Telocentric Pairs Research Articles

Comparative Karyological Studies and Shell Measurements of Two Egyptian Marine Species of Genus Cerithium (Prosobranchiata-Gastropoda).

Cerithium adustum and Cerithium nodulosum collected from the rocky shore on the Red Sea were karyotyped. These two species showed a distinct differentiation in the diploid chromosome number (2n=18 and 16 respectively). The karyotype of Certhium adustum consists of: six metacentric pairs and three submetacentric pairs while the karyotype of C. nodulosum consists of: two metacentric pairs, three submetacentric pairs and three telocentric pairs. Shell measurements of these species are also described in details in this paper. These results are reported for the first time in Egypt.

Karyotypes of three species of marine catfishes from Brazil

The chromosomes of three species of fishes belonging to the family Ariidae -Netuma barba, Genidens genidens and Amis parkeri - were studied after conventional Giemsa staining. All three species have a diploid chromosome number of 2n = 56. The karyotype comprises 18 metacentric (m), 18 submetacentric (sm), 18 subtelocentric (st) and 2 telocentric (t) pairs for N. barba; 12 m, 20 sm, 20 st and 41 pairs for G. genidens; 16 m, 16 sm, 22 st and 21 pairs for A. parkeri. The results obtained from these three species are compared with each other and with those found in literature.

Karyotype of Lasaea australis, a brooding bivalve species

Karyological investigations have been carried out on the only known cross-fertilizing Lasaea species, L. australis, a marine brooding bivalve with a pelagic larval development. The karyotype consists of 18 pairs of chromosomes (2n = 36), including four metacentric, six submetacentric, three subtelocentric and five telocentric pairs. Comparison with other known Lasaea karyotypes shows that L. australis can be considered as ancestral, and its asexual and direct-developing congeners are characterized by mechanisms of polyploidy.

KARYOTYPES OF FIVE SUBANTARCTIC BIVALVE SPECIES

Chromosomes of five subantarctic species were studied from mitotic metaphases using cell suspension techniques. Among the Protobranchia, Malletiagigan-lea has a diploid chromosome number of 2n = 38 with five metacentric, seven submetacentric, five sub-telocentric and one telocentric pairs, and Yoldia (Aequiyoldia) woodwardi also shows 2n = 38 but with ten metacentric, six submetacentric and three sub-telocentric pairs. Among the Lamellibranchia, the pterioidan Limatula pygmaea has 2n = 38 with six metacentric, eleven submetacentric and two sub-telocentric pairs, the veneroidan Cyclocardia astar-toides has 2n = 30 with five metacentric and ten telocentric pairs and the anomalodesmatan Laternula elliptica has 2n = 40 with two metacentric, one submetacentric, two subtelocentric and fifteen telocentric pairs. Our results indicate that in all the Nuculoidea studied so far, a diploid number of 2n = 38 has been found. In addition, the karyotypes show a close overall appearance in relative lengths with a majority of meta-centric-submetacentric chromosomes. The species differ in the proportion of the different morphological types of chromosomes. In the Lamellibranchia, each species corresponds to a particular case within their respective orders (Pterioida, Veneroida, Anomalodesmata).

Studies on the Chromosomal Analysis and Shell Measurements of Two Species, Bellamya unicolar and Lanistes bolteni(Prosobranchiata: Gastropoda).

Chromosomes were counted in the preparations of gonad tissues from the two species Bellamya unicolor and Lanistes bolteni collected from different localities around Qena City in Upper Egypt. A basic diploid chromosome number of 18 and 26 were presented in Bellamya unicolor and Lanistes bolteni, respectively. The karyotype of Bellamya unicolor consists of: five metacentric pairs, two submetacentric pairs and two subtelocentric pairs, while the karyotype of Lanistes bolteni consists of: eight metacentric pairs two subtelocentric pairs and three telocentric pairs. Shell measurements for these two species are also described in details in this paper. These results are reported for the first time in Egypt.

