A new genomic sequencing technique has been developed to detect methylated cytosines in DNA with high sensitivity. This method uses sodium bisulphite to convert cytosine residues to uracil in single-stranded DNA, while 5-methylcytosine (5-MeC) remains non-reactive. The converted DNA is amplified with specific primers and sequenced. All cytosine residues remaining in the sequence represent previously methylated cytosines in the genome. The method allows for the identification of 5-MeC residues by their distinct bands on a sequencing gel. The technique is highly sensitive, capable of detecting methylation patterns in DNA isolated from fewer than 100 cells. The method involves bisulphite conversion, PCR amplification, cloning, and sequencing. Optimization of reaction conditions, including denaturation, bisulphite treatment, desalting, alkali treatment, primer design, and PCR amplification, is crucial for the success of the method. The bisulphite genomic sequencing method is sensitive enough to analyze methylation patterns in DNA isolated from as few as 200pg of genomic DNA. The method provides a positive test for methylation, with each 5-MeC residue indicated by a distinct band on a sequencing gel. The method has potential applications in studying methylation in developmental processes, cancer, and inherited diseases. The technique is particularly useful for identifying methylation patterns in single DNA strands within a population of molecules. The method allows for the analysis of methylation status of individual cytosine residues and provides insights into methylation profiles. The method has been optimized for sensitivity and reproducibility, making it a valuable tool for studying methylation in genomic DNA.A new genomic sequencing technique has been developed to detect methylated cytosines in DNA with high sensitivity. This method uses sodium bisulphite to convert cytosine residues to uracil in single-stranded DNA, while 5-methylcytosine (5-MeC) remains non-reactive. The converted DNA is amplified with specific primers and sequenced. All cytosine residues remaining in the sequence represent previously methylated cytosines in the genome. The method allows for the identification of 5-MeC residues by their distinct bands on a sequencing gel. The technique is highly sensitive, capable of detecting methylation patterns in DNA isolated from fewer than 100 cells. The method involves bisulphite conversion, PCR amplification, cloning, and sequencing. Optimization of reaction conditions, including denaturation, bisulphite treatment, desalting, alkali treatment, primer design, and PCR amplification, is crucial for the success of the method. The bisulphite genomic sequencing method is sensitive enough to analyze methylation patterns in DNA isolated from as few as 200pg of genomic DNA. The method provides a positive test for methylation, with each 5-MeC residue indicated by a distinct band on a sequencing gel. The method has potential applications in studying methylation in developmental processes, cancer, and inherited diseases. The technique is particularly useful for identifying methylation patterns in single DNA strands within a population of molecules. The method allows for the analysis of methylation status of individual cytosine residues and provides insights into methylation profiles. The method has been optimized for sensitivity and reproducibility, making it a valuable tool for studying methylation in genomic DNA.