107. Which one of the following sets is an example of specific sequence-based PCR analysis in marker assisted
selection?
(1) RAPD, DAF, AP-PCR P1 P2 F1
(2) SCAR, SSR, COS
(3)SCAR, SSR, DAF
(4) RAPD, SSR, COS

Detailed Explanation:

Question:
Which one of the following sets is an example of specific sequence-based PCR analysis in marker-assisted selection?

Correct Answer:
(2) SCAR, SSR, COS

Understanding Marker-Assisted Selection (MAS)

Marker-Assisted Selection (MAS) is a method in molecular breeding where DNA markers are used to select for desirable traits in plants or animals. A critical aspect of MAS is the use of PCR-based markers that are specific to known sequences. These allow breeders to track genetic loci linked to desired traits accurately.

What is Specific Sequence-Based PCR Analysis?

This form of analysis relies on DNA markers that:

• Are based on known DNA sequences,

• Amplify specific genomic regions,

• Provide reproducible and reliable results.

This makes them ideal for high-precision breeding and selection.

Markers in Option (2):

Let’s break down the markers in Option 2 (Correct Answer):

• SCAR (Sequence Characterized Amplified Region):
  These markers are derived from RAPD or AFLP markers and are converted into more specific and reproducible markers using longer primers designed from sequenced fragments.

• SSR (Simple Sequence Repeats):
  Also known as microsatellites, SSRs are tandem repeats of 1–6 base pairs found throughout the genome. They are co-dominant, highly polymorphic, and locus-specific.

• COS (Conserved Orthologous Sequences):
  COS markers target conserved regions across species, making them excellent tools for comparative mapping and evolutionary studies.

All three of these markers rely on known DNA sequences for amplification—thus they are specific sequence-based.

Why Not the Other Options?

• Option 1: RAPD, DAF, AP-PCR
  These are random amplified markers. They are not sequence-specific and often lack reproducibility.

• Option 3: SCAR, SSR, DAF
  While SCAR and SSR are sequence-specific, DAF (DNA Amplification Fingerprinting) is random and not sequence-based.

• Option 4: RAPD, SSR, COS
  Includes RAPD, which is not based on known sequences.

Conclusion:

For accurate and reproducible results in marker-assisted selection, sequence-specific markers like SCAR, SSR, and COS are preferred. These markers enhance the precision of selection in breeding programs and offer a dependable molecular toolkit for genetic improvement.

✅ Final Answer: (2) SCAR, SSR, COS