Figure 4. Methylation of the Avy Allele following Maternal Transmission.
The methylation status of each CpG dinucleotide was determined by sequencing PCR clones of bisulfite-converted DNA, as described in Figure 2 [4]. Each block of lines represents the clones derived from one bisulfite conversion of ten cells (oocytes or zygotes). The percentage of methylation in each dataset is shown (calculated from the number of methylated CpGs divided by the total CpGs sequenced, multiplied by 100). Clones were only included in the samples if they could be distinguished from others in the sample by CpG or non-CpG methylation. Any clones with higher than 5% non-CpG methylation (an indication of incomplete bisulfite conversion) were excluded from the dataset, and these clones made up less than 5% of all clones sequenced.
(A) and (D) Unfertilised oocytes from pseudoagouti or yellow Avy/a females, respectively. DNA methylation at the Avy allele does not appear to have been reset during oogenesis.
(B) Zygotes from pseudoagouti Avy/a dams mated to a/a sires.
(C) Blastocysts from pseudoagouti Avy/a dams mated to a/a sires. The Avy allele is not subject to rapid demethylation immediately postfertilisation following maternal inheritance, but is completely cleared of DNA methylation before blastocyst formation.