphological studies in the familySolanaceae from West Pakistan

A project on the chromosome survey of the flora of West Pakistan is in progress and chromosome counts of a large number of species from this region have been reported earlier (Baquar et al. 1965, 1966, 1967). The present paper is a part of this project. Morphological and cytological behaviour of 29 species distributed over 12 genera of the familySolanaceae have been investigated for the first time from West Pakistan. The present investigation shows that the cytological behaviour of the plants of this region is almost similar to those of the other parts of the world. Besides the confirmation of the earlier findings, this report includes four new records namely:solanum albicaule Kotschy n=12;Solanum gracilipes Decne n=12;Withania coagulans Dunal n=24;Datura metel L.n=12.     

Meiosis and pollen mitosis in diploid and triploid Colocasia antiquorum Schott.

The relationship between diploid and triploid forms of Colocasia antiquorum Schott. was assessed through comparative meiotic and pollen mitotic studies. Owing to poor spreading of the chromosomes of both materials, karyological observations on pachytene nuclei were limited to a few chromosomes. Among the two nucleolar chromosomes and a metacentric, telochromomere-bearing chromosome of the diploid, the latter and one of the nucleolar chromosomes characterized by a heteropycnotic short arm were identified in both bivalent and trivalent associations in the triploid. The homologues in these cases were homomorphic and intimately paired. Two types of heteromorphic bivalents exhibiting partial pairing of homomorphic segments were also recorded in the triploid. Among the 14 bivalents of the diploid at diakinesis, two were nucleolus-associated. In the triploid, chromosomal associations at diakinesis included trivalents (2 to 9), bivalents and univalents, and the chiasma frequency per paired chromosome was lower than in the diploids. In 21.6 percent of the PMCs at this stage intragenomic pairing of one or two chromosomes was observed. Post-diakinesis stages in the diploid were regular while in the triploid they were marked by various irregularities in a majority of the cells. However, fertility (stainability), size and divisional frequency of pollen in both materials were remarkably similar. Chromosome numbers in pollen nuclei in the triploid ranged from 8 to 25. Based on these data an autopolyploid origin for the triploid Colocasia and a lower base number than the gametic chromosome number for this genus are advanced.     

Trends in chromosome evolution in the genus Hypostomus Lacépède, 1803 (Osteichthyes, Loricariidae): a new perspective about the correlation between diploid number and chromosomes types

Phylogenetic relationships and identification of species of the genus Hypostomus is still unclear. Considering this, cytogenetics may prove itself as an important tool in understanding the systematic of this genus. Reviews in Hypostomus indicate that the diploid number ranges from 54 to 84 chromosomes, and the increase in diploid number has been associated to higher percentages of subtelocentric and acrocentric chromosomes. Although there is a high number of species in the genus, there are relatively few papers concerning Hypostomus cytogenetics, and most of the data is published as grey literature. With the aim to understand the chromosomal evolution in the genus (correlation between diploid number x chromosomes types), H. ancistroides and H. topavae from the Piquiri River, Upper Paraná River basin, were cytogenetically analyzed, and the diploid number observed was 68 and 80 chromosomes, respectively. Additional data on the diploid number and chromosome formulae was compiled from papers (27 analyses) and abstracts from grey literature (77 analyses). Our analysis shows no correlation between chromosome numbers and percentages of subtelocentric and acrocentric chromosomes for most of the species, since there is considerable variation between these percentages even between species with the same diploid number, indicating that the proportion of chromosome types is not always associated to diploid numbers.     

Chromosome number and ploidy-level in a Dutch population ofCrenobia alpina Dana (Planaria)

A Dutch population ofCrenobia alpina was found to have a chromosome number of 2n=42. One pair of large chromosomes is acrocentric and probably shows a secondary constriction; one small pair is acrocentric as well. All other chromosomes are metacentric or sub-metacentric; it has not been possible to discriminate with certainty between them. According to the hypothesis ofDahm (1958) populations with, 2n=42 are autohexaploid, the basic genome consisting of seven chromosomes. On basis of the karyotype it was concluded that the Dutch population described here, is not autohexaploid but functionally diploid, perhaps allohexaploid.     

