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AFLP--Amplified Fragment Length Polymorphism






AFLP is a PCR-based DNA fingerprinting technique combining restriction digestion and selective PCR amplification of genomic DNA fragments.
Developed by Vos et al., 1995.
AFLP detects DNA polymorphisms at the genomic level and is highly reproducible and sensitive.
Used in genetic mapping, diversity studies, phylogenetics, and marker-assisted selection.


Principle


AFLP relies on restriction digestion of genomic DNA, followed by ligation of adaptors and PCR amplification of a subset of fragments.
Polymorphism arises due to variations in restriction sites, fragment length, insertions, or deletions.


Key idea:


Restriction digestion → Adaptor ligation → Selective amplification → Gel separation → Detection of polymorphic bands
Materials Required
Genomic DNA
Restriction enzymes (usually EcoRI and MseI)
Adaptors complementary to restriction sites
PCR reagents: Taq polymerase, dNTPs, buffer, Mg²⁺
Primers complementary to adaptors with selective nucleotides
Thermal cycler
Polyacrylamide or agarose gel electrophoresis system
DNA staining dyes or fluorescent labels


Procedure

Step 1: DNA Isolation

Extract high-quality genomic DNA from tissue, blood, or cells.

Step 2: Restriction Digestion

Digest DNA with two restriction enzymes, usually:
EcoRI (rare cutter, 6-base recognition)
MseI (frequent cutter, 4-base recognition)


Step 3: Adaptor Ligation


Ligate synthetic oligonucleotide adaptors to the sticky ends of DNA fragments.
Adaptors serve as primer binding sites for PCR amplification.


Step 4: Pre-selective PCR Amplification


Use primers complementary to adaptors without selective nucleotides.
Amplifies all fragments ligated to adaptors.
Step 5: Selective PCR Amplification
Use primers with 1–3 selective nucleotides at the 3’ end.
Only a subset of fragments is amplified, generating manageable band numbers.


Step 6: Gel Electrophoresis


Separate amplified fragments on polyacrylamide or high-resolution agarose gel.
Visualize polymorphic bands using fluorescent or radioactive labels.


Step 7: Data Analysis


Score presence (1) or absence (0) of bands.
Use for genetic similarity, diversity, mapping, or phylogenetic studies.


Diagram in Words




Genomic DNA → Restriction Enzyme Digestion (EcoRI + MseI)
      ↓
Ligate Adaptors to Sticky Ends
      ↓
Pre-selective PCR (All fragments)
      ↓
Selective PCR (Subset of fragments)
      ↓
Polyacrylamide Gel Electrophoresis
      ↓
Visualization & Scoring of Polymorphic Bands
Characteristics of AFLP
Highly reproducible
High polymorphism detection
Dominant marker (cannot distinguish heterozygotes from homozygotes)
Genome-wide coverage
Requires no prior sequence information.


Merits of AFLP


Detects high number of polymorphisms per assay
Highly reproducible compared to RAPD
No prior sequence information needed
Can be applied to plants, animals, and microbes
Suitable for population genetics, phylogenetics, and genetic mapping.

Limitations of AFLP


Dominant marker: Cannot distinguish heterozygotes
Technically complex: Requires multiple steps (digestion, ligation, two PCRs)
Expensive: Requires restriction enzymes, primers, and fluorescent labels
Band identification is not locus-specific
Less useful for marker-assisted breeding requiring co-dominant markers.


Applications of AFLP


Genetic diversity and population studies
Phylogenetic and evolutionary studies
Construction of genetic maps
Marker-assisted selection (MAS) in breeding programs
DNA fingerprinting
Detection of somaclonal variation in tissue-cultured plants
Microbial strain typing

Conclusion


AFLP is a powerful, highly sensitive, and reproducible DNA fingerprinting technique.
It is suitable for genome-wide polymorphism analysis in species with unknown genomes.
Limitations include dominance, technical complexity, and cost, but its high-throughput capability makes it a widely used molecular marker in genetics, breeding, and phylogenetics.




1. AFLP stands for:
A. Amplified Fragment Length Polymorphism
B. Arbitrary Fragment Length Polymorphism
C. Amplified Fluorescent Labeled Polymorphism
D. Allele Fragment Length Polymorphism
Answer: A

2. AFLP combines which two techniques?
A. RAPD + RFLP
B. RFLP + SSR
C. PCR + Restriction digestion
D. Southern blot + PCR
Answer: C

