Check-list of chromosome numbers of the family Hygromiidae (Gastropoda: Stylommatophora) with new data on Circassina frutis

Chromosome number data on the Hygromiidae (Gastropoda: Stylommatophora) are summarized and reviewed briefly in the context of the phylogeny of the family. In hygromiids, the haploid chromosome numbers range from 21 to 26. It is supposed that n = 21 is the ancestral chromosome number in the family. The modal haploid number for Hygromiidae is 23. Description of karyotype in terms of chromosome number and morphology of hygromiid land snail Circassina frutis is provided for the first time. The diploid chromosome number of this species is 2n = 46. The karyotype is symmetric and consists of 21 pairs of metacentric and 2 pairs of submetacentric chromosomes. The karyotype formula is as follows: 2n = 42m + 4sm (n = 21m + 2sm). The fundamental number (FN) is 92. Chromosomes range in length from 2.53 μm for the smallest pair to 6.00 μm for the largest pair. The total length of chromosomes in diploid complement (TCL) is 170.40 ± 3.22 μm.

Role of chromosomal instability in cancer progression

Cancer cells often displaychromosomal instability(CIN), a defect that involves loss or rearrangement of the cell’s genetic material – chromosomes – during cell division. This process results in the generation of aneuploidy, a deviation from the haploid number of chromosomes, and structural alterations of chromosomes in over 90% of solid tumours and many haematological cancers. This trait is unique to cancer cells as normal cells in the body generally strictly maintain the correct number and structure of chromosomes. This key difference between cancer and normal cells has led to two important hypotheses: (i) cancer cells have had to overcome inherent barriers to changes in chromosomes that are not tolerated in non-cancer cells and (ii) CIN represents a cancer-specific target to allow the specific elimination of cancer cells from the body. To exploit these hypotheses and design novel approaches to treat cancer, a full understanding of the mechanisms driving CIN and how CIN contributes to cancer progression is required. Here, we will discuss the possible mechanisms driving chromosomal instability, how CIN may contribute to the progression at multiple stages of tumour evolution and possible future therapeutic directions based on targeting cancer chromosomal instability.

Comparative Karyotype Analysis Of Slugs Of The Genus Arion (Gastropoda, Pulmonata, Arionidae)

Karyotypes of four species of the genus Arion were investigated, namely, A. distinctus (2n = 48m + 8sm = 56; FN = 112), A. lusitanicus s. l. (2n = 4 4m + 6 sm + 2st = 52; FN = 104), A. fuscus (n = 26, 2n = 52, FN = 104) and A. fasciatus (n = 29, 2n = 58, FN = 116). The karyotype of A. lusitanicus s. l. was identical to those of A. fuscus, A. ater and A. rufus. The karyotype of A. fasciatus in the haploid number of chromosomes is identical to another close species — A. circumscriptus (n = 29) from the United Kingdom. The identical number of chromosomes in species of the subgenus Arion (A. lusitanicus s. l., A. ater, A. rufus) and species of the subgenus Mesarion (A. fuscus) (n = 26) may be a reason for their merging.

Cytotaxonomy of Simulium (Montisimulium) ghoomense (Diptera: Simuliidae) from the Darjeeling Hills, India

The polytene chromosomes are mapped for a scarce Himalayan simuliid, Simulium (Montisimulium) ghoomense Datta, from the Darjeeling area of India. This species has three tightly paired polytene chromosomes with a haploid number of 3. Chromosomes I, II, and III account for 39.6%, 30.3%, and 30.1% of the total complement length, respectively. The centromeres of chromosomes II and III consistently form a putative partial chromocenter. Sex chromosomes are undifferentiated and polymorphisms and sibling species are lacking in a sample of 35 larvae. This is the first chromosomal map for a species in the subgenus Montisimulium in India.

Karyological and endosymbiotic notes on two Choricystis species (Trebouxiophyceae, Chlorophyta)

Two species of the genus Choricystis (Choricystis minor and Choricystis chodatii) have been chromosomally surveyed. In addition, their ability to form symbiotic associations with the ciliate Paramecium bursaria was also investigated. Choricystis minor (clone #8931/1 from strain #8931) was isolated from a moss sample collected on Livingston Island, Maritime Antarctica. Choricystis chodatii (clone #3090/1) was derived from strain #3090 Chodat-type culture (loc. Switzerland, lake Geneva). The karyotypes of both species showed a haploid number of five chromosomes and shared some similarity in the chromosome lengths. The absolute chromosome lengths ranged from 1.25 µm to 2.95 µm. Studied species possess equal abilities for endosymbiotic associations with Paramecium bursaria. Descriptions of the species and a short discussion on their taxonomical status are given.

CHROMOSOME STUDIES IN TURKISH SPECIES OF NONEA (BORAGINACEAE): THE ROLE OF POLYPLOIDY AND DESCENDING DYSPLOIDY IN THE EVOLUTION OF THE GENUS

Seven Turkish species of Nonea Medik. (Boraginaceae-Boragineae) were studied karyologically using material collected in the field from wild populations. Somatic chromosome number and karyotype morphology were determined for each species using orcein staining. Nonea pulmonarioides is diploid with 2n=20, though some cells showed 2n=19. Nonea anchusoides turned out to be tetraploid with 2n=4x=40, while N. macrosperma was characterized by a hexaploid complement of 2n=6x=60. These data indicate polyploidy based on x=10 as a major mechanism of speciation in the perennial members of the genus. Among the annuals, N. echioides and N. versicolor showed 2n=16, while N. obtusifolia and N. lutea were characterized by 2n=20 and 2n=14, respectively. The results reveal that x=10 is more frequent in Nonea than previously realized, and that it may be the ancestral haploid number of diploid endemics of (sub)alpine habitats in the Pontic-Caucasian mountain system. The hypothesis is here proposed that the base numbers x=9, x=8 and x=7, progressively prevalent in the annual species from lower altitudes, may have originated through descending dysploidy associated with the tendency to shorten the life cycle as an adaptation to arid habitats.

The kariotype of the parasitoid Chelonus insularis Cresson (Hymenoptera, Braconidae, Cheloninae)

The karyotype of Chelonus insularis (Hymenoptera, Braconidae, Cheloninae) is described. The males show an haploid number of seven chromosomes and the females a diploid number of fourteen chromosomes, confirming haplo-diploid sex determination. Comparisons of these results with karyotypes of other species of the same family were done and a possible mechanism involved in the karyotype evolution of this species is discussed.

Karyotypic analysis of Polymyxa graminis (Plasmodiophoromycetes) based on serial sections of synaptonemal complexes

Three pachytene nuclei of Polymyxa graminis Ledingham were reconstructed from serial thin sections. Thirty synaptonemal complexes (SCs) were counted, indicating the identical haploid number (30) that was reported for Polymyxa betae. SCs of P. graminis and P. betae were similar in structure, and nuclear volumes and total lengths of SCs per nucleus were not significantly different for the two species.