Choose the correct answer from the options given below:

1. (A) – (I), (B) – (II), (C) – (III), (D) – (IV)
2. (A) – (I), (B) – (III), (C) – (II), (D) – (IV)
3. (A) – (I), (B) – (II), (C) – (IV), (D) – (III)
4. (A) – (III), (B) – (IV), (C) – (I), (D) – (II)

   Genomics uses specialized techniques to construct physical maps of DNA, each with distinct features for ordering genes and markers.

   Correct Answer

   (A) – (III), (B) – (IV), (C) – (I), (D) – (II)

   Label	Procedure	Correct Feature	Key Application
   A	Radiation hybrid mapping	III. Fragment genome into large pieces and locate markers/genes	Whole-genome ordering via radiation breaks
   B	Sequence tagged site (STS) mapping	IV. Applicable to any DNA sequence if some sequence info available	PCR-based landmark mapping
   C	Chromosome jumping	I. DNA cut into large fragments, circularized for chromosome walking	Long-distance leaps (~100kb jumps)
   D	Chromosome walking	II. Useful for cloning overlapping DNA fragments (~200kb)	Stepwise contig extension from known sequence

   Each Technique Explained

   A. Radiation hybrid mapping → III

   Irradiates chromosomes to create random breaks, fuses fragments into hybrid cells. Retention frequency maps marker order across large genomic regions.

   ✅ Fragments genome for marker/gene positioning.

   B. Sequence tagged site (STS) mapping → IV

   Uses unique short DNA sequences (amplified by PCR) as landmarks. Requires some initial sequence data for primer design.​

   ✅ Universal if sequence known.

   C. Chromosome jumping → I

   Creates large DNA fragments (>100kb) via rare-cutting enzymes, circularizes for cloning. Enables “jumps” to distant regions for walking initiation.

   ✅ Large fragments for jumping ahead.

   D. Chromosome walking → II

   Progressive cloning of overlapping fragments (~40-200kb) from a known probe/STS toward target gene. Limited by library insert size.

   ✅ Overlapping clones within ~200kb range.

   All Options Analysis

   (A)-(I), (B)-(II), (C)-(III), (D)-(IV)

   Radiation hybrids ≠ large fragment circularization (that’s jumping); STS ≠ overlapping clones.​

   ❌ Wrong: Swaps radiation hybrid/jumping roles.

   (A)-(I), (B)-(III), (B)-(II), (D)-(IV)

   Radiation hybrid ≠ jumping fragments; STS ≠ genome fragmentation.​

   ❌ Wrong: Mismatches core techniques.

   (A)-(I), (B)-(II), (C)-(IV), (D)-(III)

   Radiation hybrid ≠ jumping; jumping ≠ STS applicability; walking ≠ large fragmentation.​

   ❌ Wrong: Multiple swaps.

   (A)-(III), (B)-(IV), (C)-(I), (D)-(II)

   Precise: RH fragments genomes, STS sequence-based, jumping leaps with large clones, walking overlaps small steps.

   ✅ Correct option.

   Exam Mnemonic: RH = Fragment (III), STS = Sequence (IV), Jump = Large (I), Walk = Overlap (II).