Genetics and marine pollution

The development of cytogenetic methods applied to cells and tissues of marine invertebrates has been hampered by (1) a lack of in vitro cell lines, (2) inadequate karyotypic information (partly as a result of too few workers chasing too many organisms), and (3) the failure of their chromosomes to band satisfactorily. Compared to mammalian cytogenetics, our knowledge of marine invertebrates lags behind by several decades. With the current concern about mutagens in the marine environment, and the recognition that the cells of marine species have sensitivities to DNA-damaging agents similar to those of higher organisms, there is a need for methods which can be used (a) in environmental monitoring and (b) to screen potentially harmful substances in the laboratory. In the absence of in vitro cell lines, embryos and larvae have been used to provide a supply of dividing cells for mutation studies, although the advent of molecular methods has now brought with it the means to detect DNA damage without any need for the cells to be in a dividing state. Moreover, the use of FISH (Fluorescence In Situ Hybridisation) now makes it possible to study numerical and structural chromosomal aberrations with far greater accuracy than was previously possible. A new marine genotoxicity assay is described, based on the embryos and larvae of a tube-dwelling polychaete worm (Pomatoceros lamarkii), suitable for both laboratory studies and field monitoring. This new Pomatoceros assay provides, at the same time, a useful model for studying the consequences of adult exposure on the offspring. A novel application of marine cytogenetic research is the study of the evolutionary adaptations of invertebrates living in naturally polluted extreme environments viz. deep sea hydrothermal vents, which are typified by high levels of toxic heavy metals and radionuclides, substances known to inflict damage to DNA. Given these new methodological and conceptual advances, it is predicted that our understanding of the role played by mutation in the marine environment, both in an evolutionary and toxicological context, will increase dramatically over the next decade.     

Taxonomic and evolutionary implications of intraspecific variability in chromosome numbers of species of Leucaena Benth. (Leguminosae)

Chromosome numbers were determined in 52 individuals of 14 taxa of Leucaena Benth. from 22 populations. For L. cuspidata and L. kmpirana these are the first published chromosome counts. Intraspecific variability was found for L. lempirana, L. macrophjlta and L. shanonii , and one diploid population of the tetraploid species L. pallida was identified. Comparison of our data with those in the literature showed that for L. collinsii and L. macrophylla there is a relationship between chromosome number and subspecies delimitation. The variability detected in chromosome numbers shows the complexity of the diploid and tetraploid species evolution, and suggests multiple origins for some of the polyploid taxa.     

A Review of Fluorescence in Situ Hybridization (FISH): Current Status and Future Prospects

Fluorescence in situ hybridization (FISH) is a powerful technique for detecting DNA or RNA sequences in cells, tissues and tumors. This molecular cytogenetic technique enables the localization of specific DNA sequences within interphase chromatin and metaphase chromosomes and the identification of both structural and numerical chromosome changes. FISH is quickly becoming one of the most extensively used cytochemical staining techniques owing to its sensitivity and versatility, and with the improvement of current technology and cost effectiveness, its use will surely continue to expand. Here we review the wide variety of current applications and future prospects of FISH technology.     

Chromosome numbers in wild and semidomesticated Brazilian Capsicum L. (Solanaceae) species: do x = 12 and x = 13 represent two evolutionary lines?

Chromosome numbers were determined in 29 accessions of wild and semidomesticated Capsicum species from the EMBRAPA Hortaliças (Brazil) germplasm collection. 2 n  = 24 was found in C. baccatum var. praetermissum , C. chinense , C. flexuosum and C. parvifolium , while C. buforum , C. campylopodium , C. cornutum , C. schottianum , C. villosum var. villosum and five other native south-eastern Brazilian species not yet taxonomically named all had 2 n  = 26 chromosomes. These are the first chromosome number determinations for C. cornutum , C. schottianum , C. villosum var. villosum and the five other Brazilian taxa. Our data confirm published data for C. baccatum var. praetermissum , C. campylopodium , C. chinense , C. flexuosum and C. parvifolium , but not for C. buforum . The prevalence of 2 n  = 26 chromosomes among Brazilian species, along with the morphological and ecological characteristics presented by the wild and semidomesticated species occurring in Brazil, form a pattern different from that found in Andean wild and semidomesticated species. This supports the hypothesis that there are two different evolutionary lines in the genus and that the native south-eastern Brazilian species belong to the ancestral Capsicum gene pool. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 259–269.     