Number and Morphology of The Metaphase Mitotic Chromosomes inScrobicularia Plana(Da Costa, 1778) (Mollusca, Bivalvia, Tellinacea)

SUMMARYA diploid number of 38 chromosomes has been determined on preparations made with cell suspension from gill and labial palps of Scrobicularia plana, a member of the Scrobiculariidae of the French Atlantic coast. An average karyotype was obtained by measuring and arranging the chromosomes of 15 mitotic metaphase plates. The 19 pairs could be grouped in 6 pairs of metacentrics, 5 pairs of submetacentrics, 7 pairs of subtelocentrics and 1 pair of telocentrics, giving a fundamental number of 60. The karyotype is characterized by mean chromosomic absolute lengths comprised between 3.23 and 5.71 μm and a total chromosomic length of 158.26 μm. Two original features have been observed: the presence of metaphase plates with 39 chromosomes which seem to be the result of the breakage of a large metacentric into two small telocentrics and a giemsa-negative region on the long arm of one chromosome of the third pair of metacentrics.

Chromosome studies in pelagic opisthobranch molluscs

Chromosome number and morphology were studied in nine species of pelagic opisthobranchs ("pteropods"). Among Thecosomata, seven species were investigated. Limacina inflata has a diploid chromosome number of 2n = 20 with metacentric and submetacentric chromosome pairs. Creseis acicula has 2n = 20 (five metacentric and five submetacentric pairs). Creseis virgula has 2n = 20 (seven metacentric, one submetacentric, one subtelocentric – submetacentric, and one submetacentric – subtelocentric pair). Clio pyramidata has 2n = 22 (five metacentric, one submetacentric, two submetacentric – subtelocentric, two subtelocentric, and one telocentric pair). Cavolinia inflexa has 2n = 24 (six metacentric, one submetacentric, two subtelocentric – submetacentric, one subtelocentric – telocentric, and two subtelocentric pairs). Peraclis reticulata has 2n = 24 (six metacentric and six submetacentric or subtelocentric pairs). Cymbulia peroni has 2n = 34 (six metacentric, three submetacentric, seven subtelocentric, and one telocentric pair). Among Gymnosomata, two species were investigated. Pneumodermopsis canephora has 2n = 32 (two metacentric, three submetacentric, four submetacentric – subtelocentric, one subtelocentric – submetacentric, five subtelocentric, and one telocentric – subtelocentric pair). Pneumoderma atlanticum has 2n = 32 (three metacentric, five submetacentric, four submetacentric – subtelocentric or subtelocentric – submetacentric, and four subtelocentric pairs). For three of the nine pteropod species, material was abundant enough to permit staining for the nucleolar organizer region. This region occurred on pair 9 in Creseis acicula, on pair 6 in Cavolinia inflexa and on pair 2 in Pneumodermopsis canephora. Results on number, morphology, and size of the chromosomes of each of the studied species are discussed. The present chromosomal evidence confirms the separation, sometimes seen as controversial, of the pelagic opisthobranchs into the orders Thecosomata and Gymnosomata. The Thecosomata constitute an isolated order among opisthobranchs by their striking chromosomal diversity. In contrast, the Gymnosomata show cytogenetic features that suggest an evolutionary trend with plesiomorphic characters, as in the Anaspidea and Sacoglossa.

Karyotypes of two rare species of hynobiid salamanders from Taiwan, Hynobius sonani (Maki) and Hynobius formosanus Maki (Urodela)

Two salamanders endemic to Taiwan, Hynobius sonani and Hynobius formosanus, are similar to Japanese hynobiids in having 2n = 58 chromosomes and by the absence of a medium-sized telocentric pair. H. sonani has 6 metacentric and 10 telocentric microchromosome pairs, while H. formosanus has 5 metacentric and 11 telocentric microchromosome pairs. The karyotype of H. sonani is nearly identical to that of the Japanese hynobiid salamander H. boulengeri. Karyophylogenetic relationships among forms of mountain-stream type hynobiids of Taiwan and Japan are discussed.

The karyotype of Hynobius takedai M. Matsui et Miyazaki, 1984, with comments on the karyotypic relationships among japanese salamanders of the genus Hynobius.

