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Copyright of ESPOCH Congresses: The Ecuadorian Journal of S.T.E.A.M. is the property of Knowledge E DMCC and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Eleven segregating families of chicken were constructed to map the autosomal dwarf (adw) locus in chicken. Genetic linkage of the adw locus to five different microsatellite markers on chromosome 1 was observed. The high-mobility group protein I-C (HMGI-C) gene was found to be a prime candidate for the adw locus in the chicken. Fluorescence in situ hybridization of metaphase chromosomes with the chicken HMGI-C gene as a probe, revealed that the chicken HMGI-C gene is closely linked to marker LEI146 on chromosome 1.

In a Zoo-FISH study chicken autosomal chromosome paints 1 to 9 (GGA1–GGA9) were hybridized to metaphase spreads of nine diverse birds belonging to primitive and modern orders. This comparative approach allows tracing of chromosomal rearrangements that occurred during bird evolution. Striking homologies in the chromosomes of the different species were noted, indicating a high degree of evolutionary conservation in avian karyotypes. In two species, the quail and the goose, all chicken paints specifically labeled their corresponding chromosomes. In three pheasant species as well as in the American rhea and blackbird, GGA4 hybridized to chromosome 4 and additionally to a single pair of microchromosomes. Furthermore, in the pheasants fission of the ancestral galliform chromosome 2 could be documented. Hybridization of various chicken probes to two different chromosomes or to only the short or long chromosome arm of one chromosome pair in the species representing the orders Passeriformes, Strigiformes, and Columbiformes revealed translocations and chromosome fissions during species radiation. Thus comparative analysis with chicken chromosome-specific painting probes proves to be a rapid and comprehensive approach to elucidate the chromosomal relationships of the extant birds. Copyright © 2003 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Differentiated sex chromosome pairs in diverse species display certain common characteristics, normally comprising one largely heterochromatic genetically inactive chromosome and one euchromatic genetically active chromosome (e.g. the mammalian Y and X respectively). It is widely accepted that dimorphic sex chromosomes evolved from homologous pairs of autosomes. Although the exact mechanisms through which the pair diverged are not fully understood, an initial suppression of recombination in the sex-determining region is required by all of the major theories. Here we address the question of the mechanism by which this initial suppression of recombination occurs. Our model postulates that the stochastic, de novo accumulation of heterochromatin in the sex determining region can delay pairing of the sex chromosomes in meiosis, resulting in a decrease in recombination. Data to support this model is presented from the cichlid fish, Oreochromis niloticus. Although such a decrease would in most circumstances be evolutionarily disadvantageous, if the region concerned included the major sex determining gene and other gene(s) with sex-specific functions, then this would be selectively advantageous and could trigger the process(es) which, ultimately, lead to the differentiation of the sex chromosomes. Copyright © 2002 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract Background Comparative genomics is a powerful means of establishing inter-specific relationships between gene function/location and allows insight into genomic rearrangements, conservation and evolutionary phylogeny. The availability of the complete sequence of the chicken genome has initiated the development of detailed genomic information in other birds including turkey, an agriculturally important species where mapping has hitherto focused on linkage with limited physical information. No molecular study has yet examined conservation of avian microchromosomes, nor differences in copy number variants (CNVs) between birds. Results We present a detailed comparative cytogenetic map between chicken and turkey based on reciprocal chromosome painting and mapping of 338 chicken BACs to turkey metaphases. Two inter-chromosomal changes (both involving centromeres) and three pericentric inversions have been identified between chicken and turkey; and array CGH identified 16 inter-specific CNVs. Conclusion This is the first study to combine the modalities of zoo-FISH and array CGH between different avian species. The first insight into the conservation of microchromosomes, the first comparative cytogenetic map of any bird and the first appraisal of CNVs between birds is provided. Results suggest that avian genomes have remained relatively stable during evolution compared to mammalian equivalents.

We used chromosome painting with chromosome-specific probes derived from domestic sheep and pig for a high-resolution cytogenetic comparison with the karyotype of collared peccary (Pecari tajacu sonoriensis). A reorganization of the karyotype involving at least 62-66 conserved segments were observed between the sheep and collared peccary. This is an extremely high number compared with other members of the same mammalian order (Cetartiodactyla). The comparison between pig and collared peccary, both belonging to the Suiformes, however, revealed various changes in the gross organization of both karyotypes that may have already occurred in a common ancestor of both species suggesting a monophyletic origin of Suidae/Tayassuidae. The sheep probes, however, also revealed several rearrangements between the two Suidae/Tayassuidae, indicating that these probes represent a useful tool for a more detailed analysis of the evolutionary history of Suiformes. Our sample of the collared peccary from North America (Arizona, USA) showed distinct differences to those already described from South America. The chromosome painting results defined a complex translocation that involves chromosomes including about one-quarter of the entire collared peccary karyotype. This considerable rearrangement indicates subspecies or even species status of both peccary populations, as it should present a significant barrier for their hybridization.

Heterozygous carriers of mutations in the BRCA2 gene have a high risk of developing breast and other cancers. In these individuals, BRCA2 appears to act as a tumour suppressor gene, in that loss of the wild type allele is frequently observed within tumours, leading to loss of BRCA2 function. Because BRCA2 functions in DNA repair via homologous recombination, this leads to genomic instability. However, it is unclear whether loss of the wild type allele is stochastic or if heterozygosity for BRCA2 mutation carries a phenotype that contributes to tumorigenic progression. Here we demonstrate that, in a specific vertebrate cell type, the chicken B cell line DT40, heterozygosity for a BRCA2 mutation has a distinct phenotype. This is characterized by a reduced growth rate, increased cell death, heightened sensitivity to specific DNA damaging agents and reduced RAD51 focus formation after irradiation. Thus in certain cell types, genome instability might be driven directly by heterozygosity for BRCA2 mutation.

