The material continuity and individuality of the somatic chromosomes of Ambystoma tigrinum, with special reference to the nucleolus as a chromosomal component

Dearing, William H.

doi:10.1002/jmor.1050560108

Cited by 68 publications

(9 citation statements)

References 5 publications

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“…Early tetrad mapping studies located d in the distal region of an unknown chromosome (Lindsley et al 1955;Armstrong 1984) and several studies have observed an association between segregation of white and segregation of NOR variants (reviewed by Sinclair et al 1978). The NOR is located subterminally on one of the four largest chromosomes (Paramenter 1919;Dearing 1934;Haschuka and Brunst 1965;Callan 1966;Cuny and Malacinski 1985). In our study we identified a single region of the genome that was significantly associated with white.…”

Section: Segregation Of Molecular Markerssupporting

confidence: 55%

A Comprehensive Expressed Sequence Tag Linkage Map for Tiger Salamander and Mexican Axolotl: Enabling Gene Mapping and Comparative Genomics in Ambystoma

et al. 2005

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Expressed sequence tag (EST) markers were developed for Ambystoma tigrinum tigrinum (Eastern tiger salamander) and for A. mexicanum (Mexican axolotl) to generate the first comprehensive linkage map for these model amphibians. We identified 14 large linkage groups (125.5-836.7 cM) that presumably correspond to the 14 haploid chromosomes in the Ambystoma genome. The extent of genome coverage for these linkage groups is apparently high because the total map size (5251 cM) falls within the range of theoretical estimates and is consistent with independent empirical estimates. Unlike most vertebrate species, linkage map size in Ambystoma is not strongly correlated with chromosome arm number. Presumably, the large physical genome size (30 Gbp) is a major determinant of map size in Ambystoma. To demonstrate the utility of this resource, we mapped the position of two historically significant A. mexicanum mutants, white and melanoid, and also met, a quantitative trait locus (QTL) that contributes to variation in metamorphic timing. This new collection of EST-based PCR markers will better enable the Ambystoma system by facilitating development of new molecular probes, and the linkage map will allow comparative studies of this important vertebrate group. T HE tiger salamander (Ambystoma tigrinum) species complex consists of several closely related and phenotypically diverse taxa that range from central Mexico to southern Canada (Shaffer and McKnight 1996). The complex as a whole is an important, naturalistic model system because taxa are characterized by extensive interspecific and intraspecific variation for a number of ecologically important traits, including expression of metamorphic vs.

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Section: Segregation Of Molecular Markerssupporting

confidence: 55%

A Comprehensive Expressed Sequence Tag Linkage Map for Tiger Salamander and Mexican Axolotl: Enabling Gene Mapping and Comparative Genomics in Ambystoma

et al. 2005

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“…In 1954, Gall described a region on one of the lampbrush chromosomes from oocytes of Ambystoma tigrinurn, to which nucleoli were attached. The position of this region corresponded with that of a prominent subterminal constriction which is associated with the formation of nulceoli at mitotic telophase in this species (Dearing, 1934).…”

Section: The 'Lampbrush' Nucleolar Organizermentioning

confidence: 52%

The Nucleolus and Its Genes in Amphibian Oogenesis

Macgregor

1972

Biological Reviews

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Summary 1. Amphibian oocyte nucleoli may be solid and round, or they may take the form of beaded rings. Transformation of the nucleoli from the solid form to the ring form and back again may be a regular feature of oogenesis. The variation in circumference of freshly isolated unstretched ring nucleoli is continuous over a range of about fivefold. The longest rings may measure several hundred micra. All oocyte nucleoli have two structural zones, core and cortex. The core consists of finely fibrous material and is analogous to the ‘pars amorpha’ of earlier authors. The cortex has a granular fine structure and is analogous to the ‘nucleolonema’. The beads of ring nucleoli have both core and cortex components. Some solid nucleoli are multicored. 2. When all nucleoli are single cored, the number of nucleoli in an oocyte nucleus remains constant throughout the lampbrush phase of oogenesis. When nucleoli are multicored, the number of nucleoli may vary, but the number of nucleolar cores remains constant. 3. Oocyte nucleoli of between 6 and 12μ diameter have dry masses of between 50 and 200 μμg. 610% of the nucleolar dry mass is attributable to RNA. 4. Each nucleolus has a small DNA component. This component is in the form of a long circular duplex. In solid nucleoli it meanders through the substance of the nucleolar core. It forms the axis of a ring nucleolus and the structural integrity of the ring is maintained by the DNA component. 5. Both round and ring types of nucleoli from some salamanders and frogs have a membrane component attached to them. This takes the form of a membranous tube or a chain of vesicles ending near to or within a depression in the surface of the nucleolar core. Nothing is known at present of the function of the nucleolar membrane. 6. Nucleoli are sites of synthesis of ribosomal RNA. The DNA of the nucleolar core has the base sequence needed for transcription of ribosomal RNA. RNA is transcribed, complexed with protein and eventually distributed between 50S and 30S ribonucleoprotein particles. The 30S particle does not accumulate in the nucleolus. The 50S particle matures in the nucleolus and probably constitutes a substantial portion of the nucleolar cortex. 7. During the pachytene stage in ovaries of young amphibia 20–30 μμg. of extra‐chromosomal nucleolar DNA are synthesized. In early diplotene this DNA disperses into thousands of tiny granules which become distributed over the inner surface of the nuclear envelope. A nucleolus then grows in association with each granule. 8. Isolation and purification of nucleolar DNA from pachytene oocytes, and from germinal vesicles, has shown that it contains the sequences for 18 and 28S ribosomal RNA, and it represents the products of an amplification of the genes for ribosomal RNA. 9. In Xenopus the gene complex which is amplified consists of about 450 tandem repeats of a region of double stranded DNA which includes sequences complementary to 28 S and 18 S ribosomal RNA alternating with a spacer sequence. The density of the ribosomal DNA, including the sp...

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“…2, 3, 4, 6, and 7; Figs. [28][29][30][31][32][33][34][35][36][37][38]. The anaphase and the second division proceed normally.…”

Section: Torsten Wickbommentioning

confidence: 99%

Cytological Studies on Dipnoi, Urodela, Anura, and Emys

Wickbom¹

2010

Hereditas

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The material continuity and individuality of the somatic chromosomes of Ambystoma tigrinum, with special reference to the nucleolus as a chromosomal component

Cited by 68 publications

References 5 publications

A Comprehensive Expressed Sequence Tag Linkage Map for Tiger Salamander and Mexican Axolotl: Enabling Gene Mapping and Comparative Genomics in Ambystoma

A Comprehensive Expressed Sequence Tag Linkage Map for Tiger Salamander and Mexican Axolotl: Enabling Gene Mapping and Comparative Genomics in Ambystoma

The Nucleolus and Its Genes in Amphibian Oogenesis

Cytological Studies on Dipnoi, Urodela, Anura, and Emys

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