High Chromosome Numbers Research Articles

Systematic implicationsofflavonoid patterns in Haplopappus segregates

Complex flavonoid patterns are correlated with primitive woody taxa and high base chromosome numbers among Haplopappus segregates. Variability among flavonoid complements supports the polyphyletic interpretation of the genus.

A Double Spore Wall in Macroglossum

Since the original description of Macroglossum alidae by Copeland (1909a, p. 343; 1909b, p. 9), little has been learned about this strange and primitive member of the Marattiales. Campbell (1911, 1914a, 1914b) has dealt with the anatomical aspects of the gametophytes and sporophytes but, surprisingly, he gives no description of the spores. In Erdtman (1957, p. 79), the proximal and distal faces of M. alidae are illustrated both in surface view and in optical section; the is globose but distally flattened, with an irregular and sparsely tuberculate exine. Kremp & Kawasaki (1972, p. 4) described the from seven specimens as rounded-triangular (32.4 x 28.7 gLm), trilete, and scabrate. The observation of of M. alidae (Molesworth-Allen 3197, US) under the SEM shows a regularly and densely tuberculate-subbacillate perispore (Fig. 1), the shape and dimensions of which are in agreement with the foregoing authors. An unusual case of double-walled is shown in Fig. 2, a preparation from the same specimen. In it, the outer exine layer is cracked to reveal a smaller but morphologically perfect inside, one per parent spore. This phenomenon is hitherto unreported in the fern literature but may not be rare, for we have observed a parent spore ofBotrychium sp. containing four daughter spores, and it is quite possible that such occur in other pteridophytes. The biosystematic implications of angiospore production are, as yet, unknown. Research is needed to elucidate various questions that come to mind, including: (a) What, if any, percentage of angiospores is viable? (b) What is their genotype and resulting phenotype? (c) What is the ploidy level of angiospores in relation to parent spores? (d) Do angiospores represent a reduction mechanism for polyploidal pteridophytes? (e) Within a sporangium, what percentage of parent spores contain angiospores? (f) What effect would this ratio have on the population structures of the resulting gametophytic and sporophytic generations? (g) Does the smaller size the angiospores have any effect on the range and pattern of their dispersibility? (h) Is angiospory a primitive trait only to be found in eusporangiate pteridophytes? Spore size and shape, of themselves, are not indicative of viability. Recent literature abounds with examples of the germination of supposedly non-viable abortive in hybrids and of larger than normal diplospores formed through ameiotic apogamy. At present, questions (b) and (d) are unanswerable due to the lack of appropriate materials. The fact that the cytology of Macroglossum has never been investigated prevents speculation on whether angiospores represent any change in ploidy level, be it reduction or augmentation. The Marattiales have high chromosome numbers as do the Ophioglossales, the only other instance in which we have as yet observed angiospory. Until a large enough quantity of both parent spores and angiospores are cultured, questions (e) and (f) also remain unanswerable.

Chromosomal variations in the callus tissues ofAllium tuberosum andA. cepa

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.

The unusual karyotype of the lesser kudu, <i>Tragelaphus imberbi</i><i>s</i>

The chromosome set of the lesser kudu, Tragelaphus imberbis, consists of 38 elements in both sexes. In contrast to most other members of the bovid subfamily Tragelaphinae, both the X and the Y chromosomes are compound, having fused with identical autosomes from ancestors presumed to have higher chromosome numbers. From a comparison of the unusual sex chromosomal rearrangements that have occurred in this family, a hypothetical lineage has been derived. This family tree and the details of various banding studies in the lesser kudu are described.

Genetic system relationships inTrifolium

Examination of species of Trifolium in the Kentucky collection revealed that annual species generally have simple tap roots, low chromosome numbers (2n = 10−32), are usually self-pollinating and many were introduced from a Mediterranean type climate. Perennial species generally are tap-rooted, stoloniferous, or rhizomatous, possess higher chromosome numbers than annuals (2n = 12− 130), are mostly cross-pollinating and do not have specific climate-habitat relationships. Species introduced from Eurasia are more numerous and more diverse in base chromosome number (n = 5−8) than from other origins. Only species with diploid chromosome numbers of 16 or higher are stoloniferous or rhizomatous. Rhizomatous species, mostly cross-pollinated, were introduced from Eurasia, North and South America, but not from Africa, and not often from Mediterranean climates. Self- and cross-pollinated species occur in all origins. Different flower colors and leafmarks are not associated with origins, climates, and other morphological and physiological characteristics.