We have examined the chromosomes of Hynobius takedai. The karyotype (2n=56) is characterized by the absence of a medium-sized telocentric pair and, in this respect, H. takedai resembles the forms from northeastern Japan (H. lichenatus from Iwate Pref., H. nigrescens, and northern populations of H. tokyoensis) but differs from southwestern forms (H. abei, H. nebulosus and southern population of H. tokyoensis). H. takedai is also distinct from all previously studied species in the presence of 6 meta- or submetacentric and 9 telocentric microchromosome pairs. Karyotypic relationships among forms of the lichenatus and nebulosus groups are discussed.

Chromosome studies in species and hybrids ofPetrorhagia sect.Kohlrauschia (Caryophyllaceae)

Cytogenetic investigations have been made in the fourPetrorhagia species and hybrids of the sectionKohlrauschia. The three diploid species show close similarities in chromosome number, size and morphology, with the exception ofP. velutina, where one pair of metacentric chromosomes is represented by a pair of telocentrics. Meiotic studies in hybrids indicate close genomic homology between the diploid species and also between the two floral forms ofP. prolifera. The tetraploidP. nanteuilii behaves as an allotetraploid forming only bivalents at meiosis and results suggest thatP. velutina andP. prolifera are the diploid progenitors of this species. Since meiosis in diploid and triploid hybrids results in extensive intergenomic pairing it is concluded that the natural tetraploid has a bivalent promoting mechanism that prevents pairing between the genomes of its diploid progenitors.

Karyotypic studies inGarra lamta andMystus cavassius (Pisces)

Karyomorphological studies were made on males ofGarra lamta (Fam : Cyprinidae) and on both sexes ofMystus cavassius (Fam : Bagridae) from their kidney metaphase complements.Garra lamta had 2n = 50 chromosomes alignable into 25 homomorphic pairs comprising 3 pairs of metacentrics, 9 pairs of submetacentrics, 6 pairs of subtelocentrics and 7 pairs of telocentrics (NF = 86).Mystus cavassius had 2n = 58 chromosomes in both sexes and their karyotypes revealed 29 pairs of homomorphic chromosomes consisting of 7 pairs of metacentrics, 13 pairs of submetacentrics, 2 pairs of subtelocentrics and 7 pairs of telocentrics (NF = 102). No sex chromosome was identifiable in any sex of the two species.

Karyotypic anomalies in indian house rat, Rattus rattus rufescens Gray.

The diploid chromosome number in the common house rat of Allahabad, Rattus rattus rufescens Gray., is 42 with XX/XY sex determining mechanism. The autosomes consists of 13 pairs of telocentrics (T or t) and 7 pairs of metacentrics (M or m). X is a medium-size, telocentric (T), ranking 5th or 6th in the order of length, in the complement, and constitutes 5.55 % of the total haploid length. Y is variable in size. Several karyotypic anomalies, such as the presence of an unpaired, large Sin or T chromosome, heteromorphic pair 1, close association of one of the homologues each of pairs 7 and 4, 7 and 12 and pair I and a large telocentric chromo-some, are reported.

Autosomal polymorphism in albino rats, Rattus norvegicus, Berkenhout.

Karyotype of Rattus norvegicus, Berkenhout from Indian environs is reported for the first time. The diploid number is found to be 42 with XX/XY sex determining mechanism X is a medium telocentric chromosome ranking 6th or 7th in order of size and constitutes 5.45% of the total haploid set. The size of the Y is found to be variable. It is either the smallest telocentric or equal to the medium size telocentric pair 11 of the group A of our classification. Chromosome polymorphism involving chromosome pairs No. 9, 12 and 13 is reported.

Chromosome Complements of the Mediterranean Mullets (Pisces Perciformes)

SUMMARYThe karyotypes of six species of Mediterranean mullets have been studied: Mugil cephalus, Liza aurata, Liza saliens, Liza ramada, Chelon labrosus and Oedalechilus labeo. The diploid number in all these species is 2n=48. On the basis of the morphology of the karyotype, 3 cytotaxonomic groups are proposed: a) Mugil cephalus, all the chromosomes of which are acrocentric; b) Liza and Chelon with one pair of subtelocentrics; c) Oedalechilus with one pair of telocentrics with a very small arm. The karyologic finding is discussed with regard to the position of the Mugilidae in systematic studies.

