Animal models for discovery and assessment of genetic determinants of osteoporosis

Excerpt

Quantitative trait locus (QTL) mapping is the process of identifying, by both chromosomal position and effect, the major genetic contributors to natural-population (or interstrain) variation in the trait of inquiry. The polymorphic alleles, or variants, thus observed are distinct from variants turned up through mutagenesis screens in that each QTL allele exists in nature at a far higher level than could be maintained by the rate of new mutation. This tells us that none of the alleles confers a selective disadvantage, since even a 1% decrease in fitness is sufficient to eliminate that allele within a relatively short evolutionary time span. Thus, each QTL allele is equally normal, or "wild-type." …