Transfer of resistance to race 2 of Plasmodiophora brassicae from Brassica napus to cabbage (B. oleracea ssp. capitata). III. First backcross and F2 progenies from interspecific hybrids between B. napus and B. oleracea ssp. capitata

The first backcross and F2 progenies from triploid F1 and tetraploid F1 hybrids between B. napus and 2x and 4x B. oleracea ssp. capitata (cabbage) were studied for their general morphology, resistance to race 2 of the clubroot pathogen, chromosome number and meiotic chromosome behavior. No linkage was apparent between resistance and the major morphological characters. Unreduced gametes played a large part in the successful formation of seed of the B1 and F2 progeny. B1 plants with low chromosome numbers were selected for use in recurrent backcrosses. The potential use of anther culture to extract gametic progenies from resistant B1 and F2 plants with higher chromosome numbers was suggested. The presence of homoeologous pairing observed in all the plants is considered advantageous for selecting suitable progeny in later generations.

Occurrence of Various Cytotypes ofOphioglossum ReticulatumL. in a Population from N. E. India

SUMMARYA population of Ophioglossum reticulatum L. growing in an area of c. 1500 sq. metres in Darbhanga (N. Bihar), India exhibited marked morphological differences. Sampling of the morphological variants led to the delimitation of five groups in the population. Of this, three were confined to moist shady place and the other two to open dry condition. Meiotic investigations carried out in these groups revealed differences in chromosome numbers which indicated different ploidy levels. The lowest number of 112–114 bivalents and 8–12 univalents has been encountered in one group and constitutes the first report of a diploid count from this country. Other numbers counted were 194–200 bivalents, 375–380 bivalents and 632–640 bivalents with 6–12 univalents in each. The univalents may represent fragments. Polyploidy has been suggested to be the dominant genetic theme in homosporous pteriodophytes. Storage and release of genetic variability through polyploidy may have provided evolutionary adaptability to this genus, known for its ancient history and high number of chromosomes.

Chromosome Studies inCryptocoryne(Araceae)

SUMMARYTwo species of Cryptocoryne, namely C. ciliata and C. spiralis have been found to have 2n=22 and 90 chromosomes, respectively. The latter species with the highest number of chromosomes in this genus has possibly been derived through allopolyploidy, as evidenced by characteristic meiotic irregularities.

Primary Basic Chromosome Numbers in Ferns: Facts or Fantasies?

Several workers have attempted karyotypic analysis of ferns and con- cluded that the high chromosome numbers that characterize extant fern genera reflect high polyploidy. An examination of fern karyotypic data suggests that ob- served differences in total length and arm length ratio between chromosomes and chromosome groups are subject to many errors. The possibility of such errors sug- gests that karyotypic analysis in ferns is a dubious practice. We have applied graphic and statistical methods of analysis to karyological data previously published by Ta- tuno and others and conclude that unreasonable inferences have been made from the karyotypic data. These data are consistent with an hypothesis that fern evolution at the generic level occurred from ancestors that had essentially the same high chromosome numbers observed in living ferns. In a series of papers dealing with karyotypic analyses of ferns and fern allies, Tatuno (1963), Tatuno and Yoshida (1966, 1967), Tatuno and

Genetic instability in somatic hybrids of Nicotiana tabacum and Nicotiana knightiana

Somatic hybrids of Nicotiana knightiana (2n=2X=24) and an albino mutant of Nicotiana tabacum (2n=4X=48) were selected after polyethylene glycol induced protoplast fusion. Three lines were selected on the basis of the simultaneous expression of shoot inducibility and green pigmentation, traits originally separated in the parental species. The hybrid nature of the lines was confirmed by their characteristic isoenzyme patterns, the morphology of the regenerated plants, and by the appearance of heterochromatic blocks in the interphase nuclei. Chromosome numbers in the somatic hybrids varied greatly within individual plants. Variegation in leaf and flower colour and segregation for morphological traits in vegetatively multiplied plants are attributed to segregation of chromosomes in the somatic cells, a consequence of the numerical instability. Hybridity, caryotypic changes induced by tissue culture, and high chromosome numbers, are discussed as possible reasons for the observed genetic instability.

Pairing restriction and non-homologous pairing in autoploids of Adiantum capillus-veneris.