Removal of Stainable Cytoplasmic Substances from Cytogenetic Slide Preparations

A method to remove stainable cytoplasmic substances from cytogenetic preparation using RNase A treatment is reported. The preparations processed with this method are especially useful for the automated analysis of mi-cronuclei of cultured cells with cytochalasin B and of chromosome aberrations induced by radiation.     

Duthieeae,a new tribe of grasses (Poaceae) identified among the early diverging lineages of subfamily Pooideae: molecular phylogenetics,morphological delineation,cytogenetics and biogeography

The phylogeny of Pooideae, one of the largest subfamilies of grasses, has been intensively studied during the past years. To investigate the early evolutionary splits in Pooideae we used a broad sample of genera with uncertain placement, some of which have not been studied in molecular phylogenetics before, complemented by representatives from other lineages of this subfamily. Morphological, cytogenetic and biogeographical analyses were added to the molecular sequence work on chloroplast matK–3’trnK and nuclear ITS. According to chloroplast DNA data, a new and well-supported lineage was identified among the early branches. It consisted of Phaenosperma and a larger group of genera encompassing Anisopogon, Danthoniastrum, Duthiea, Metcalfia, Pseudodanthonia (inclusion resting on ITS and morphology), Sinochasea and Stephanachne. Based on structural characters we suggest to keep Phaenosperma under the monotypic tribe Phaenospermateae and to accommodate the other genera under a new tribe Duthieeae, which is morphologically well-defined by synapomorphic spikelet features. Megalachne and Podophorus were not part of the early diverging Pooideae lineages but belong to the Aveneae/Poeae complex. Morphological characteristics of Duthieeae are discussed with respect especially to Stipeae and reveal consistent differences between both tribes. The genera of Duthieeae and the major lineages of Stipeae are keyed. A cytogenetic survey of exemplary taxa corroborates high chromosome base numbers as prevailing within the early diverging lineages of Pooideae, but chromosome sizes are more highly varied than previously reported. Ecogeographical analyses point to warm and humid conditions as the ancestral bioclimatic niche of Phaenosperma and Duthieeae, whereas adaptation to cold and drought occurred only in a part of Duthieeae but was obviously less successful than in the widespread and much more species-rich tribe Stipeae. The distribution of Duthieeae with species-poor or monotypic genera in mountains of the northern hemisphere and Anisopogon as an outlier in Australia suggests relict character.     

Small Supernumerary Marker Chromosomes and Uniparental Disomy Have a Story to Tell

Small supernumerary maker chromosomes (sSMC) and uniparental disomy (UPD) are rare, and a combination of both is rarely encountered. Accordingly, only 46 sSMC cases UPD have been reported. Despite of its rareness, UPD has to be considered, especially in prenatal cases with sSMC. Here, the authors reviewed all sSMC cases with UPD (sSMC^U+) and compared them to sSMC without UPD (sSMC^U−), which resulted in the following correlations: 1) every sSMC, irrespective of its chromosomal origin, may be principally connected with UPD; 2) mixed hetero- and iso-UPD (hUPD/iUPD) can be observed most often in sSMC^U+ cases followed by complete iUPD, complete hUPD, and segmental iUPD; 3) UPD of chromosomes 6, 7, 14, 15, 16, and 20 is most often reported in sSMC^U+; 4) maternal UPD was approximately nine times more frequent than paternal UPD; 5) if mosaic with a normal cell line, acrocentric-derived sSMC had a three times higher chance of occurrence than the corresponding nonmosaic sSMC cases; 6) UPD in connection with a parentally inherited sSMC is, if existent at all, a rare event; and 7) the gender type and shape of sSMC had no effect on UPD formation. Overall, sSMC^U+ cases may have a story to tell about chromosome number control mechanisms in early embryogenesis.     

