Differences between the radiation hydrid and genetic linkage maps of bovine Chromosome 5 resolved with a quasi-phylogenetic method of analysis

Two major differences were detected in gene order between the radiation hybrid map and the genetic linkage map of bovine Chromosome (Chr) 5, and these were resolved by analyzing the raw radiation hybrid data by a quasi-phylogenetic method. Seventeen loci were typed on the new cattle whole genome radiation hybrid panel. Most of these loci are framework loci and include AGLA293, BM315, BM6026, BP1, BZRP, CD9, CSSM22, CSSM34, CYP2D@, ETH2, ETH10, ETH152, IGF1, LALBA, SLC2A3, SYT1, and TPI1. BP1 was found to be closer to the centromere than either BM6026 or SYT1 with two standard computer software packages for analyzing radiation hybrid panel data. This is inconsistent with any of the genetic linkage maps as well as their consensus. CYP2D@ was placed between ETH2 and BZRP, and this is also inconsistent with the genetic linkage maps, since CYP2D@ should be the most telomeric of the loci tested in this study. Resolution was reached by analyzing the raw radiation hybrid data for clones that bind some but not all of the loci, and the binding pattern was more consistent with the linkage maps and less consistent with the software-generated radiation hybrid map. The comparative mapping data confirm the relative inversion of gene order of SYT1 compared with humans and mice. A non-polymorphic fragment for CD9 indicates the conservation of gene order for three loci located on human Chr 12p. The genes of bovine Chr 5 conserved on human Chr 12p are located separately from the genes conserved on human Chr 12q. It is recommended that the raw data for radiation hybrid maps be made publicly available so that conflicts in gene order can be evaluated explicity. Received: 19 February 1999 / Accepted: 3 January 2000     

Construction of a bovine Chromosome 19 linkage map with an interspecies hybrid backcross

Interspecific hybrid backcross animals from a Bos taurus×Bos gaurus F₁ female were used to construct a linkage map of bovine Chromosome (Chr) 19. This map includes eight previously unmapped type I anchor loci, CHRNB1, CRYB1, GH1, MYL4, NF1, P4HB, THRA1, TP53, and five microsatellite markers, HEL10, BP20, MAP2C, ETH3, BMC1013, from existing linkage maps. The linkage relationship was determined to be centromere–HEL10–18.8cM–NF1–4.0cM–CRYB1–11.2cM–(BP20, CHRNB1, TP53)–4.0cM–(MAP2C, GH1, MYL4, THRA1)–14.4cM–P4HB–11.2cM–ETH3–4.0cM–BMC1013. It was previously revealed that bovine Chr 19 contains the largest known conserved autosomal synteny among human, bovine, and mouse. This study has shown that gene orders within this segment are not conserved among the three species. We propose structural changes in an ancestral mammalian chromosome to account for these differences. This is the first interspecific hybrid backcross used in bovine linkage studies, and it has proven to be an effective tool for incorporating bovine type I loci into the linkage map even with the small sample size presently available. This resource will facilitate the generation of comparative linkage maps that address gene order and effectively predict the locations of unmapped loci across species. Received: 11 June 1996 / Accepted: 19 November 1996     

An expanded comparative map of bovine chromosome 27 targeting dairy form QTL regions

At present, the density of genes on the bovine maps is extremely limited and current resolution of the human-bovine comparative map is insufficient for selection of candidate genes controlling many economic traits of interest in dairy cattle. This study describes the chromosomal mapping of 10 selected gene-associated markers to bovine linkage and radiation hybrid maps to improve the breakpoint resolution in the human-bovine comparative map near two previously identified quantitative trait loci for the linear type trait, dairy form. Two regions of conserved synteny not previously described are reported between the telomeric region of bovine chromosome 27 (BTA27) and human chromosome 3 (HSA3) p24 region and between the HSA4q34.1 region and BTA8. These data increase the number of genes positioned on the bovine gene maps, refine the human-bovine comparative map, and should improve the efficiency of candidate gene selection for the dairy form trait in cattle.     

EST derived SSR markers for comparative mapping in wheat and rice

Structural and functional relationships between the genomes of hexaploid wheat (Triticum aestivum L.) (2n=6x=42) and rice (Oryza sativa L.) (2n=2x=24) were evaluated using linkage maps supplemented with simple sequence repeat (SSR) loci obtained from publicly available expressed sequence tags (ESTs). EST-SSR markers were developed using two main strategies to design primers for each gene: (1) primer design for multiple species based on supercluster analysis, and (2) species-specific primer design. Amplification was more consistent using the species-specific primer design for each gene. Forty-four percent of the primers designed specifically for wheat sequences were successful in amplifying DNA from both species. Existing genetic linkage maps were enhanced for the wheat and rice genomes using orthologous loci amplified with 58 EST-SSR markers obtained from both wheat and rice ESTs. The PCR-based anchor loci identified by these EST-SSR markers support previous patterns of conservation between wheat and rice genomes; however, there was a high frequency of interrupted colinearity. In addition, multiple loci amplified by these primers made the comparative analysis more difficult. Enhanced comparative maps of wheat and rice provide a useful tool for interpreting and transferring molecular, genetic, and breeding information between these two important species. These EST-SSR markers are particularly useful for constructing comparative framework maps for different species, because they amplify closely related genes to provide anchor points across species.Communicated by R. Hagemann     