The high basic chromosome numbers in homosporous ferns are polyploid in origin, and their haploid chromosome complements may contain two or more homoeologous sets of chromosomes (Klekowski 1973). Therefore, chromosome associations in three generations of an autotetraploid of the Venus-hair fern, Adiantum capillus-veneris, have been analysed to test the possibility of a fully penetrant genecontrolled mechanism in the so-called diploid homosporous ferns which limit chromosome associations to only bivalents. Multivalent formation occurs in the autotetraploids, which, though not unexpected, is against a simple gene control to form only bivalents. In the autotetraploid, there are relatively fewer quadrivalents and more bivalents. In the autotriploid, the frequency of trivalents compares closely with those of quadrivalents in the autotetraploids. The occurrence of large number of bivalents in the autotetraploids have been accommodated partly in the model of John and Henderson (1962) which assumes random association of chromosomes within each homologous set. Further accentuation in the number of bivalents occurs partly owing to proximal chiasmata, and partly due to a pairing restriction upon multivalent formation. Following Timmits and Rees (1971), it has been estimated that at least five of the thirty homologous sets in the autotetraploids and autotriploid of A. capillus-veneris associate themselves exclusively in pairs. Chromosome analysis in the autotriploid has also revealed evidence of non-homologous pairing, which seemingly supports the concept of “homoeologous” genomes comprising the haploid complements of extant diploid species in ferns, and also raises the probability of occasional homoeologous pairing and recombination coupled with the pairing restriction.

Chromosome Numbers and Meiosis in North and Central American Species of Centaurium (Gentianaceae)

Chromosome numbers ranging from n = 17 to n = 42 are reported for 17 of the approximately 30 native species of Centaurium. With few exceptions, the American species are morphologically distinct from the 12 native species of Europe and, as a group, they are also cytologically dissimilar. Diploids (n = 10), known only from the Mediterranean region of southern Europe, have not been found in the Americas. Aneuploidy, which is much less common than euploidy in European species, is almost universal in the American species. Chromosome counts obtained in meiotic pollen mother cells were n = 17 (three species), n = 20 (two species), n = 21 (seven species), n = 22 (two species), n = 36 (two species), n = 40 (one species), n = 41 (one species), n = 42 (one species). Two chromosomal races of n = 21 and n = 22, respectively, were found in one widespread morphological species of Mexico and Central America. The absence of diploids, predominance of aneuploidy and generally higher chromosome numbers in American Centaurium support a conclu- sion that these taxa are derived from ancestral European members of the genus. Centaurium is a moderate-sized genus of the Gentianaceae with about 40-50 species worldwide. It is classified, along with the large genera Gentiarna (ca. 400 species) and Gentianella (ca. 125 species) in the tribe

Irradiation studies on the karyology of charophyta. I. X-rays and gamma-rays.

The present study deals with the effects of X-rays, gamma-rays on the karyology of some selected taxa of charophyta, antheridia having being exposed to radiations. Species of Nitella viz., N. opaca (n=6), N. flagelliformis (n=9) and N. acuminata (n=18) and four of Chara viz., C. fibrosa (n=14), C. globularis var. virgata (n=14), C. setosa (n=28) and C. zeylanica var. diaphora f. oerstidiana (n=42) were employed as experimental materials in various irradiation experiments. X-ray and gamma-ray doses ranged from 100 to 2000 rads. The materials in each case, after exposure to required amount of radiation, were transferred to fresh culture medium and were examined cytologically at varying periods of time. In all experiments controls were maintained.The qualitative changes that were observed in all the taxa with both types of radiations to a greater or lesser extent were: stickiness and of clumping of chromosomes at metaphase and anaphase, chromosome erosion, chromatid gaps, chromosome and chromatid breaks at metaphase and anaphase, anaphase bridges, laggards, unequal grouping of chromosomes, unequal separation, ring chromosomes and rarely, formation of micronuclei.The quantitative estimates of affected cells, based on percentages of those showing chromosome breakage at metaphase and anaphase and cells showing anaphase bridges, showed that levels of radiosensitivity of different taxa differed. The chromosomes of N. opaca having the lowest chromosome number (n=6) and of N. flagelliformis (n=9) with longest chromosomes seem to be more sensitive in comparison to other taxa, while C. zeylanica, with highest chromosome number in the series (n=42) as also with shortest chromosomes, was found to be more radioresistant of all the taxa investigated. However, charophyte taxa in the present study were shown to be more sensitive to radiations as compared with many other algal taxa belonging to other groups investigated earlier. The irradiation studies lend further support to the now more widely held view that Charophyta constitute a very distinctive group amongst algae. The generally held view that algae in general are more resistant to radiations in comparison to higher plants does not seem to apply to the members of Charophyta. On the basis of the present study it has been shown that the chromosomes of N. opaca and N. flagelliformis are as sensitive as to radiations as those of higher plants. The results obtained in the study were adequately discussed.

