Bisulphite Conversion
Definition
A chemical treatment that deaminates unmethylated cytosines to uracil, converting them to thymine upon PCR amplification; methylated cytosines are protected. Allows methylation to be read as a sequence-level difference. Performed using the EZ DNA Methylation Kit or equivalent.
- Chemical effect
- Deaminates unmethylated cytosine to uracil
- After PCR
- Uracil reads as thymine; methylated cytosine stays cytosine
- Common kit
- EZ DNA Methylation Kit or equivalent
- Field
- Forensic DNA methylation phenotyping
Common questions
Why is bisulphite conversion needed to study DNA methylation forensically?+
Methylation is a chemical modification, not a change in the base sequence itself, so standard sequencing cannot see it directly. Bisulphite conversion turns the methylation state into a sequence difference (cytosine versus thymine) that ordinary sequencing or PCR-based assays can then detect and quantify.
What forensic applications rely on bisulphite-converted DNA?+
Age estimation from methylation markers and tissue or fluid identification (for example distinguishing blood from saliva) both depend on reading methylation patterns at specific loci, which requires the DNA to first go through bisulphite conversion.
Related terms
- Cell-Free DNA (cfDNA)
- Short DNA fragments (~166 bp) circulating extracellularly in body fluids, shed from apoptotic and necrotic cells. In plasma, predominantly hematopoietic; in pregnancy,...
- CpG Methylation
- Addition of a methyl group to cytosine in a CpG dinucleotide. Methylation at age-associated CpGs increases or decreases with chronological age in...
- ELOVL2 Clock
- A forensic age-estimation system based on bisulphite pyrosequencing of 5 CpG sites in the ELOVL2 gene promoter; validated in multiple independent European...
- EPIC Array (Illumina)
- The Infinium MethylationEPIC v2.0 microarray measuring methylation beta values at approximately 935,000 CpG sites genome-wide; the current standard instrument for multi-CpG age-clock...
- EpiTYPER
- Agena Bioscience (formerly Sequenom) reagent system for quantitative methylation analysis via bisulphite PCR and MALDI-TOF mass spectrometry; used for multi-CpG methylation profiling...
- HIrisPlex-S
- A 41-SNP externally visible characteristics (EVC) panel for simultaneous prediction of eye, hair, and skin colour, developed at Erasmus MC Rotterdam by...
- Horvath 353-CpG Clock
- A pan-tissue epigenetic age clock built on the methylation values of 353 CpG sites from the Illumina 450K array; developed by Steve...
- MiRNA (microRNA)
- A small non-coding RNA (21-23 nt) that regulates gene expression post-transcriptionally. Different tissues and body fluids express different miRNA sets; forensic miRNA...