Aquaculture & Marine Biotechnology

• Properties and Action of TdT:
• Terminal Deoxynucleotidyl Transferase (TdT) is a template-independent DNA polymerase.
• It catalyzes the repetitive addition of deoxynucleoside triphosphates (dNTPs) onto the $3'\text{-OH}$ terminus of single-stranded or double-stranded DNA molecules without requiring a template strand.
• Biotechnological Applications:
• Used in homopolymer tailing (e.g., adding poly-dG or poly-dC tails to vectors and cDNAs for blunt-end cloning).
• Labeling $3'$ ends of DNA with radioactive nucleotides or digoxigenin for non-radioactive probes.
• TUNEL assay for detecting apoptotic DNA fragmentation.
• nalysis:
• (Terminal Deoxynucleotidyl Transferase): Correct.

Correct option: (4) Terminal Deoxynucleotidyl Transferase

• RNA Interference (RNAi):
• First discovered in C. elegans by Andrew Fire and Craig Mello (1998, Nobel Prize 2006):
• RNA interference is an evolutionarily conserved post-transcriptional gene silencing mechanism where short double-stranded RNA molecules trigger sequence-specific mRNA degradation.
• Exogenous or endogenous double-stranded RNA is cleaved by the ribonuclease Dicer into $\approx 21-23\text{ bp}$ small interfering RNAs (siRNAs).
• siRNAs are loaded into the RISC (RNA-Induced Silencing Complex), unwound to a guide strand, and direct the endonuclease Argonaute (Ago2) to cleave complementary target mRNAs.
• nalysis:
• (RNA interference): Correct.

Correct option: (3) RNA interference