Relative DNA content of somatic nuclei and chromosomal studies in three genera,Tilapia, Sarotherodon,andOreochromis of the tribe Tilapiini (Pisces,Cichlidae)

Seven Tilapiine species from three generaTilapia, Sarotherodon, andOreochromis were cytogenetically studied for chromosome number, chromosome morphology, and DNA content. The chromosome number 2n=44 was the same in all seven species. Arm number (NF) differences indicate the possible role of pericentric invasions in the karyotypic evolution of these species. C-banding of metaphase chromosomes shows that heterochromatin is localised around the centromere in all species ofOreochromis and Sarotherodon butT. zillii has more heterochromatin with six chromosomes having completely C-positive short arms. DNA values vary between 0.84 pq forO. macrochir and 1.21 pq forO. aureus. No heteromorphic sex chromosome pair could be found in any species. These findings suggest that karyotypic evolution has occurred but does not appear to be associated with speciation in this group.     

Ultrastructure,meiotic behavior,and evolution of sex chromosomes of the genus Ellobius

The whole-mount SC preparations from males of three species of the genus Ellobius (Ellobius fuscocapillus, Ellobius lutescens), and Ellobius tancrei were studied by electron microscopy. In the males of Ellobius fuscocapillus, behavioral peculiarities of the sex bivalent (viz. the normal male heterozygosity) are characterized by early complete desynapsis of sex chromosomes (X, Y), occurring at late pachytene-early diplotene. The karyotype of species Ellobius lutescens is unique for mammals. In both sexes it is characterized by an odd number of chromosomes (2n=17). At prophase I the unpaired chromosome 9 is not involved in synapsis with other chromosomes and forms a sex body at the end of pachytene.The complete Robertsonian fan has been described for superspecies Ellobius tancrei. As shown on the basis of G-band patterns the male and female sex chromosomes are cytologically indistinguishable.Analysis of whole-mount SC preparations revealed the formation of a closed sex SC bivalent and showed some morphological differences in the axes of sex chromosomes at meiotic prophase I. A number of assumptions are made about the relationship between the behavior of sex chromosomes, their evolution and the sex determination system in the studied species of genus Ellobius.

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On the cytotaxonomy of phasmids (Phasmatodea)

Summary A wide diversity in chromosome complement is found in two species of phasmids of the primitive group Prisopini—Prisopus ariadne Hebard and Prisopus berosus Westwood. P. ariadne has a diploid male complement of 28, comprising 13 pairs of relatively large mediokinetic autosomes and Neo XY sex chromosomes. P. berosus, 2n =49, has relatively small autosomes most of which are mediokinetic, and retains the XO—XX sex mechanism. Chromosomal polymorphism in this species is suggested by the presence of an unequal pair of autosomes and a structural differentiation in the X in one of two males studied.The relative amount of DNA per nucleus in male germ cells (Peulgen cytophotometry) shows a significant difference in total chromosomal content between the complements of the two species.These data are discussed with reference to the cytotaxonomy of phasmids.Supported in part by research grant G-4370 from the National Institutes of Health, Public Health Service.     

Reversion of XO to XY sex chromosome mechanism in a phasmid

Summary The sex chromosomes of the male phasmid Isagoras schraderi Rehn comprise an X and a Y, — each with a submedian kinetochore, and one euchromatic and one heterochromatic arm. At meiosis X and Y form an unequal sex bivalent in which the euchromatic arms are terminally associated. Relatively recent reversion from the XO-XX mechanism characteristic of the Phasmidae is indicated by the presence of the euchromatic arm in both X and Y. The diploid number of the male is 34.Unequal autosomal bivalents are found at meiosis in two other species of Isagoras — Isagoras subaquiles Rehn and Isagoras sp. — and in Pseudophasma menius Westwood. The chromosome complements of these species are described.     

