Objective—To estimate the number of dogs required
to find linkage to heritable traits of hip dysplasia in
dogs from an experimental pedigree.
Animals—147 Labrador Retrievers, Greyhounds, and
their crossbreed offspring.
Procedure—Labrador Retrievers with hip dysplasia
were crossed with unaffected Greyhounds. Age at
detection of femoral capital ossification, distraction
index (DI), hip joint dorsolateral subluxation (DLS) score,
and hip joint osteoarthritis (OA) were recorded. Power
to find linkage of a single marker to a quantitative trait
locus (QTL) controlling 100% of the variation in a dysplastic
trait in the backcross dogs was determined.
Results—For the DI at the observed effect size,
recombination fraction of 0.05, and heterozygosity of
0.75, 35 dogs in the backcross of the F1 to the
Greyhound generation would yield linkage at a power
of 0.8. For the DLS score, 35 dogs in the backcross to
the Labrador Retriever generation would be required
for linkage at the same power. For OSS, 45 dogs in
the backcross to the founding Labrador Retrievers
would yield linkage at the same power. Fewer dogs
were projected to be necessary to find linkage to hip
OA. Testing for linkage to the DLS at 4 loci simultaneously,
each controlling 25% of the phenotypic variation,
yielded an overall power of 0.7.
Conclusions and Clinical Significance—Based on
this conservative single-marker estimate, this pedigree
has the requisite power to find microsatellites
linked to susceptibility loci for hip dysplasia and hip
OA by breeding a reasonable number of backcross
dogs. (Am J Vet Res 2003;222:418–424)