Table 3. Estimates of mean selective constraint in intron sequences.

Intronic DNA data set	Constraint
5′ bases 1-2	1.0 (0.0)
5′ bases 3-6	0.57 (0.044)
5′ bases 7-10	0.025 (0.076)
3′ bases 1-2	1.0 (0.0)
3′ bases 3-16	0.31 (0.031)
3′ bases 17-30	0.15 (0.040)
Intron 1, 5′ end	0.10 (0.017)
Intron 1, 3′ end	0.0056 (0.016)

In the analysis of intron 1, up to 6,000 bp at the 3′ or 5′ ends were analyzed. If a first intron was <12,000 bp long, the intron sequence was divided equally at the central nucleotide between data sets of 5′ and 3′ sequences. SEMs are shown in parentheses.