Cytomorphological Studies in Convolvulaceae

Thirty-one species and varieties of 8 North-Indian Convolvulaceous genera were investigated. Normal diploid like meiotic behaviour was evident in most of these. Polyploid nature of Ipomoea batatas and some desynaptic bivalents in Merremia aegyptia accounted for aberrant meiosis. Some desynaptic bivalents were also observed in I. bonanox, Porana paniculata and Calystegia hederacea.Ipomoea chryseoides (n=15), I. mutabilis (n=15+O-1B), I. dichroa (n=15), I. palmata (white flowered type n=15+1B) and Argyreia campanulata (n=14) represent first chromosome counts for these species. Lowest and highest chromosome numbers n=9 and n=45 were encountered in Jacquemontia pentantha and Ipomoea batatas respectively.Poor incidence of polyploidy may either be due to a meagre cytological coverage or the secondary nature of the high basic numbers met in the family. Aneuploidal relationship of the different species/genera is evident. Importance of aneuploidy and polyploidy in the evolution of Convolvulaceae is discussed.Morphological variability in Ipomoea aquatica, I. eriocarpa, I. fistulosa, I. palmata and I. pestigridis seems to be correlated with the cytological features.

X-Ray Sensitivity of Somatic Cell Hybrids

Different somatic cell hybrids have been studied as a function of their x-ray survival and karyotypic properties. Hybrids between x-ray-sensitive mouse lymphoma cells and mouse fibroblasts, retaining a large proportion of both parental chromosomes, were much more resistant to irradiation than either of the parental cells. On the other hand, hybrids between sensitive mouse lymphoma cells and hamster fibroblasts which also retained a relatively high number of chromosomes from both parents had a sensitivity intermediate between the sensitivities of the parental cell lines. Finally, hybrids between mouse fibroblasts and hamster fibroblasts carrying at least one hamster genome and less than one mouse genome resembled the hamster parent with respect to survival capactity. The significance of these results is discussed.

A novel temperature-sensitive mammalian cell line exhibiting defective prophase progression

A temperature-sensitive mammalian cell line has been isolated which grows and divides normally at the permissive temperature of 33°C. When incubated at 39°C, the nonpermissive temperature, interphase cells continue to enter a prophase-like state. Chromatin-like material condenses and coalesces into dark-staining clumps rather than into discernible chromosomes. Disappearance of the nuclear boundary is observed, but re-formation of the boundary around the clumps fails to occur. Incorporation of labeled precursors reveals a decrease in protein synthesis which is accompanied by a slower decrease in DNA synthesis. Approximately 0.2% of the mutant cells revert in their capability of growth and cell division at 39°C. These “revertants” are found to contain a higher number of chromosomes. The isolation of this mutant is based on the initial observation that the cells become rounded at the nonpermissive temperature. The cell-rounding process characteristic of mitotic cells should serve as a useful marker in the isolation of mitotic mutants.

Satellite DNA and cytogenetic evolution. DNA quantity, satellite DNA and karyotypic variations in kangaroo rats (genus Dipodomys).

The genus Dipodomys (kangaroo rats) exhibits major interspecies variations in the proportions of highly reiterated satellite DNA sequences in the genome as well as in the chromosome number and the proportions of uni-armed and bi-armed chromosomes. For nearly all of the approximately 22 species of the genus and several subspecies, liver DNA was distributed in neutral CsCl buoyant density gradients into four fractions; principal DNA (1.698 g/ml), intermediate-density DNA (1.702 G/ML), MS satellite (1.707 g/ml) and HS (heavy satellites (1.713 g/ml). The total nuclear DNA content of diploid liver cells measured in eleven species by quantitative cytophotometry, ranged from 6.9 to 10.9 pg. These data were correlated with known features of the karotypes of individual species. The salient findings were: (1) that interspecies variations in diploid chromosome number cluster at 52-54, 60-64 and 70-72 (2) that high total nuclear DNA was associated with high chromosome number, and with relatively large amounts of satellite DNA (3) that a high ratio of HS satellites to intermediate-density DNA was generally correlated with a predominance of metacentric and submetacentric chromosomes (high fundamental number). The relationships of satellite DNA to karyotype structure reveal a new level of hierarchy in the genome that appears capable of exerting global control over environmental adaptation and the evolution of new species. This mechanism is consistent with recent hypotheses that changes in the macro-structure of the genome are more important than point mutations in facilitating the rapid phases of animal evolution.

