• In Situ Hybridization (ISH) in Disease Diagnosis:
• In Situ Hybridization (ISH): A molecular diagnostic cytogenetic technique that utilizes labelled (fluorophore- or digoxigenin-tagged) single-stranded complementary DNA or RNA probes to hybridize specifically with target pathogen nucleic acid sequences directly within intact, formalin-fixed, paraffin-embedded tissue sections.
• It permits precise spatial localization and histological visualization of viral or bacterial pathogens (e.g., WSSV, IHHNV) within infected host cell nuclei or cytoplasm under a light/fluorescent microscope.
• Correct Option: Option 2 (In situ hybridization).

• PCR Primer Design for cDNA:
• In molecular biology and RT-PCR:
• The Forward Primer hybridizes to the complementary anti-sense strand, matching the sequence at the $5'$ end of the coding cDNA.
• The Reverse Primer hybridizes to the sense strand and is complementary to the sequence at the $3'$ end of the cDNA coding sequence.
• Correct Option: Option 3 (3' end of cDNA).

• Epigenetic Mechanisms:
• Epigenetics refers to heritable modifications in gene expression that do not involve alterations to the underlying DNA nucleotide sequence.
• Methylation: The addition of methyl groups ($-CH_3$) from S-adenosylmethionine (SAM) that targets:

• DNA: Direct covalent cytosine methylation at CpG dinucleotides catalyzed by DNA methyltransferases (DNMTs) to form 5-methylcytosine ($5\text{mC}$), typically mediating transcriptional silencing.
• Histone Proteins: Methylation of specific lysine ($K$) and arginine ($R$) residues on histone tails (e.g., $H3K4$, $H3K9$, $H3K27$) catalyzed by histone methyltransferases (HMTs).
  • nalysis:

• (Methylation): Correct. Modifies both DNA and histones.
• Options 2 & 4 (Acetylation, Deacetylation): Act on histone lysine residues, not directly on DNA nucleotides.

• Methods of Nucleic Acid and Protein Sequencing:
• DNA Sequencing Methods:
• Maxam-Gilbert Method: Chemical cleavage method using dimethyl sulfate and hydrazine.
• Sanger Sequencing: Dideoxy chain termination method.
• Pyrosequencing: Sequencing-by-synthesis based on detection of released pyrophosphate ($PPi$).
• Illumina (Solexa): Next-generation reversible dye-terminator sequencing.
• Edman Degradation: A classic biochemical method for sequencing amino acids in a peptide/protein from the N-terminus, using phenylisothiocyanate (PITC). It is NOT a DNA sequencing method.
• nalysis:
• (Edman degradation): Correct (it sequences proteins, not DNA).

Correct option: (1) Edaman degradation