A radiation hybrid map of bovine chromosome one

Radiation hybrid (RH) mapping has proven to be an extremely powerful approach to constructing high density maps of human chromosomes and is experiencing increased use in other animals, including cattle. A 5000 rad bovine whole-genome radiation hybrid panel was recently constructed in order to integrate existing cattle linkage maps with evolutionarily conserved genes and provide high resolution comparative maps relative to humans and mice. We utilized this panel to construct a 19 marker framework map of bovine chromosome 1 (BTA1), which included 8 Type I loci and 11 Type II loci ordered with at least 1000:1 odds. A 35 marker comprehensive map including 15 Type I loci and 20 Type II loci was also produced. Of the 15 Type I loci ordered on the comprehensive map, three are ordered on HSA3 and five are ordered in three blocks on HSA21 on the human cytogenetic maps.     

A second-generation genetic linkage map of the baboon (Papio hamadryas) genome

Construction of genetic linkage maps for nonhuman primate species provides information and tools that are useful for comparative analysis of chromosome structure and evolution and facilitates comparative analysis of meiotic recombination mechanisms. Most importantly, nonhuman primate genome linkage maps provide the means to conduct whole genome linkage screens for localization and identification of quantitative trait loci that influence phenotypic variation in primate models of common complex human diseases such as atherosclerosis, hypertension, and diabetes. In this study we improved a previously published baboon whole genome linkage map by adding more loci. New loci were added in chromosomal regions that did not have sufficient marker density in the initial map. Relatively low heterozygosity loci from the original map were replaced with higher heterozygosity loci. We report in detail on baboon chromosomes 5, 12, and 18 for which the linkage maps are now substantially improved due to addition of new informative markers.     

Consensus and comprehensive linkage maps of bovine chromosome 7

The objective of this project was to integrate the currently available linkage maps for bovine chromosome 7 (BTA7) by combining data sets from eight research groups. A total of 54 unique markers were typed in eight pedigrees. Multilocus linkage analysis with CRI-MAP produced a bovine chromosome 7 consensus framework map of 27 loci ordered with odds greater than 1000:1. Furthermore, we present a bovine chromosome 7 comprehensive map integrating 54 loci. The locus order is in general agreement with the recently published linkage maps except for one discrepancy. The order of loci BM9289, BMS713, and ILSTS001 was reversed in the consensus framework map relative to the published USDA-MARC bovine chromosome 7 linkage map.     

Extensive genomic conservation of cattle microsatellite heterozygosity in sheep

We report the evaluation of 1036 bovine microsatellite primer pairs for their suitability as linkage markers in sheep. Approximately 58% (605/1036) of bovine primer pairs amplified a locus in sheep. Sixty-seven per cent (409/605) of amplified loci were detected as polymorphic. Marker heterozygosity, allele number and range of allele sizes were significantly lower in sheep than cattle sampled in this study. However, median fragment size was similar. These data suggest that high-resolution comparative linkage maps between closely related species can be constructed relatively efficiently.     

Comparative mapping of the ovine clpg locus

We used a comparative mapping approach to identify segments of conserved synteny between human Chromosome 14 (HSA14), bovine Chromosome 21 (BTA21), and the portion of ovine Chromosome 18 (OAR18) that contains the clpg locus. A bovine radiation hybrid map of the region was constructed with available Type II genetic markers and seven candidate genes to establish the comparative interval between BTA21 and HSA14. We developed polymorphic microsatellite and SNP markers associated with five candidate genes and placed them on the ovine and/or bovine genetic maps by multipoint linkage analysis. Three additional genes were mapped by virtue of their physical linkage to genetically mapped makers. Development of integrated linkage and physical maps facilitates the selection of positional candidate genes from the gene rich human map. The physically linked candidate genes PREF-1 and MEG3 map to the interval containing the clpg locus. Comparative biology suggests imprinting of MEG3 and/or the influences of PREF-1 on cellular differentiation, should be examined for their role in the parent-of-origin dependent influence of mutant clpg alleles on sheep muscle characteristics. Received: 3 February 2000 / Accepted: 19 April 2000     

A human genome map of comparative anchor tagged sequences.

