C W Beattie

A second-generation linkage map of the sheep genome.

A genetic map of Ovis aries (haploid n = 27) was developed with 519 markers (504 microsatellites) spanning ∼3063 cM in 26 autosomal linkage groups and 127 cM (female specific) of the X Chromosome (Chr). Genotypic data were merged from the IMF flock (Crawford et al., Genetics 140, 703, 1995) and the USDA mapping flock. Seventy-three percent (370/504) of the microsatellite markers on the map are common to the USDA-ARS MARC cattle linkage map, with 27 of the common markers derived from sheep. The number of common markers per homologous linkage group ranges from 5 to 22 and spans a total of 2866 cM (sex average) in sheep and 2817 cM in cattle. Marker order within a linkage group was consistent between the two species with limited exceptions. The reported translocation between the telomeric end of bovine Chr 9 (BTA 9) and BTA 14 to form ovine Chr 9 is represented by a 15-cM region containing 5 common markers. The significant genomic conservation of marker order will allow use of linkage maps in both species to facilitate the search for quantitative trait loci (QTLs) in cattle and sheep.

Physical assignments of 68 porcine cosmid and lambda clones containing polymorphic microsatellites

Two lambda phage and 66 cosmids containing informative porcine microsatellites were assigned to 17 of 18 porcine autosomes and the X Chromosome (Chr) by fluorescence in situ hybridization (FISH). These assignments provide additional physically anchored markers to integrate the porcine physical and genetic maps.

Microsatellite Evolution: Testing the Ascertainment Bias Hypothesis

Abstract. Previous studies suggest the median allele length of microsatellites is longest in the species from which the markers were derived, suggesting that an ascertainment bias was operating. We have examined whether the size distribution of microsatellite alleles between sheep and cattle is source dependent using a set of 472 microsatellites that can be amplified in both species. For those markers that were polymorphic in both species we report a significantly greater number of markers (P < 0.001) with longer median allele sizes in sheep, regardless of microsatellite origin. This finding suggests that any ascertainment bias operating during microsatellite selection is only a minor contributor to the variation observed.

The bovine homolog of the obese gene maps to Chromosome 4

region of bovine Chr 6 (Fig. 1). The chromosomes were classified according to ISCNDA, 1989 [6]. Previously identified homologs: The OBS gene is located on mouse Chr 6 [7] and human Chr 7q31.3 [8]. Discussion: The chromosomal location of OBS in cattle is concordant with expectations based on chromosome painting experiments [Zoo-FISH; 9, 10]. The cloning and sequencing of the mouse obesity gene and its human homolog reported by Zhang and associates [7] is of great interest to researchers working with farm animal species. The mouse and human OBS gene product, secreted by adipose tissue, may be involved in appetite control/regulation, regulation of fuel storage, and energy expenditure [7]. The role of OBS in feed intake regulation and the regulation of energy balance in cattle is yet to be determined.

Cytogenetic assignment of 53 microsatellites from the USDA-MARC porcine genetic map

This study provides 53 new fluorescent in situ hybridization cytogenetic assignments for microsatellite markers linked on the swine genetic map. Forty microsatellites are physically assigned for the first time. The chromosomal locations of eight markers were either confirmed or refined, while five loci were assigned to locations different from those given in previous reports. Markers were selected to provide physical anchors based on their presumed proximity to centromeres or telomeres and at approximately 30 cM intervals across the genetic map. The number of physical anchors for pig (SSC) chromosomes 8, 15, and 18 linkage groups was significantly improved. Centromeric regions were localized to areas less than 10 cM for SSC 1, 2, 3, 6, 7, 8, and 9. Although the recombination rate was generally higher across small biarmed chromosomes and lowest for large acrocentric chromosomes, two regions with particularly low (1q2.1→q2.9 and 13q2.3→q4.1) and three regions with extremely high (5p1.5→p1.2, 6p1.4→p1.3, and 12p1.5→p1.4) rates of recombination were detected. These assignments represent an overall 10% increase in the number of physically assigned markers in Sus scrofa and more than a 20% increase in the number of Type II loci assigned to the pig cytogenetic map.

Use of DISC-PCR and FISH to assign a linkage group to pig chromosome 10.

Although major advances (Fredholm et al. 1993; Rohrer et al. 1994; Ellegren et al. 1994) have been made in the development of low-resolution porcine genetic linkage maps, to date relatively few microsatellites (ms) have been physically localized. Moreover, linkage group orientation with respect to the centromere is often arbitrary, which precludes accurate estimates of genome coverage. In addition, several large linkage groups have not been assigned to a chromosomal position (Rohrer et al. 1994). Microsatellites cloned from small insert libraries for rapid sequencing are generally too small for conventional in situ hybridization to livestock chromosomes unless used as probes to isolate large genomic clones. We have recently developed a technique, direct in situ single copy (DISC) PCR that directly maps microsatellites (Troyer et al. 1994a, 1994b). The present study utilized DISC-PCR and fluorescent in situ hybridization (FISH) to chromosomally anchor a large, unassigned linkage group and verify a DISC-PCR assignment of an informative (polymorphic) MS cloned from a cosmid library. The MS Swl9 was localized with DISC-PCR to the short arm of Chromosome (Chr) 10 and the assignment confirmed with the FISH procedure. We also mapped an additional MS, Sw920, in the linkage group to Chr 10, which orients the linkage group. Metaphase chromosomes spreads were prepared from pokeweed mitogen-stimulated lymphocytes of male pigs (Troyer et al. 1994b). The approximate size of amplified product for Swl9 is 190 bp, and for Sw 920, 146 bp. Primers were designed with Primer 0.5 program (Whitehead Institute, Cambridge, Massachusetts). The forward sequence for Swl9 was CCAGGACACAGTGAGGGG; the reverse primer was AAGCCAGGTTGTCCCTCC. Conditions and primers for Sw920 are reported in Rohrer and associates (1994). The DISC-PCR reaction was run as previously reported (Troyer et al. 1994b). The annealing temperature for Swcl9 is 58~ for Sw920, 60~