A sexual difference in the chromosomes of two species of agamid lizards

Summary The diploid number of chromosomes in Calotes versicolor is 34 in the male and 33 in the female. The numerical difference in the two sexes is based on the condition of the sex chromosome; in the male it is present as a homologous pair, while in the female it remains unpaired. The sex chromosome was identified as one of the micro-chromosomes (the chromosome No. 7) in this species. Sitana ponticeriana possesses the diploid number of 46 in the male and 45 in the female. The sex chromosome identified in this form is also one of the micro-chromosomes (chromosome No. 13), which has no partner in the female, whereas in the male it is in the paired state having a homologous mate.It was established therefore that, in both species studied, the female is heterogametic as regards the sex chromosome.The chromosome complement of Calotes versicolor consists of 12 V-shaped macro-chromosomes and 22 dot-like micro-chromosomes, while in Sitana ponticeriana there are 24 rod-shaped macro-chromosomes and 22 dot-like micro-chromosomes. The difference in the karyotypes of these two species can be accounted for on the basis of the formation of V-shaped multiple chromosomes by means of the fusion of two rods at the point of fibre attachment.The karyological relationships in the Family Agamidae were discussed. The chromosome number previously reported for Uromastix hardwicki was found to be erroneous; the diploid number in this species is 34.Contribution No. 214 from the Zoological Institute, Faculty of Science, Hokkaido University, Sapporo, Japan.     

Geographical variation of chromosomal structure in Drosophila gasici

Summary Drosophila gasici Brncic 1957, is a neotropical species found in several parts of the Andes Mountain System. By means of the analysis of their external characteristics, chromosomes and hybridization test they have been included in the mesophragmatica group of species of the sub-genus Drosophila.The present paper describes the mitotic and polytene chromosomes of D. gasici from samples of natural populations collected at Bogotá (Colombia), Cochabamba (Bolivia), Arica (Chile) and San Luis (Argentina). The comparative study of all these populations has disclosed that the species has split in well defined geographic races. The Colombian and Chilean flies differ from those living in Bolivia and Argentina by three independent inversions in chromosome I (the sexual pair). The only polymorphic populations seem to be the Chilean ones which exhibit two inversions in the second chromosome, besides the Standard gene arrangement. All the other populations are homozygous for all their chromosomal sequences. Studies on reproductive isolation have demonstrated that there is some sexual discrimination between the Colombian and Chilean flies in respect to the Bolivian and Argentinean ones.The populational structure of D. gasici is in contrast to that observed in the other six species belonging to the mesophragmatica group in which there are no good evidences of geographical variations at the chromosomal level.This article is dedicated to Professor Hans Bauer on the occasion of his 60th birthday.     

Die kinetische Organisation der Lepidopteren-Chromosomen

In monokinetic chromosomes half of the recombinations from reciprocal translocation are expected to be lethal owing to the formation of bikinetic and akinetic chromosomes. In holokinetic chromosomes all reciprocal recombinations should be viable, because all again are holokinetic. This difference can be used as a tool other than the study of fragment behaviour to decide which type of chromosome is present in an animal species. — Pieris brassicae males X-rayed with 6,000 r units and mated to normal females gave in F₁ only 19.9% lethal zygotes (14.7% of which dying late) as compared to a control mortality of about 7.7%. Among the hatched male caterpillars cytologically tested in the last larval instar 64.9% contained in their spermatocytes 1 to 4 heterozygous translocation rings or chains consisting of from 4 to 14 chromosomes. Translocations of similar frequency and even greater complexity have been observed in preliminary experiments on Philosamia cynthia. — The discrepancy between these results and those on species with monokinetic chromosomes (Drosophila, Phryne etc.) where very high zygotic lethality is observed at comparable Röntgen doses is proof of the holokinetic nature of Pieris and Philosamia chromosomes. Together with earlier results on Bombyx mori by Astaurow and Frolowa and the cytogenetic studies especially by Seiler sufficient proof exists to conclude that all Lepidoptera have holokinetic chromosomes. — A survey of the known groups of organisms with chromosomes of this type leads to the assumption that holokinetic chromosomes must be derived from monokinetic ones. The problems connected with this change in kinetic organisation of chromosomes are discussed.

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Herrn Professor Dr. J. Seiler ist diese Arbeit in herzlicher Dankbarkeit für in mehr als 40 Jahren gewachsene Freundschaft zu seinem achtzigsten Geburtstag gewidmet worden.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Cytogenetic evidence for the specific distinction of an Alaskan marmot,Marmota broweri Hall and Gilmore (Mammalia: Sciuridae)

Summary Cytogenetic studies based upon somatic cells (bone marrow) have disclosed that the marmot hitherto designated Marmota caligata broweri Hall and Gilmore, occurring in the Brooks Range of arctic Alaska, differs from M. c. caligata (Eschscholtz) in number of chromosomes (2n=36 as compared with 2n=42 in M. caligata) and in proportions of chromosomal types. Typical karyograms for the two species are presented. It is concluded that the Brooks Range marmot is specifically distinct from M. caligata, the applicable name being Marmota broweri Hall and Gilmore. Also determined were diploid chromosome numbers for two other Nearctic species of marmots, M. flaviventris (Audubon and Bachman), with 42, and M. olympus (Merriam), with 40. It is suggested that M. broweri survived the last (Wisconsin) glaciations in the amphi-Beringian refugium, and that its closest affinities may be with one of the Eurasian species of Marmota.     

