Contributions to the cytotaxonomy of the Commelinaceae. Chromosome evolution in Tradescantia section Cymbispatha

The five species of Tradescantia section Cymbispatha studied, including one species T. poelliae D. R. Hunt, have chromosome numbers of In = 12, 14, 16, 22, 28, 30 and 36 and karyotypes of acrocentric, metacentric or telocentric chromosomes, or mixtures of both acrocentric and metacentric chromosomes. The numbers of major chromosome arms of these cytotypes give a nombre fondamentaP series of 14, 28, 42 and 56 which, in combination with meiotic analyses, indicates plants which, in genetical terms at least, are diploid, tetraploid, hexaploid and octoploid. This series has evolved from a 2 n = 14 acrocentric or telocentric karyotype by a combination of Robertsonian fusion and polyploidy. Pseudo-iso-chromosomes are sometimes formed in this evolutionary development and can persist as stable members of normal complements.     

Multiple sex chromosome system of X1X1X2X2/X1X2)Y type in lutjanid fish, Lutjanus quinquelineatus (Perciformes)

The karyotype and other chromosomal markers as revealed by C-banding and Ag-staining were studied in Lutjanus quinquelineatus and L. kasmira (Lutjanidae, Perciformes). While in latter species, the karyotype was invariably composed of 48 acrocentric chromosomes in both sexes, in L. quinquelineatus the female karyotype had exclusively 48 acrocentric chromosomes (2n = 48) but that of the male consisted of one large metacentric and 46 acrocentric chromosomes (2n = 47). The chromosomes in the first meiotic division in males showed 22 bivalents and one trivalent, which was formed by an end-to-end association and a chiasmatic association. Multiple sex chromosome system of X₁X₁X₂X₂/X₁X₂Y type resulting from single Robertsonian fusion between the original Y chromosome and an autosome was hypothesized to produce neo-Y sex chromosome. The multiple sex chromosome system of L. quinquelineatus appears to be at the early stage of the differentiation. The positive C-banded heterochromatin was situated exclusively in centromeric regions of all chromosomes in both species. Similarly, nucleolus organizer region sites were identified in the pericentromeric region of one middle-sized pair of chromosomes in both species. The cellular DNA contents were the same (3.3 pg) between the sexes and among this species and related species.     

Variation and Evolution in the Karyotype of Lycoris (Amaryllidaceae) V. Chromosomal Variation in L. sanguinea Maxim.

Abstract In 554 bulbs from 38 populations of Lycoris sanguinea , several chromosomal variations have been discovered. Most of the bulbs have a common karyotype consisting of 22 acrocentric ( A ) chromosomes. Though their frequencies are low, some rearranged chromosomes which are aberrant have been found. The aberrants are as follows: 1. Subtelocentrics ( ST ); 2. Telocentrics ( T' ); 3. Metacentrics ( M' ); 4. Very small acrocentrics (a); 5. Very small metacentrics (m); 6. Acentric fragments ( Ac ); and 7. Dicentrics ( Di ) chromosome. All can be easily suspected to be derived from A s. Some aberrations of the satellite chromosomes have been observed also. In addition, a new karyotype composed of 2n=32=31 A + 1 M' chromosomes has been found.     

Genomic changes following the reversal of a Y chromosome to an autosome in Drosophila pseudoobscura

Robertsonian translocations resulting in fusions between sex chromosomes and autosomes shape karyotype evolution by creating new sex chromosomes from autosomes. These translocations can also reverse sex chromosomes back into autosomes, which is especially intriguing given the dramatic differences between autosomes and sex chromosomes. To study the genomic events following a Y chromosome reversal, we investigated an autosome‐Y translocation in Drosophila pseudoobscura. The ancestral Y chromosome fused to a small autosome (the dot chromosome) approximately 10–15 Mya. We used single molecule real‐time sequencing reads to assemble the D. pseudoobscura dot chromosome, including this Y‐to‐dot translocation. We find that the intervening sequence between the ancestral Y and the rest of the dot chromosome is only ～78 Kb and is not repeat‐dense, suggesting that the centromere now falls outside, rather than between, the fused chromosomes. The Y‐to‐dot region is 100 times smaller than the D. melanogaster Y chromosome, owing to changes in repeat landscape. However, we do not find a consistent reduction in intron sizes across the Y‐to‐dot region. Instead, deletions in intergenic regions and possibly a small ancestral Y chromosome size may explain the compact size of the Y‐to‐dot translocation.     