Effective comparative mapping inference utilizing developing gene maps of animal species requires the inclusion of anchored reference loci that are homologous to genes mapped in the more "gene-dense" mouse and human maps. Nominated anchor loci, termed comparative anchor tagged sequences (CATS), have been ordered in the mouse linkage map, but due to the dearth of common polymorphisms among human coding genes have not been well represented in human linkage maps. We present here an ordered framework map of 314 comparative anchor markers in humans based on mapping analysis in the Genebridge 4 panel of radiation hybrid cell lines, plus empirically optimized CATS PCR primers which detect these markers. The ordering of these homologous gene markers in human and mouse maps provides a framework for comparative gene mapping of representative mammalian species.     

Extended physical maps and a consensus physical map of the homoeologous group-6 chromosomes of wheat (Triticum aestivum L. em Thell.)

Extended physical maps of chromosomes 6A, 6B and 6D of common wheat (Triticum aestivum L. em Thell., 2n=6x=42, AABBDD) were constructed with 107 DNA clones and 45 homoeologous group-6 deletion lines. Two-hundred and ten RFLP loci were mapped, including three orthologous loci with each of 34 clones, two orthologous loci with each of 31 clones, one locus with 40 clones, two paralogous loci with one clone, and four loci, including three orthologs and one paralog, with one clone. Fifty five, 74 and 81 loci were mapped in 6A, 6B and 6D, respectively. The linear orders of the mapped orthologous loci in 6A, 6B and 6D appear to be identical and 65 loci were placed on a group-6 consensus physical map. Comparison of the consensus physical map with eight linkage maps of homoeologous group-6 chromosomes from six Triticeaespecies disclosed that the linear orders of the loci on the maps are largely, if not entirely, conserved. The relative distributions of loci on the physical and linkage maps differ markedly, however. On most of the linkage maps, the loci are either distributed relatively evenly or clustered around the centromere. In contrast, approximately 90% of the loci on the three physical maps are located either in the distal one-half or the distal two-thirds of the six chromosome arms and most of the loci are clustered in two or three segments in each chromosome. Received: 19 April 1999 / Accepted: 28 July 1999     

Genetic Mapping of Laminaria japonica and L. Iongissima Using Amplified Fragment Length Polymorphism Markers in a ＂Two-Way Pseudo- Testcross＂ Strategy

With a ＂two-way pseudo-testcross＂ mapping strategy, we applied the amplified fragment length polymorphism （AFLP） markers to construct two moderate density genetic linkage maps for Laminaria. The linkage maps were generated from the 60 progenies of the F1 cross family （Laminaria iongissima Aresch. × L. Japonica Miyabe） with twenty pairs of primer combinations. Of the 333 polymorphic loci scored in 60 progenies, 173 segregated in a 1：1 ratio, corresponding to DNA polymorphisms heterozygous in a single parent, and the other 58 loci existing in both parents followed a 3：1 Mendelian segregation ratio. Among the loci with 1：1 segregating ratios, 79 loci were ordered in 14 linkage groups （648.6 cM） of the paternal map, and 72 loci were ordered in 14 linkage groups （601.9 cM） of the maternal map. The average density of loci was approximately 1 per 8 cM. To Investigate the homologies between two parental maps, we used 58 loci segregated 3：1 for further analysis, and deduced one homologous linkage group. The linkage data developed in these maps will be useful for detecting loci-controlling commercially important traits for Laminaria.     

Comparative mapping of bovine chromosome 13 by fluorescence in situ hybridization

We present chromosomal fluorescence in situ hybridization (FISH) results that both extend the HSA20/BTA13 comparative map as well as cytogenetically anchor two microsatellite markers. A bovine bacterial artificial chromosome (BAC) library was screened for conserved genes (type I loci) previously assigned to HSA10 or HSA20 and BTA13, and for microsatellites selected from two published BTA13 linkage maps. Clones from six out of nine comparative loci and both microsatellites were found represented in the BAC library. These BAC clones were used as probes in single colour FISH to determine the chromosome band position of each locus. As predicted by the human/bovine comparative map, all type I loci mapped to BTA13. Because single colour FISH analysis revealed that the loci were clustered within the distal half of BTA13, dual colour FISH was used to confirm the locus order. Established order was centromere- PRNP-(SODIL/AVP/OXT)-(BL42/GNAS1)-HCK-CSSM30 . The findings confirm the presence of a conserved HSA20 homologous synteny group on BTA13 distal of a HSA10 homologous segment.     