Heterochromatin and disproportionate chromosome replication in Anatopynia dyari (Diptera: Chironomidae).

Salivary gland chromosomes from four populations of Anatopynia dyari were examined together with mitotio and meiotic chromosomes from one of the sites. Both mitotic and meiotic cells possess large blocks of heterochromatin, some of which fluoresce brightly after quinacrine staining. Mitotic figures show twelve chromosomes consisting of a graded size series with 5 meta- and submetacentric pairs and one small telocentric pair. — Salivary gland chromosomes have a loose chromocentre and three distinct size classes of chromosomes. The size classes include 1 long metacentric, 4 medium acrocentrics and 1 very small telocentric which is also twice the thickness of the rest of the complement. Quinacrine staining produces bright fluorescence of the centromeric third of chromosome VI, some ectopically paired regions of the chromocentre, basal bands and the telomeres of some chromosomes. — The discrepancy between arm ratios and relative lengths of mitotic and polytene chromosomes is explained by under-replication of nonfluorescing heterochromatin in the latter case. Brightly fluorescing heterochromatin behaves in an anomalous manner suggesting that it is either over, or else not severely under-replicated in salivary glands. The extra thickness of chromosome VI also suggests that it undergoes an extra round of replication. — A common complex rearrangement was found in the long arm of chromosome III in three of the populations. In the one population tested it was in Hardy Weinberg equilibrium.

Chromosomes of Richardiidae, Otitidae and Platystomatidae (Diptera: Acalyptratae)

Descriptions of the chromosome complements of one species of the Richardiidae, ten of the Otitidae and nine of the Platystomatidae, are added in this report to the two for Otitidae provided by Metz (1916). The 2n = 10 complement of the single Richardiidae species had a total complement length (TCL) of 68.7μ. Complements of the 12 Otitidae species ranged from 2n = 6 to 12 and averaged 45.8μ in TCL whereas those of nine Platysiomatidae ranged from 2n = 6 to 12 and averaged 41.4μ in TCL. Morphological differences between complements having the same chromosome number are discussed. A karyotype having a short telocentric sex pair and five meta-to submetacentric autosomal pairs constitutes a common karyological feature and could be the basic (primitive) karyotype of species of Acalyptrate and Calyptrate Diptera. It is suggested that the basic 2n = 12 complements of Drosophila species (10 rods and 2 dots) may be far from typical for species of such Diptera.

Somatic association of telocentric chromosomes carrying homologous centromeres in common wheat

Measurements of distances between telocentric chromosomes, either homologous or representing the opposite arms of a metacentric chromosome (complementary telocentrics), were made at metaphase in root tip cells of common wheat carrying two homologous pairs of complementary telocentrics of chromosome 1 B or 6 B (double ditelosomic 1 B or 6 B). The aim was to elucidate the relative locations of the telocentric chromosomes within the cell. The data obtained strongly suggest that all four telocentrics of chromosome 1 B or 6 B are spacially and simultaneously co-associated. In plants carrying two complementary (6 B (S) and 6 B (L)) and a non-related (5 B (L)) telocentric, only the complementary chromosomes were found to be somatically associated. It is thought, therefore, that the somatic association of chromosomes may involve more than two chromosomes in the same association and, since complementary telocentrics are as much associated as homologous, that the homology between centromeres (probably the only homologous region that exists between complementary telocentrics) is a very important condition for somatic association of chromosomes. The spacial arrangement of chromosomes was studied at anaphase and prophase and the polar orientation of chromosomes at prophase was found to resemble anaphase orientation. This was taken as good evidence for the maintenance of the chromosome arrangement - the Rabl orientation - and of the peripheral location of the centromere and its association with the nuclear membrane. Within this general arrangement homologous telocentric chromosomes were frequently seen to have their centromeres associated or directed towards each other. The role of the centromere in somatic association as a spindle fibre attachment and chromosome binder is discussed. It is suggested that for non-homologous chromosomes to become associated in root tips, the only requirement needed should be the homology of centromeres such as exists between complementary telocentrics, or, as a possible alternative, common repeated sequences of DNA molecules around the centromere region.