Karyotypic diversification due to Robertsonian rearrangements in Phyllodactylus lanei Smith, 1935 (Squamata, Gekkonidae) from Mexico

We analyzed chromosomes of male and female individuals of Phyllodactylus lanei Smith, 1935 (Squamata, Gekkonidae) from Chamela-Cuixmala Biosphere Reserve, Jalisco state, Mexico. The karyotype constructed for these specimens is composed of 19 pairs of telocentric chromosomes (2n = 38, FN = 38). This karyotype, due to Robertsonian fusions/fissions, differs from the one previously reported in samples from the State of Guerrero, which probably belonged to a different subspecies (2n = 33−34, FN = 40−41). Moreover, a presumed ZW sex chromosome system was not confirmed in the presently studied individuals.      

Contributions to the cytotaxonomy of the Commelinaceae. Chromosome evolution in Tradescantia section Cymbispatha

The five species of Tradescantia section Cymbispatha studied, including one species T. poelliae D. R. Hunt, have chromosome numbers of In = 12, 14, 16, 22, 28, 30 and 36 and karyotypes of acrocentric, metacentric or telocentric chromosomes, or mixtures of both acrocentric and metacentric chromosomes. The numbers of major chromosome arms of these cytotypes give a nombre fondamentaP series of 14, 28, 42 and 56 which, in combination with meiotic analyses, indicates plants which, in genetical terms at least, are diploid, tetraploid, hexaploid and octoploid. This series has evolved from a 2 n = 14 acrocentric or telocentric karyotype by a combination of Robertsonian fusion and polyploidy. Pseudo-iso-chromosomes are sometimes formed in this evolutionary development and can persist as stable members of normal complements.     

Variations in flavonoid patterns within the genus Chondropetalum (restionaceae)

HPLC and chemical analyses of the flavonoids in culms of 11 Chondropetalum species divide the genus into two groups: seven, with glycosides of myricetin larycitin and syringetin; and four, with glycosides of kaempferol, quercetin, gossypetin, gossypetin 7-methyl ether and herbacetin 4′-methyl ether. This chemical dichotomy is correlated with anatomical differences and confirms the view that the genus requires taxonomic revision. HPLC measurements on those species with myricetin derivatives show that taxa with a qualitatively similar pattern of glycosides can be readily separated on quantitative grounds. Syringetin 3-arabinoside and a glycoside of herbacetin 4′-methyl ether are reported for the first time from the genus.     

Studies in individual spawnings of Salmo salar: a model to explain chromosome polymorphism patterns

Summary Atlantic salmon fry from nine offspring belonging to individual spawnings were karyotyped. Different patterns of Robertsonian chromosome polymorphism were obtained. A theoretical model is developed to explain the different chromosome polymorphism patterns in Salmo salar offspring in terms of the chromosome numbers of the parents.     

Radiation-induced cytogenetic damage in relation to changes in interphase chromosome conformation

The premature chromosome condensation (PCC) technique was used to study several factors that determine the yield of chromosome fragments as observed in interphase cells after irradiation. In addition to absorbed dose and the extent of chromosome condensation at the time of irradiation, changes in chromosome conformation as cells progressed through the cell cycle after irradiation affected dramatically the yield of chromosome fragments observed. As a test of the effect of chromosome decondensation, irradiated metaphase Chinese hamster ovary (CHO) cells were allowed to divide, and the prematurely condensed chromosomes in the daughter cells were analyzed in their G1 phase. The yield of chromosome fragments increased as the daughter cells progressed toward S phase and chromosome decondensation occurred. When early G1 CHO cells were irradiated and analyzed at later times in G1 phase, an increase in chromosome fragmentation again followed the gradual increase in chromosome decondensation. As a test of the effect of chromosome condensation, G0 human lymphocytes were irradiated and analyzed at various times after fusion with mitotic CHO cells, i.e., as condensation proceeded. The yield of fragments observed was directly related to the amount of chromosome condensation allowed to take place after irradiation and inversely related to the extent of chromosome condensation at the time of irradiation. It can be concluded that changes in chromosome conformation interfered with rejoining processes. In contrast, resting chromosomes (as in G0 lymphocytes irradiated before fusion) showed efficient rejoining. These results support the hypothesis that cytogenetic lesions become observable chromosome breaks when chromosome condensation or decondensation occurs during the cell cycle.     

