Bisulfite Sequencing

Cytosines that remain unchanged after treatment are interpreted as methylated, while converted positions are read as thymine after amplification and sequencing. Researchers compare these base calls with the reference genome to localize methylation at individual genomic positions rather than only estimating a general methylation level.

Incomplete conversion can make an unmethylated cytosine appear unchanged, producing an apparent methylation signal that does not reflect the original DNA. Bisulfite treatment can also degrade DNA, which affects data quality and may reduce the reliability of sequence-based methylation measurements. These limitations are central when interpreting the resulting methylation map.

Single-base resolution shows exactly which cytosines carry methylation within a genomic region. This precision allows investigators to examine detailed patterns in promoters and across the genome instead of treating an entire region as uniformly modified. The resulting positional information supports closer comparisons among biological samples and helps identify localized epigenetic differences.

The workflow begins by treating DNA with sodium bisulfite, followed by amplification and sequencing of the treated material. Researchers then distinguish thymine and cytosine calls and compare the resulting sequence with a reference genome. This analysis converts the chemical differences produced during treatment into a map of methylated sites.

At promoters, the method can assess methylation patterns in regulatory regions associated with genes. Genome-wide analysis extends the same measurement across many genomic locations, allowing researchers to characterize broader epigenetic patterns. Together, these applications support studies of how methylation is distributed rather than restricting analysis to a single selected site.

Methylation maps can be compared across cell types, developmental stages, or disease-associated samples to identify changes in epigenetic state. Such comparisons help relate methylation patterns to differences in cell identity, developmental progression, or disease-linked alterations. Interpretation still requires attention to DNA degradation and incomplete conversion because both can influence the observed results.