Carriers of mutations in the BRCA2 gene have a high risk of developing breast and other cancers. The BRCA2 gene, which is located on human chromosome 13, encodes a very large protein of only poorly understood function. To define regions of sequence conservation and highlight potentially functionally important domains, we have cloned and characterized the chicken BRCA2 gene, the first non-mammalian BRCA2 gene to be described. The gene is organized similarly to the human BRCA2 gene, but is more compact and is localized to the subtelomeric region of chicken chromosome 1q, within a region that contains other genes from human chromosome 13. The chicken BRCA2 gene encodes a protein of 3399 amino acids, which is poorly conserved with mammalian BRCA2 proteins, having only 37% amino acid identity overall with human BRCA2. However, certain domains are much more highly conserved, indicating functional significance. We describe genes with some of these conserved domains in organisms as diverse as intracellular parasites, mosquitoes and plants. The evolutionarily divergent chicken BRCA2 sequence may also be useful in assigning the large number of sequence variants that have been described in the human BRCA2 gene which are of unknown significance in disease causation.

In this study we present the complete genomic structure of the bovine PLP gene and its assignment to the long arm of the X-chromosome (BTXq2.1). We determined a total of 18,767 bp of the bovine PLP gene and compared it to the human heterolog. A very high similarity was detected between the non-coding regions, interrupted primarily by several transposable elements. A deletion of 13 bp in the vicinity to the translation start signal in the promoter of the bovine PLP gene was found. Functional studies of the 3' region showed the use of several polyadenylation signals. Three main transcripts were detected in adult cattle in the range of 3200, 2400, and 1600 nucleotides using Northern blot analysis. An additional shorter transcript was detected in the cerebrum of calves.

A bovine large-insert DNA library has been constructed in a Bacterial Artificial Chromosome (BAC) vector. The source DNA was derived from lymphocytes of a Jersey male. High-molecular-weight DNA fragments were produced by treatment with EcoRI/EcoRI methylase and cloned into the EcoRI site of pBACe3.6. In total, 157,240 individual BACs have been picked into 384-well plates. Approximately 190 randomly chosen clones have been characterized by Pulsed Field Gel Electrophoresis (PFGE) and have an average insert size of 105 kb, suggesting library coverage representing 5-6 genome equivalents. The frequency of clones without inserts is 4%. The chromosomal location of 51 BACs was studied by FISH; 3 showed more than one signal, indicating a chimerism frequency of roughly 6%. Approximately 50% of the clones in the library contain Simple Repeat Sequences (microsatellites), and 4% of the clones contain centromeric repeats. Insert stability was assessed by restriction digestion of DNA prepared from 20 clones after serial culture for one and three nights. Only one clone showed any evidence of an altered restriction pattern. Clones from 360 x 384-well plates (138,240 colonies) were gridded onto high-density membranes, and PCR superpools were produced from the same set of clones. Both membranes and superpools are available from the RZPD, Berlin (http://www.rzpd.de). PCR 4-D superpools have been prepared from an additional 23,000 clones. The library has been screened for a total of 24 single-copy sequences; positive clones have been obtained in all cases.

A closed YAC contig spanning the mh locus was assembled by STS content mapping with seven microsatellite markers, eight genes or EST, and nine STS corresponding to YAC ends. The contig comprises 27 YACs, has an average depth of 4.3 YACs, and spans an estimated 1.2 Mb. A linkage map was constructed based on five of the microsatellite markers anchored to the contig and shown to span 7 cM, yielding a ratio of 160 kb/1 cM for the corresponding chromosome region. Comparative mapping data indicate that the constructed contig spans an evolutionary breakpoint connecting two chromosome segments that are syntenic but not adjacent in the human. Consolidation of human gene order by means of whole genome radiation hybrids and its comparison with the bovine order as inferred from the contig confirm conservation of gene order within segments.

Vacuolar proton-translocating ATPases (V-ATPase) are multisubunit enzyme complexes located in the membranes of eukaryotic cells regulating cytoplasmic pH. So far, nothing is known about the genomic organization and chromosomal location of the various subunit genes in higher eukaryotes. Here we describe the isolation and analysis of a cDNA coding for the 54- and 56-kDa porcine V-ATPase subunit alpha and beta isoforms. We have determined the genomic structure of the V-ATPase subunit gene spanning at least 62 kb on Chromosome (Chr) 4q14-q16. It consists of 14 exons with sizes ranging from 54 bp to 346 bp, with a non-coding first exon and an alternatively spliced seventh exon leading to two isoforms. The 5' end of the V-ATPase cDNA was isolated by RACE-PCR. The V-ATPase alpha isoform mRNA, lacking the seventh exon, has an open reading frame of 1395 nucleotides encoding a hydrophilic protein of 465 amino acids with a calculated molecular mass of 54.2 kDa and a pI of 7.8, whereas the beta isoform has a length of 1449 nucleotides encoding a protein of 483 amino acids with a calculated molecular mass of 55.8 kDa. Amino acid and DNA sequence comparison revealed that the porcine V-ATPase subunit exhibits a significant homology to the VMA13 subunit of Saccharomyces cerevisiae V-ATPase complex and V-ATPase subunit of Caenorhabditis elegans.

Despite the chicken being one of the most genetically mapped of all animals, its karyotype remains poorly defined. This is primarily due to microchromosomes that belie assignment by conventional methods. To address this problem, we have developed chromosome-specific paints using flow cytometry and microdissection. For the microchromosomes it was necessary to amplify and label DNA from single microdissected chromosomes., (Copyright 2000 S. Karger AG, Basel)