Unprecedented chromosomal diversity and behaviour modify linkage patterns and speciation potential: structural heterozygosity in an Australian spider

The Huntsman spider Delena cancerides shows an extraordinary level of chromosomal diversity and meiotic complexity. Some populations form normal bivalents at male meiosis, but 14 populations form chains of chromosomes. Six of these populations form two chains, and so show segregation behaviour which is beyond our current understanding of meiotic processes. Chromosomal variation of this sort is rarely tolerated in other species, because the segregation of long chromosome chains frequently results in gametes with too many or too few chromosomes. The resulting reproductive failure may form the basis for reproductive isolation in many species, and so the mechanisms that allow D. cancerides to segregate long chromosome chains have allowed this species to maintain cohesion despite extensive chromosomal variation over its range. The effect these chromosome chains have on the population genetics of the species is discussed, and a model for the evolution of the system is proposed.     

Embryogenesis and the production of males by apterous viviparae of the green peach aphid Myzus persicae in relation to photoperiod

Apterous viviparae of a holocyclic strain of Myzus persicae were given various numbers of prenatal and postnatal exposures to male-inducing, long-night scotophases (15 hr darkness per diem). The sex of the embryos in various positions within their ovarioles was determined from chromosome preparations and correlated with the sequence with which female and male larvae were deposited. An abnormal follicle was found frequently between the female and male embryos in the ovarioles of aphids raised under long nights.Apterous viviparae exposed to long nights from birth or earlier usually produced several females and then switched over to exclusive male production. The more prenatal exposures to long nights given to the aphids, the fewer females were deposited by them and the earlier they started to produce males. When apterae were continuously exposed to long nights from 2 days or more before their birth, some, and occasionally all, their ovarioles were solely androparous. In general, male-producing apterae deposited considerably fewer larvae (female as well as male) than apterae that produced females exclusively. The 1–2 day pause in larviposition that typically occurs between the deposition of the female and male larvae was attributed to a slower rate of development of the male embryos. The results are discussed in relation to the hormonal changes that may be induced by the photoperiodic treatments.     

The 520 nm absorbance changes in Scenedesmus obliquus and its relation to Photosystem I

The kinetics (region of seconds) of the light-induced 520 nm absorbance change and its dark reversal have been studied in detail in the wild type and in some pigment and photosynthetic mutants of Scenedesmus obliquus. The following 5 lines of evidence led us to conclude that the signal is entirely due to the photosystem I reaction modified by electron flow from Photosystem II.Gradual blocking of the electron transport with 3(3,4-dichlorophenyl)-1,1-dimethylurea resulted in diminution and ultimate elimination of the biphasic nature of the signal without reducing the extent of the absorbance change or of the dark kinetics. On the contrary, blocking electron flow at the oxidizing side of plastoquinone with 2, $\text{5-}\text{dibromo}\text{-3-}\text{methyl}\text{-6-}\text{isoprophyl}\text{-p-}\text{benzoquinone}$ or inactivating the plastocyanin with KCN, prolonged the dark reversal of the absorbance change apart from abolishing the biphasic nature of the signal.Action spectra clearly indicate that the main signal (I) is due to electron flow in Photosystem I and that its modification (Signal II) is due to the action of Photosystem II.Signal I is pH independent, whereas Signal II demonstrates a strong pH dependence, parallel to the O₂-evolving capacity of the cells.Chloroplast particles isolated from the wild type Scenedesmus cells demonstrated in the absence of any added artificial electron donor or acceptor and also under non-phosphorylation conditions the 520 nm absorbance change with approximately the same magnitude as whole cells. The dark kinetics of the particles were comparatively slower. Removal of plastocyanin and other electron carriers by washing with Triton X-100 slowed down the kinetics of the dark reversal reaction to a greater extent. A similar positive absorbance change at 520 nm and slow dark reversal was also observed in the Photosystem I particles prepared by the Triton method.Mutant C-6E, which contains neither carotenoids nor chlorophyll $\text{b}$ and lacks Photosystem II activity, demonstrates a normal signal I of the 520 nm absorbance change. This latter result contradicts the postulate that carotenoids are the possible cause of the 520 nm absorbance change.     