Centromeric repetitive DNA sequences in the genus Brassica

Representatives of two major repetitive DNA sequence families from the diploid Brassica species B. campestris and B. oleracea were isolated, sequenced and localized to chromosomes by in situ hybridization. Both sequences were located near the centromeres of many chromosome pairs in both diploid species, but major sites of the two probes were all on different chromosome pairs. Such chromosome specificity is unusual for plant paracentromeric repetitive DNA. Reduction of stringency of hybridization gave centromeric hybridization sites on more chromosomes, indicating that there are divergent sequences present on other chromosomes. In tetraploid species derived from the diploids, the number of hybridization sites was different from the sum of the diploid ancestors, and some chromosomes had both sequences, indicating relatively rapid homogenization and copy number evolution since the origin of the tetraploid species.     

Chromosomes tell half of the story: the correlation between karyotype rearrangements and genetic diversity in sedges,a group with holocentric chromosomes

Chromosome rearrangements may affect the rate and patterns of gene flow within species, through reduced fitness of structural heterozygotes or by reducing recombination rates in rearranged areas of the genome. While the effects of chromosome rearrangements on gene flow have been studied in a wide range of organisms with monocentric chromosomes, the effects of rearrangements in holocentric chromosomes—chromosomes in which centromeric activity is distributed along the length of the chromosome—have not. We collected chromosome number and molecular genetic data in Carex scoparia, an eastern North American plant species with holocentric chromosomes and highly variable karyotype (2n = 56–70). There are no deep genetic breaks within C. scoparia that would suggest cryptic species differentiation. However, genetic distance between individuals is positively correlated with chromosome number difference and geographic distance. A positive correlation is also found between chromosome number and genetic distance in the western North American C. pachystachya (2n = 74–81). These findings suggest that geographic distance and the number of karyotype rearrangements separating populations affect the rate of gene flow between those populations. This is the first study to quantify the effects of holocentric chromosome rearrangements on the partitioning of intraspecific genetic variance.     

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.     

THE PROBLEM OF PLOIDY IN ECHEVERIA (CRASSULACEAE) I. DIPLOIDY IN E. CILIATA

The largely Mexican genus Echeveria is characterized by an extensive series of dysploid chromosome numbers, with every gametic number from 12 to 34 known in at least one species. Within this nearly three-fold range of numbers, the boundary between diploidy and tetraploidy is not immediately apparent. However, species of Echeveria can be hybridized in an extraordinary number of combinations, both among themselves and with related genera, and study of the morphology of the hybrids and the pairing of their chromosomes provides information that helps to identify the ploidy of the parents. This paper reports observations from study of 80 hybrids between E. ciliata (n = 25) and 73 other species and/or cytotypes. Hybrids between E. ciliata and definite diploids are all nicely intermediate morphologically, whatever the chromosome numbers. In these same hybrids, most chromosomes become involved in pairing at meiosis, and the number of paired elements (bivalents and multivalents) approaches or equals, but never exceeds, the number of chromosomes received from the lower-numbered parent. In most cells, relatively few univalents are present, sometimes none. These observations are considered to indicate that all paired elements include at least one chromosome from each parent and therefore that pairing occurs between chromosomes of different parents only (allosyndesis). Since none of the 25 gametic chromosomes of E. ciliata is able to pair with any other, although they do pair very extensively with chromosomes from many other species having a wide range of numbers, E. ciliata is considered to be diploid in spite of its relatively high chromosome number. On the other hand, hybrids of E. ciliata with definite polyploids resemble the latter much more closely in their morphology, and at meiosis most or all pairing occurs by autosyndesis between chromosomes received from the polyploid parent, while the chromosomes from E. ciliata generally remain unpaired. In these respects most, but not all, species of Echeveria having as many as 34 gametic chromosomes have the same properties as E. ciliata and also are considered to be diploid. The ancestral chromosome number in the genus is not clear, but it is probably near the upper end of the series of dysploid numbers.