3. AFLP was developed in:
A. 1985
B. 1990
C. 1995
D. 2000
Answer: C


4. AFLP is a:
A. Protein marker
B. Dominant DNA marker
C. Co-dominant DNA marker
D. Morphological marker
Answer: B


5. AFLP requires prior DNA sequence information:
A. Yes
B. No
Answer: B
Principle and Procedure
6. AFLP detects polymorphism due to:
A. Restriction site variations
B. Fragment length differences
C. Insertions or deletions
D. All of the above
Answer: D
7. AFLP uses which restriction enzymes commonly?
A. EcoRI and MseI
B. HindIII and BamHI
C. TaqI and PstI
D. None of the above
Answer: A
8. Adaptors are ligated to DNA fragments in AFLP to:
A. Digest DNA
B. Provide primer binding sites
C. Label DNA
D. Visualize DNA
Answer: B
9. AFLP involves how many PCR steps?
A. One
B. Two (pre-selective and selective)
C. Three
D. Four
Answer: B
10. Selective PCR primers in AFLP have:
A. No additional nucleotides
B. 1–3 selective nucleotides at 3’ end
C. 10 extra nucleotides at 5’ end
D. Random length nucleotides
Answer: B
11. AFLP fragments are separated by:
A. Agarose or polyacrylamide gel electrophoresis
B. SDS-PAGE
C. Native PAGE only
D. Capillary electrophoresis
Answer: A
12. Visualization of AFLP bands is commonly done using:
A. Fluorescent dyes
B. Radioactive labeling
C. Silver staining
D. Any of the above
Answer: D
13. AFLP polymorphism is scored as:
A. Homozygote/heterozygote
B. Presence (1) or absence (0)
C. Protein intensity
D. RNA expression
Answer: B
14. AFLP requires DNA of:
A. Very large amount
B. Moderate amount
C. Very small amount
D. RNA contamination
Answer: B
15. AFLP is considered more reproducible than:
A. RAPD
B. SSR
C. RFLP
D. Morphological markers
Answer: A
Advantages
16. AFLP can detect:
A. Hundreds of polymorphic fragments per assay
B. Only a few fragments
C. Single-locus polymorphism only
D. Only protein variation
Answer: A
17. AFLP does not require:
A. Restriction digestion
B. Southern blotting
C. PCR amplification
D. Primers
Answer: B
18. AFLP is suitable for:
A. Plants
B. Animals
C. Microorganisms
D. All of the above
Answer: D
19. AFLP is useful for:
A. Population genetics
B. Phylogenetic studies
C. Marker-assisted selection
D. All of the above
Answer: D
20. AFLP is advantageous because it:
A. Requires no prior genome information
B. Is highly reproducible
C. Detects genome-wide polymorphism
D. All of the above
Answer: D
Limitations
21. AFLP is a:
A. Co-dominant marker
B. Dominant marker
Answer: B
22. AFLP cannot distinguish:
A. Polymorphic fragments
B. Homozygotes from heterozygotes
C. Genetic diversity
D. Band pattern differences
Answer: B
23. AFLP requires:
A. Restriction enzymes, ligation, and two PCRs
B. Only PCR
C. Only Southern blotting
D. Only primers
Answer: A
24. AFLP is:
A. Simple and cheap
B. Technically complex and expensive
C. Dominant and locus-specific
D. Co-dominant and fast
Answer: B
25. AFLP fragments are generally:
A. Locus-specific
B. Randomly distributed
Answer: B
Applications
26. AFLP is widely used for:
A. Genetic mapping
B. Phylogenetics
C. Population studies
D. All of the above
Answer: D
27. AFLP is used in plants for:
A. Variety identification
B. Disease resistance mapping
C. Hybrid verification
D. All of the above
Answer: D
28. AFLP can detect:
A. Somaclonal variation
B. DNA fingerprinting
C. Genome-wide polymorphisms
D. All of the above
Answer: D
29. AFLP is suitable for species with:
A. Unknown genome sequences
B. Fully sequenced genomes only
Answer: A
30. AFLP has largely replaced RAPD for:
A. Low-resolution studies
B. High-resolution fingerprinting
Answer: B
Technical Knowledge
31. AFLP pre-selective PCR uses:
A. Primers complementary to adaptors only
B. Primers with selective nucleotides
Answer: A
32. Selective PCR uses primers with:
A. No selective nucleotides
B. 1–3 selective nucleotides
Answer: B
33. AFLP is sensitive to:
A. PCR conditions
B. DNA quality
C. Enzyme activity
D. All of the above
Answer: D
34. AFLP is a:
A. Hybridization-based technique
B. PCR-based technique
Answer: B
35. AFLP produces:
A. Few bands
B. Hundreds of bands per assay
Answer: B
Comparison with Other Markers
36. Compared to RAPD, AFLP is:
A. Less reproducible
B. More reproducible
Answer: B
37. Compared to RFLP, AFLP:
A. Is PCR-based and faster
B. Requires Southern blot
Answer: A
38. Compared to SSR, AFLP:
A. Requires prior sequence info
B. Does not require prior sequence info
Answer: B
39. AFLP is dominant, whereas SSR is:
A. Dominant
B. Co-dominant
Answer: B
40. AFLP is preferred for:
A. High-resolution genome-wide studies
B. Low-resolution studies
Answer: A
Advanced Applications
41. AFLP is useful in:
A. Plant breeding programs
B. Animal population studies
C. Microbial strain typing
D. All of the above
Answer: D
42. AFLP data is usually analyzed using:
A. Binary scoring of bands
B. Protein gels
C. RNA profiling
Answer: A
43. AFLP is highly suitable for:
A. Phylogenetic studies of closely related species
B. Morphological analysis
Answer: A
44. AFLP allows:
A. Detection of large and small fragment polymorphisms
B. Detection of only large fragments
Answer: A
45. AFLP is widely used in:
A. Forensic science
B. Conservation biology
C. Genetic mapping
D. All of the above
Answer: D
Miscellaneous
46. AFLP requires:
A. Restriction digestion
B. Adaptor ligation
C. Two PCR steps
D. All of the above
Answer: D
47. AFLP primers are designed:
A. Randomly complementary to adaptors
B. From coding regions only
Answer: A
48. AFLP polymorphism arises due to:
A. Variation in restriction sites
B. Sequence insertions/deletions
C. Mutations at primer binding sites
D. All of the above
Answer: D
49. AFLP produces:
A. Reproducible fingerprints
B. Irreproducible patterns
Answer: A
50. AFLP is considered more advanced than RAPD because:
A. Higher reproducibility
B. Higher resolution
C. Genome-wide coverage
D. All of the above
Answer: D

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