Step 1: Context of HAT medium.
HAT medium is used in hybridoma technology to select hybrid cells (hybridomas) that produce monoclonal antibodies. It was developed by Littlefield in 1964.
Step 2: What does HAT stand for?
HAT = Hypoxanthine, Aminopterin, Thymidine. Each component serves a specific purpose.
Step 3: How the selection works.
Aminopterin blocks the de novo synthesis of purines and pyrimidines. Cells that survive must use the salvage pathway, which requires hypoxanthine (for purines) and thymidine (for pyrimidines).
Step 4: Why only hybridomas survive.
Unfused myeloma cells have no salvage pathway, so they die in HAT. Unfused B-cells cannot survive long in culture. Only hybridomas (fused B-cell + myeloma) have both the salvage enzymes from the B-cell and the ability to grow indefinitely from the myeloma, so only they survive.
Step 5: Eliminate wrong options.
Option 1 (Heparin, ATP, Threonine) and Option 2 (Histidine, Alanine, Thymine) are fabricated combinations. Option 4 mixes up the letters with wrong molecules.
Answer: Option (3) — Hypoxanthine, Aminopterin, Thymidine