Chromosome Variation in North American Fence Lizards (Genus Sceloporus; Undulatus Species Group)

Cole, Charles J. (Dept. of Herpetology, American Museum of Natural History, Central Park West at 79th Street, New York 10024) 1972. Chromosome variation in North American Fence Lizards (Genus Sceloporus; undulatus species group). Syst. Zool. 21:357-363.Five species of lizards in the undulatus species group of the genus Sceloporus have generally similar karyotypes with a diploid number of 22 chromosomes. Nevertheless, extensive variation occurs in centromere position on pair number 7. Comparisons of chromosomes in population samples from numerous localities across North America reveal considerably more variability and kocal differentiation than is expected on the basis of current taxonomy. Intraspecific and intrasubspecific differences within the species S. undulatus often are greater than interspecific differences. Within most local populations, however, 7 occurs in a fixed (homozygous) state, as a metacentric, submetacentric, subtelocentric, or telocentric pair. Thus, individually recognizable chromosomes occurring in lizards in adjacent populations can serve as genetic markers to document interbreeding between distinctive chromosome races and improve our understanding of the evolution, systematics, and population genetics of these terrestrial vertebrates. [Sceloporus; chromosomes.] Fence lizards are well-known reptiles that abound in much of the United States and Mexico. These species and their closest relatives comprise the undulatus species group of the large and diversified iguanid genus Sceloporus. Five species (including 15 species and subspecies) currently are recognized in the undulatus group: ScelopQrus undulatus (Latreille), S. cautus Smith, S. occidentalis Baird and Girard, S. virgatus Smith, and S. woodi Stejneger (Smith, 1939, 1946; Lowe and Norris, 1956; Maslin, 1956; Cole, 1963).1 The combined geographic ranges of these species incorporate approximately three-fourths of the continental United States south of Canada and most of the northern half of Mexico. Local populations within this area are adapted to a wide variety of habitats, including desert, grassland, woodland, chaparral, and forest. The present cytological investigation was undertaken as an attempt to improve our 1 A sixth species, Sceloporus exsul, recently was described by Dixon, Ketchersid, and Lieb (1972). Chromosomes of this species have not yet been examined. understanding of the evolution and relationships of the fence lizards. Comparisons of chromosomes from individuals representing both sexes of each species and nearly all the subspecies in the group has revealed a much greater potential for analyzing relationships between local populations than had been anticipated.

Chromosomes of Syrphidae. VI. The tribe Pipizini

The karyotypes of 24 species of the tribe Pipisini (Diptera: Syrphidae) are described and illustrated. Nearly all the species of Neocnemodon, Pipiza and Pipizella have 2n=8 chromosomes consisting of a short telocentric XY pair and three metacentric pairs increasing in relative length from long to very long. Pair II chromosomes in several Pipiza species have high metacentric to low submetacentric arm ratios. One Parapenium species is tentatively reported as having five pairs and another five or six pairs. The karyological evidence favours placing the tribe Pipizini in the subfamily Syrphinae rather than in the subfamily Milesiinae.

The Cytogenetics ofChthonerpeton Indistinctum(Amphibia: Gymnophiona)

SUMMARYThe cytogenetics of Chthonerpeton indistinctum was studied. The karyotype was composed of five pairs of metacentric chromosomes, four pairs of submetacentrics and one pair of telocentrics (diploid number 2n = 20).The meiotic behaviour revealed the existence of ring bivalents some of them with unter- minalized chiasmata at metaphase first, similar in structure to those found in Urodela and primitive Anura.Major spirals were present during meiotic prophase and metaphase suggesting that they are more related to Anura than to Urodela.The absence of microchromosomes and the low somatic number is markedly different with those presentend by the two only species of Apoda, I. glutinosus and U. narayani studied up to now. Furthermore, the fundamental number (FN) as well as the morphological and biological characteristics of the two mentioned species seem to be, in C. indistinctum less advanced from the evolutionary viewpoint.These considerations led us to conclude that the more advanced forms had undergone a chromosome reduction by structural rearrangements and microchromosome loss.Along the meiotic or mitotic cycles no morphological differentiation of chromosomes that may be interpreted as sex chromosomes could be found.