Chromosomal abnormalities as a cause of recurrent abortions in Egypt

BACKGROUND:

In 4%-8% of couples with recurrent abortion, at least one of the partners has chromosomal abnormality. Most spontaneous miscarriages which happen in the first and second trimesters are caused by chromosomal abnormalities. These chromosomal abnormalities may be either numerical or structural.

MATERIAL AND METHODS:

Cytogenetic study was done for 73 Egyptian couples who presented with recurrent abortion at Genetic Unit of Children Hospital, Mansoura University.

RESULTS:

We found that the frequency of chromosomal abnormalities was not significantly different from that reported worldwide. Chromosomal abnormalities were detected in 9 (6.1%) of 73 couples. Seven of chromosomal abnormalities were structural and two of them were numerical.

CONCLUSION:

Our results showed that 6.1% of the couples with recurrent abortion had chromosomal abnormalities, with no other abnormalities. We suggest that it is necessary to perform cytogenetic in vestigation for couples who have recurrent abortion.     

Comparative chromosomal analysis and phylogeny in four Ctenomys species (Rodentia, Octodontidae)

A cytogenetic chromosome study was carried out on specimens of four species of Ctenomys – C. talarum, C. rionegrensis, C. pearsoni and C. dorbignyi –from 10 different populations. The analysis of chromosomes was performed through sequential uniform stain, G and C-banding, and with restriction enzymes. The results obtained are discussed in relation to phylogeny. Chromosome evolution in the species studied suggests that the chromosome number has increased due to fissions, and that a reduction of the amount of constitutive heterochromatin has occurred. Different types of heterochromatin, with different patterns, have been added in parallel during evolution. Some taxonomic suggestions can be deduced from this cytogenetic study.     

Qualitative analysis of constitutive heterochromatin and primate evolution

The results of qualitative heterochromatin analysis in 16 species of primates: Homo sapiens , Pan troglodytes and Gorilla gorilla (F. Hominidae), Hylobates syndactilus (F. Hylobatidae), Macaca fascicularis , M. tibetana , Mandrillus sphinx , M. leucophaeus , Cercopithecus aethiops , C. sabaeus and C. albogularis (F. Cercopithecidae), Cebus apella , Ateles belzebuth hybridus , Aotus azarae , Saimiri sciureus and Lagothrix lagothricha (F. Cebidae) are presented in this work. We characterized heterochromatin using: (a) in situ digestion with restriction enzymes AluI, HaeIII, RsaI and Sau3A, and (b) chromosome staining with DA/DAPI on unbanded chromosomes, on C-banded chromosomes and on sequentially G-C-banded chromosomes. The aim of this work was to relate the qualitative characteristics of constitutive heterochromatin observed with the cytogenetic evolutive processes in the primate group. Results obtained show that (1) in the family Cercopithecidae, Papionini species do not present chromosomal rearrangements when their karyotypes are compared and the heterochromatin characteristics are uniform, while Cercopithecini species show a high number of chromosomal reorganizations, but they have the same heterochromatic characteristics; (2) the Platyrrhini species analysed show variability in their karyological and heterochromatic characteristics; (3) the Hominoidea present two different situations: Pan , Gorilla and Homo with few chromosomal reorganizations among their karyotypes but with a high variability in their heterochromatin characteristics, and Hylobates with low heterochromatin variability and a highly derived karyotype. Speciation processes related to chromosome changes and heterochromatin variations in different groups of primates are discussed.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 107–124.