Table I. Percentage of XCI in cord blood, and in maternal and paternal grandmother’s blood

Locus	Cord blood	Maternal blood	Paternal grandmother blood
AR^a	(ac) 96% mat	(bd) 97% allele a	(bc) 91% allele b
FMR1^a	(ab) 99% mat	(ac) 100% allele c	(bb) homozygous
DXS6673E^b	(ab) 86% mat	(aa) homozygous	(bb) homozygous

a, b, c and d in parentheses are different alleles at a particular gene locus.

Percentages shown are, for most of the samples, the average of two independent assays carried out using two different digestions.

Based on this genotype, preferentially inactivated alleles are designated as ‘mat’ for maternal. Preferentially inactive maternal alleles are designated using the corresponding letters of the alphabet.

^aAR and FMR1 were tested using the same two digests.

^bXCI values calculated for DXS6673E may be inaccurate due to allele overlap at the level of stutter bands.