Table 1. Estimates of methylation fidelities in CpG islands of FMR1 in normal female lymphocytes.

CpG Island	No. informative dyads (sequences)	M→M Em mean (min, max; no. dyads)	U→U Eu mean (min, max; no. dyads)	U→M Ed mean (min, max; no. dyads)
Hypermethylated FMR1 (inactive X)	110 (5)	0.96 (0.95—0.98; 93)	0.83 (0.77—0.89; 24)	0.17 (0.11—0.23; 24)
Hypomethylated FMR1 (active X)	625 (29)	0 (0—0; 3)	>0.99 (0.995—1.0; 625)	<0.01 (0.00—0.005; 625)

Estimated methylation fidelities for parent-strand methyl-cytosine giving rise to methyl-cytosine in the daughter strand [E_m = P (M→M)], parent-strand unmethylated cytosine giving rise to unmethylated cytosine in the daughter strand [E_u = P(U→U)], and parent-strand unmethylated cytosine giving rise to methyl-cytosine in the daughter strand, i.e., de novo methylation [E_d = P(U → M) = 1—P(U→U)]. The number of informative CpG dyads, the number of allelic sequences from which they are derived, the means and ranges of estimates, and the number of informative dyads critical for each estimate are given. For the hypomethylated alleles, the expected number of nonconverted CpG cytosines (five) resulting from the frequency of incomplete bisulfite conversion (0.004), was substracted from the observed number (eight) to provide our estimates for this class of alleles.