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H A McQueen

Publications and source records attributed to H A McQueen.

9 recordsLinked to original sources
PubMed2001

Dosage compensation in birds.

The Z and W sex chromosomes of birds have evolved independently from the mammalian X and Y chromosomes [1]. Unlike mammals, female birds are heterogametic (ZW), while males are homogametic (ZZ). Therefore male birds, like female mammals, carry a double dose of sex-linked genes relative to the other sex. Other animals with nonhomologous sex chromosomes possess "dosage compensation" systems to equalize the expression of sex-linked genes. Dosage compensation occurs in animals as diverse as mammals, insects, and nematodes, although the mechanisms involved differ profoundly [2]. In birds, however, it is widely accepted that dosage compensation does not occur [3-5], and the differential expression of Z-linked genes has been suggested to underlie the avian sex-determination mechanism [6]. Here we show equivalent expression of at least six of nine Z chromosome genes in male and female chick embryos by using real-time quantitative PCR [7]. Only the Z-linked ScII gene, whose ortholog in Caenorhabditis elegans plays a crucial role in dosage compensation [8], escapes compensation by this assay. Our results imply that the majority of Z-linked genes in the chicken are dosage compensated.

Aconitate Hydratase↗
PubMed1999

Sequence scanning chicken cosmids: a methodology for genome screening.

The chicken genome is relatively poorly studied at the molecular level. The karyotype 2n=78 is divided into three main chromosomal sub-groups: the macrochromosomes (six pairs), the intermediate microchromosomes (four pairs) and the microchromosomes (29 pairs). Whilst the microchromosome group comprise only 25% of the DNA, increasing evidence is proving that this is disproportionate to their gene content. This paper demonstrates the utility of cosmid sequence scanning as a potential method for analysing the chicken genome, providing an economical method for the production of a molecular map. The GC content, gene density and repeat distribution are analysed relative to chromosomal origin. Results indicate that gene density is higher on the microchromosomes. During the scanning process an example of conserved linkage between chicken and human (12q34.2) has been demonstrated.

Animals↗
PubMed1998

Chicken microchromosomes are hyperacetylated, early replicating, and gene rich.

The chicken karyotype consists of 39 chromosomes of which 33 are classed as microchromosomes (MICs). MICs contain about one third of genomic DNA. The majority of mapped chicken genes are assigned to macrochromosomes (MACs), but a recent study indicated that CpG islands (CGIs), which are associated with most vertebrate genes, map predominantly to MICs. The present work establishes that chicken genes are concentrated on MICs by several criteria. Acetylated (lysine 5) histone H4, which is strongly correlated with the presence of genes, is highly enriched on MICs by immunocytochemistry. In addition, detailed analysis of chicken cosmids shows that CGI-like fragments are approximately six times denser on MICs than on MACs. Published mapping of randomly chosen genes by fluorescent in situ hybridization (FISH) also shows a significant excess of microchromosomal assignments. Finally, the finding that MICs replicate during the first half of S phase is also compatible with the suggestion that MICs represent gene-rich DNA. We use the cosmid data to predict that approximately 75% of chicken genes are located on microchromosomes. [The sequence data described in this paper have been submitted to the GenBank data library under accession nos. AJ001643 and AJ001644.]

Acetylation↗
PubMed1997

CpG islands of the pig.

We describe an analysis of the CpG islands (CGIs) of the pig. We have used both database survey and a porcine genomic library that is enriched for CGIs. Approximately half of 41 pig genomic database sequences had CGIs with an average G + C content of 65.3%, an average CpG observed/expected frequency of 0.85, and an average size of 978 bp. Of 27 CGI library clones, 16 were nonrepetitive, nonribosomal DNA and CGI-like. CGI library clones had similar average values for G + C and CpG frequency to CGIs of database genes, and an average size of 670 bp, as MseI cuts within some islands. Library clones were also shown to be low copy number and unmethylated in genomic DNA. The presence in the library of seven previously known CGI sequences was confirmed as was the absence of one nonisland sequence. The CGI library exhibits an R-band pattern for many chromosomes in FISH analysis. The pig chromosome arms that show the most dense CGI population are homologous to segments of human chromosomes that are known to be gene rich.

Animals↗
PubMed1996

CpG islands of chicken are concentrated on microchromosomes.

The chicken karyotype comprises 39 chromosome pairs of which at least 29 are 'microchromosomes'. Microchromosomes account for about 25% of the genomic DNA, but they are cytologically indistinguishable from one another (1). Due to technical limitations there is a strong bias of mapped genes within the chicken genome database ChickGBASE (2) towards macrochromosomes 1-6 and Z, with specific assignments to only one microchromosome (3,4). Several genes have, however, been assigned to the microchromosome group as a whole (3,5-9), demonstrating that these tiny chromosomes do not represent genetically inert DNA. To determine the overall chromosomal distribution of genes, as well as to provide a mapping resource, we prepared a CpG island library from chicken using differential binding to a methyl-CpG chicken using differential binding to a methyl-CpG binding column before and after de novo methylation (10). Surprisingly, we found that chicken CpG islands are highly concentrated on the microchromosomes, whereas macrochromosomes 1-6 are comparatively gene-poor by this assay. Our results raise the possibility that gene density on chicken microchromosomes approaches the maximum value known for vertebrates.

Animals↗
PubMed1995

The PiGMaP consortium linkage map of the pig (Sus scrofa).

A linkage map of the porcine genome has been developed by segregation analysis of 239 genetic markers. Eighty-one of these markers correspond to known genes. Linkage groups have been assigned to all 18 autosomes plus the X Chromosome (Chr). As 69 of the markers on the linkage map have also been mapped physically (by others), there is significant integration of linkage and physical map data. Six informative markers failed to show linkage to these maps. As in other species, the genetic map of the heterogametic sex (male) was significantly shorter (approximately 16.5 Morgans) than the genetic map of the homogametic sex (female) (approximately 21.5 Morgans). The sex-averaged genetic map of the pig was estimated to be approximately 18 Morgans in length. Mapping information for 61 Type I loci (genes) enhances the contribution of the pig gene map to comparative gene mapping. Because the linkage map incorporates both highly polymorphic Type II loci, predominantly microsatellites, and Type I loci, it will be useful both for large experiments to map quantitative trait loci and for the subsequent isolation of trait genes following a comparative and candidate gene approach.

Animals↗
PubMedDate not supplied

A linkage map of pig chromosome 10.

Despite the large number of mapped markers along the pig genome, many chromosomes remain poorly covered. One reason for this problem is the lack of shared markers between separate mapping projects. We describe localized map integration by mapping selected markers from the United States Department of Agriculture map onto the European consortium map. Such integration of physical and genetic mapping information has enabled us to assign and orient a linkage map that extends over most of pig chromosome 10.

Animals↗