Chromosomes and causation of human cancer and leukemia. XIV. Origin of a large number of markers in a cancer.

A cancerous effusion from a patient with cancer of the breast, with a high modal number of chromosomes (81-83) and with 11-13 abnormal chromosomes (markers) of eight different origins, has been examined in detail karyotypically with C-, G-, and Q-banding techniques. Except for a rare chromosome, all the normal chromosomes were identified and, more importantly, the origin of all markers was ascertained. This study indicates the feasibility of identifying all the chromosomes in cancer cells, even in those with highly polyploid and complicated chromosome constitutions.

Mitotic and Meiotic Chromosomes ofIchthyophis OrthoplicatusTaylor (Amphibia: Gymnophiona)

SUMMARYMitotic and meiotic chromosomes were studied in an Asian caecilian, Ichthyophis orthoplicatus, by a blood culture method and by spermatocyte squashes. For this species, 2N=42, which is the highest chromosome number in the Order Gymnophiona. The karyotype consists of two large metacentrics, one medium-sized submetacentric, three medium-sized metacentrics, two small metacentrics, one small submetacentric, one small subtelocentric, and eleven telocentric microchromosomes. No heteromorphic pair of sex chromosomes is present in either sex. The 21 spermatocyte bivalents have a variable number of chiasmata, positively correlated with chromosome length. The largest bivalent frequently has four or five chiasmata. There are no ring-shaped bivalents. Observations of pachytene bivalents showed a heteropycnotic rod on the end of one arm of bivalent No. 1, and showed that the nucleolus organizer is on chromosome No. 3.If current concepts of caecilian systematics are correct, then primitive caecilians have high numbers of chromosomes including microchromosomes, and advanced caecilians have reduced chromosome numbers and few or no microchromosomes. This same relationship is known for Anura and Urodela. Asian ichthyophiids are karyotypically similar to Asian and African caeciliids, especially in regard to the large-sized and medium-sized chromosome groups. Neotropical species of Caeciliidae and Typhlonectidae seem to have advanced karyotypes compared to Asian and African forms.

Chromosome Number in Gomortega keule

Gomortega keule (Mol.) I. M. Johnston of the monotypic Chilean family Gomortegaceae (Magnoliales sensu lato) has a diploid number of 2n 42. This number, indicating the palaeohexaploid nature of the family, suggests affinities with those magnoliaceous families with similar high basic chromosome numbers, in particular Atherospermataceae, Siparunaceae, and Monimiaceae belonging to the lauralian alliance. Morphological features such as endospermous seeds, valvate anthers, as well as wood anatomy and pollen, accord with this conclusion. Plants referred to Gomortega keule and reported as n = 12, 2n = 24 (Raven et al., 1971), have been redetermined as Bielschmiedia berteroana (Gay) Kostermans (Lauraceae; Raven, 1975). The chromosome number in Gomortega of the monotypic family Gomortegaceae has thus remained unknown until now, and the family is the last in Magnoliales to be counted. The present record thus corrects a past error in the literature and fills a notable gap in the knowledge of cytology in the primitive dicots. MATERIALS AND METHODS Seedlings grown by Dr. Schlegel-Sachs of the Universidad Austral de Chile, from seed collected in the wild, were sent to the Missouri Botanical Garden where root tips were collected from the reestablished plants. Root tips were pretreated in hydroxyquinoline for five hours at room temperature, fixed briefly in 1:3 acetic-ethanol, hydrolyzed in 10% HCl at 600 C for 4 minutes, and squashed in lacto-propionic orcein. Gomortega keule (Mol.) I. M. Johnston. 2n = 42. CHILE. PROV. CONCEPCION: Near Penco, Schlegel-Sachs 6418 (MO).