Sib pairs were selectively sampled for extreme concordance or discorda
nce for the quantitative trait Q1, a simulated phenotype (GAW10). Two
selective sampling criteria were used (SC1 and SC2), and results for t
hese were compared to linkage analyses using all pairs (ALL). In total
773 sib pairs were available, which reduced to an average of 59.7 pai
rs under SC1, and 134.1 pairs under SC2. Whole genome screens were per
formed on 10 different data replicates for each selection criterion (A
LL, SC1, and SC2). Fine screens were then performed over regions which
indicated at least suggestive linkage, and these regions were also fi
ne screened in an independent data replicate in an attempt to repeat a
ny areas found. The results for the coarse genome screens were similar
under each of the criteria, although in general lower maxima and slig
htly more erratic lods were found under the stricter selection methods
. The correct region on chromosome 5 (responsible for approximately 22
% of the variance of Q1) was detected (p < 0.0001) in 6/10 of the data
replicates using ALL, and 4/10 using SC1 and SC2. The second quantita
tive trait locus (QTL) on chromosome 8 (only 0.5% of the variance of Q
1) was detected in only a single data replicate using SC1. False posit
ive rates were similar for each criterion, whereas power decreased usi
ng selective sampling compared to ALL, although this was probably due
to an insufficient initial sample size. (C) 1997 Wiley-Liss, Inc.