Fine-mapping and construction of a bovine contig spanning the ovine
Tracy L. Shay,
Jonathan E. Beever,
James E. Womack,
Noelle E. Cockett
Department of Animal, Dairy and Veterinary Sciences, Utah State University, Logan, Utah 84322-4700, USA
Department of Genetics, Faculty of Veterinary Medicine, University of Lie`ge (B43), 20 Bd de Colonster, 4000-Lie`ge, Belgium
Department of Animal Science, University of Illinois, Urbana, Illinois 61801, USA
Department of Veterinary Pathobiology, Texas A&M University, College Station, Texas 77483, USA
Received: 31 May 2000 / Accepted: 21 September 2000
Abstract. The callipyge (CLPG) gene was fine-mapped by link-
age analysis to a 4.6-cM chromosome interval on distal ovine
OAR18q, flanked by microsatellite markers IDVGA30 and OY3.
The OAR18q linkage map and human HSA14q transcript map
were aligned by genotyping two bovine-hamster whole-genome
radiation hybrid panels with the microsatellite markers, as well as
with sequences corresponding to HSA14q genes. Using Type I loci
mapping to the IDVGA30–OY3 interval as anchor points, we have
constructed a 1.4-Mb bovine BAC contig containing the
IDVGA30–OY3 interval. We demonstrate that the IDVGA30–
OY3 interval spans approximately 770 kb and contains at least four
genes: YY1, WARS, DLK1, and GTL2.
In 1983, a male lamb exhibiting a noticeable hyperdevelopment of
the hind quarters was born in a commercial Dorset flock in Okla-
homa. This ram, called Solid Gold, produced several offspring
characterized by the same unusual phenotype, strongly suggesting
a heritable mutation. This phenotype, referred to as callipyge [<Gk
calli- beautiful + -pyge buttocks] (Cockett et al. 1994), results from
an increase in muscle mass that develops at approximately three
weeks of age, primarily affects skeletal muscle of the pelvic limb
and torso, and is accompanied by a decrease in all measures of
fatness (Jackson et al. 1997a, 1997b, 1997c; Freking et al. 1998c).
Callipyge animals are characterized by an improved feed effi-
ciency and dressing percentage, although meat quality seems ad-
versely affected (Koohmaraie et al. 1995; Freking et al. 1998b).
Histological examination of callipyge muscle revealed an increase
in proportion and diameter of fast twitch fibers (Koohmaraie et al.
1995; Carpenter et al. 1996).
The callipyge phenotype was shown by linkage analysis to be
under the control of a single locus (CLPG) that maps to the telo-
meric end of ovine Chr 18 (Cockett et al. 1994). Marker-assisted
segregation analysis revealed that the callipyge phenotype is sub-
ject to a novel mode of inheritance with a parent-of-origin effect
referred to as polar overdominance: only heterozygous individuals
(CLPG/+) having inherited the CLPG mutation from their sire
express the muscular hypertrophy (Cockett et al. 1996). The chro-
mosomal localization of the CLPG locus was subsequently refined
and the polar overdominance model confirmed by others (Freking
et al. 1998a).
The nature of the CLPG mutation and the molecular mecha-
nisms underlying polar overdominance, however, remain un-
known. As part of an effort towards positional cloning of the
CLPG gene, we have fine-mapped the CLPG locus to a 4.6-cM
marker bracket and constructed a contig spanning this interval by
using bovine YAC and BAC clones.
Materials and methods
Animal samples used for map construction and lo-
calization of the CLPG locus were part of a complex, multigenerational
pedigree comprising a total of 947 normal and 501 callipyge individuals.
Animals were reared either at Utah State University or Texas Tech Uni-
versity. Phenotypic classification was based on visual examination by ex-
perienced observers. All callipyge animals were descendants of Solid Gold.
Microsatellite genotyping was performed by using
previously described standard procedures (Georges et al. 1995). Primer
pairs used for PCR amplification of the microsatellite markers are reported
in Table 1. Minisatellite genotyping was done as previously described
(Georges et al. 1991).
The linkage information used for map construction
was extracted separately for the rams and ewes by splitting the pedigree
into a series of paternal and maternal half-sib pedigrees. This yielded 56
paternal half-sib pedigrees with an average of 13.2 offspring (range: 2–83)
and 186 maternal half-sib pedigrees with an average of 2.6 offspring
(range: 2–5). To avoid redundant information, dams of full-sibs were con-
sidered independent when extracting information from the rams and vice
versa. Marker maps were constructed by using the BUILD option of the
CRIMAP package (Lander and Green 1987). Potential double recombi-
nants were identified by using the CHROMPIC option, and their marker
genotypes were reanalyzed. The statistical significance of the difference
between male and female recombination rates was estimated from:
) corresponds to the likelihood of the data under a
model with male and female sex-specific recombination rates, while
) corresponds to the likelihood of the data assuming a unique
recombination rate identical in both sexes.
Fine-mapping of the CLPG locus.
Assuming inheritance of the calli-
pyge phenotype according to the polar overdominance model (Cockett et
al. 1996), the following chromosomes provide unambiguous information
about the location of the CLPG locus: (i) paternal chromosomes from
offspring of ( (CLPG/+) × & (+/+) matings; (ii) paternal chromosomes
from offspring of ( (CLPG/+) × & (CLPG/+) matings having inherited a
non-recombinant “+” chromosome from their dam; and (iii) maternal chro-
mosomes from offspring of ( (CLPG/+) × & (CLPG/+) matings having
Both authors contributed equally to this work.
Correspondence to: N.E. Cockett; E-mail: firstname.lastname@example.org
Mammalian Genome 12, 141–149 (2001).
© Springer-Verlag New York Inc. 2001