A genetic map of DNA loci on bovine chromosome 1

We constructed a genetic map of most of the length of bovine chromosome 1 using the CSIRO and the Texas A&M University cattle reference families. Twelve loci are in a single linkage group, 9 of which are highly polymorphic loci. Four loci are of known biochemical function, α-1 crystallin (CRYA1), γ-s crystallin (CRYGS), superoxide dismutase 1 (SOD1), and uridine monophosphate synthase (LIMPS), and these have also been previously mapped in humans. The loci CRYA 1, CSRD 1613, GMBT 7, RM 95, SOD I, and LIMPS had been previously assigned to bovine syntenic group U10, while CSRD 1613 and LIMPS had also been assigned to chromosome 1 by in situ hybridization. All of the loci show statistically significant linkage to at least one other locus. The conserved loci indicate that there have been major rearrangements during the evolution of bovine chromosome 1 compared to other mammalian chromosomes. The estimate of the total length of the linkage group is 168 cM, which accords well with the predicted length based on chiasmata frequencies for the bovine genome and the relative size of chromosome 1 in the bovine genome.     

A genetic linkage map for coho salmon (Oncorhynchus kisutch)

Construction of genetic linkage maps is an important first step for a variety of genomic applications, such as selective breeding in aquaculture, comparative studies of chromosomal evolution and identification of loci that have played key roles in the evolution of a species. Here we present a sex-specific linkage map for coho salmon. The map was constructed using 148 AFLP markers, 133 microsatellite loci and the phenotypic locus SEX . Twenty-four linkage groups spanning 287.4 cM were mapped in males, and 33 linkage groups spanning 429.7 cM were mapped in females. Several male linkage groups corresponded to two female linkage groups. The combination of linkage groups across both sexes appeared to characterize regions of 26 chromosomes. Two homeologous chromosomes were identified based on information from duplicated loci. Homologies between the coho and rainbow trout maps were examined. Eighty-six loci were found to form common linkage relationships between the two maps; these relationships provided evidence for whole-arm fissions, fusions and conservation of chromosomal regions in the evolution of these two species.     

A medium-density genetic linkage map of the bovine genome

A cattle genetic linkage map was constructed which covers more than 95 percent of the bovine genome at medium density. Seven hundred and forty six DNA polymorphisms were genotyped in cattle families which comprise 347 individuals in full sibling pedigrees. Seven hundred and three of the loci are linked to at least one other locus. All linkage groups are assigned to chromosomes, and all are orientated with regards to the centromere. There is little overall difference in the lengths of the bull and cow linkage maps although there are individual differences between maps of chromosomes. One hundred and sixty polymorphisms are in or near genes, and the resultant genome-wide comparative analyses indicate that while there is greater conservation of synteny between cattle and humans compared with mice, the conservation of gene order between cattle and humans is much less than would be expected from the conservation of synteny. This map provides a basis for high-resolution mapping of the bovine genome with physical resources such as Yeast and Bacterial Artificial Chromosomes as well as providing the underpinning for the interpolation of information from the Human Genome Project. Received: 15 August 1996 / Accepted: 15 September 1996     

Comparative mapping of bovine chromosome 27 with human chromosome 8 near a dairy form QTL in cattle

In the absence of a complete and annotated bovine genome sequence, detailed human-bovine comparative maps are one of the most effective tools for identification of positional candidate genes contributing to quantitative trait loci (QTL) in cattle. In the present study, eight genes from human chromosome 8 were selected for mapping in cattle to improve breakpoint resolution and confirm gene order on the comparative map near the 40 cM region of the BTA27 linkage map where a QTL affecting dairy form had previously been identified. The resulting map identified ADRB3 as a positional candidate gene for the QTL contributing to the dairy form trait based on its estimated position between 40 and 45 cM on the linkage map. It is also a functional candidate gene due to its role in fat metabolism, and polymorphisms in the ADRB3 gene associated with obesity and metabolic disease in humans, as well as, carcass fat in sheep. Further studies are underway to investigate the existence of polymorphisms in the bovine ADRB3 gene and their association with traits related to fat deposition in cattle.     

Comparative mapping between<Emphasis Type="Italic"> Quercus</Emphasis> and<Emphasis Type="Italic"> Castanea</Emphasis> using simple-sequence repeats (SSRs)

Simple sequence repeat (SSR) markers from Quercus and Castanea were used for comparative mapping between Quercus robur (L.) and Castanea sativa (Mill.). We tested the transferability of SSRs developed in Quercus to Castanea and vice-versa. In total, 47% (25) of the Quercus SSRs and 63% (19) of the Castanea SSRs showed a strong amplification product in the non-source species. From these 44 putative comparative anchor tags, 19 (15 from Quercus and 4 from Castanea) were integrated in two previously established genetic linkage maps for the two genera. SSR loci were sequenced to confirm the orthology of the markers. The combined information from both genetic mapping and sequence analysis were used to determine the homeology between seven linkage groups, aligned on the basis of pairs or triplets of common markers, while two additional groups were matched using a single microsatellite marker. Orthologous loci identified between Q. robur and C. sativa will be useful as anchor loci for comparative mapping studies within the Fagaceae family.Communicated by D.B. NealeThis paper is dedicated to the memory of Paulo Costa