Chromosomal Variation in Lotus alpinus (Fabaceae)

Abstract An accession of Lotus alpinus Schleich. (2n=2x=12) from Turkey in which B chromosomes have been found was studied morphologically and karyologically. Chromosome numbers were observed in 519 cells from nine plants which all exhibited mixoploidy (2n=11, 12, 12 + 1B, 12 + 2B and over 20). Keel tip color, stem pubescence, and inflorescence size differed from a collection of this species from Switzerland. While the percentage of total lengths of the chromosome complements and the relative chromosome lengths in the two accessions were very similar, the total complement lengths differed considerably (23.14μm Turkey vs. 29.46μm Switzerland). This karyological difference is not considered to be the result of the presence of B chromosomes, but probably the result of hybridization between different genotypes. Aborted seed pods were observed which lent credibility to this hypothesis. Plants of this accession may have arisen as a result of hybridization between Lotus corniculatus and/or L. alpinus as both diploid and tetraploid cytotypes are reported in the Turkey collection for these species. The data would lend support for their hybrid origin.     

Leaf flavonoids of Glycine subgenus Glycine in relation to systematics

A survey of leaf flavonoids and isoflavonoids in several taxa of the genus Glycne subgenus Glycine was undertaken to see if this would help interpret inter- and intraspecific relationships in the genus. C-Glycosylflavones based on apigenin were found in Glycine tomentelia, G. tabacina and G. falcata. Glycosides of quercetin and kaempferol were also detected in G. tabacina. In the cultivated soybean, G. max, and its wild annual relative, G. soja, only quercetin and kaempferol glycosides have been reported. Interspecific hybrids of Glycine species sometimes show additive flavonoid patterns in F₁ hybrid leaf tissue. All perennial wild species analysed including Glycine canescens and G. latifolia have the isoflavonoids genistin (genesitein 7-O-glucoside), daidzein and coumestrol in the leaves.     

A supernumerary “B-sex” chromosome drives male sex determination in the Pachón cavefish,Astyanax mexicanus

1. Download : Download high-res image (219KB)
2. Download : Download full-size image

     

On the induction of chromosome structural changes by hydroxylamine in Vicia faba

Primary roots of a new karyotype of Vicia faba with all chromosomes inter-distinguishable have been used to study the induction by hydroxylamine hydrochloride (HA) of chromatid aberrations and their intrachromosomal distribution. HA induced both chromatid intra- and interchanges of the delayed type. The effectiveness of HA increased with increasing temperature and was dependent on the pH during treatment (more aberrations at pH 7.5 as compared with 4.8). The frequency of incomplete reunion was markedly higher after HA treatment than after treatment with maleic hydrazide (MH) or ethanol. In combined treatments, HA reduced the reunion involvement in HA-induced aberrations of certain chromosome segments was found and compared with distribution patterns of chromatid aberrations after treatment with MH and ethanol. Data and hypotheses concerning possible modes of action of HA eventually resulting in chromosome structural changes are discussed. It is concluded that alterations of the cytosine moiety in chromosomal DNA are not responsible for chromosomal damage induced by HA.     

A method to generate microcells from human lymphoblasts for use in microcell mediated chromosome transfer

Summary A method is described to generate microcells from human lymphobalsts for use in microcell-mediated chromosome transfer (MMCT). Micronuclei were induced in cells from a human lymphoblastic cell line by prolonged colcemid treatment, and were separated from these lymphoblasts by: (a) attaching the cells to Concanvalin A coated plastic slides designed for enucleation, and (b) centrifuging the slides in medium containing cytochalasin B. Microcells of less than 3 μm in diameter were fused with thymidine kinase negative mouse fibroblast (LMTK⁻). HAT medium (hypoxanthine, aminopterin and thymidine) was used to select microcell hybrids expressing thymidine kinase activity. Positive clones were isolated and Q-banded for chromosome analysis. Unlike previous methods this procedure permits microcells to be easily generated from lymphoid cells. This methodology of enucleation of microcells may be extended to a variety of other donor cell types which can be micronucleated but which do not adhere tightly to enucleation slides and do not exhibit extrusion subdivision. This feature makes our methodology particularly useful for constructing a library of hybrid clones containing one or a few human chromosomes.