Skip to main content

Molecular Marker Techniques


Molecular Marker Techniques (30-Mark Detailed Notes)


Introduction

Molecular markers are DNA sequences with known locations on chromosomes that can be used to identify individuals, genotypes, or genetic differences. They reveal polymorphism at the DNA level and are not influenced by environmental factors, unlike morphological or biochemical markers.
Molecular marker techniques are widely used in genetics, plant breeding, biotechnology, forensics, medical diagnosis, and evolutionary studies.


Characteristics of an Ideal Molecular Marker


An ideal molecular marker should:
Be highly polymorphic
Show co-dominant inheritance
Be abundant and uniformly distributed in the genome
Be environment-independent
Have high reproducibility
Be easy, rapid, and cost-effective
Classification of Molecular Marker
  Techniques


1. Hybridization-Based Markers


RFLP (Restriction Fragment Length Polymorphism)

2. PCR-Based Markers

RAPD
AFLP
SSR (Microsatellites)
ISSR

3. Sequence-Based Markers

SNP (Single Nucleotide Polymorphism)
1. Restriction Fragment Length Polymorphism (RFLP)

Principle

RFLP is based on variation in DNA fragment lengths produced by digestion with restriction enzymes, followed by Southern blotting and probe hybridization.

Steps

Isolation of genomic DNA
Digestion with restriction endonucleases
Agarose gel electrophoresis
Southern blot transfer
Hybridization with labeled probe
Autoradiography

Merits

Co-dominant marker
Highly reproducible
Locus specific

Demerits
Requires large amount of DNA
Time-consuming and labor-intensive
Uses radioactive probes
Applications
Genetic mapping
DNA fingerprinting
Detection of disease genes
2. Random Amplified Polymorphic DNA (RAPD)

Principle
RAPD uses short arbitrary primers (10 bp) to amplify random DNA segments using PCR. Polymorphism arises due to presence or absence of primer binding sites.
Steps
DNA isolation
PCR amplification using random primers
Agarose gel electrophoresis
Band pattern analysis


Merits


Rapid and simple
Requires small amount of DNA
No prior sequence information required


Demerits
Dominant marker
Low reproducibility
Sensitive to PCR conditions
Applications
Genetic diversity analysis
Species identification
Population studies
3. Amplified Fragment Length Polymorphism (AFLP)

Principle
AFLP combines restriction digestion and selective PCR amplification of fragments.
Steps
DNA digestion with restriction enzymes
Ligation of adaptors
Pre-selective amplification
Selective amplification
Gel electrophoresis
Merits

High reproducibility
Detects high level of polymorphism
No sequence information required
Demerits
Dominant marker
Technically complex
Expensive

Applications
Linkage mapping
DNA fingerprinting
Genetic diversity analysis
4. Simple Sequence Repeat (SSR / Microsatellite)

Principle
SSR markers are based on variation in the number of short tandem repeats (1–6 bp) in DNA.
Steps
Primer design flanking SSR region
PCR amplification
Polyacrylamide/agarose gel analysis

Merits

Co-dominant
Highly polymorphic
Highly reproducible

Demerits

Requires sequence information
Primer development is costly
Applications
Marker-assisted selection
Genetic mapping
Variety identification
5. Inter Simple Sequence Repeat (ISSR)
Principle

ISSR amplifies DNA between two microsatellite regions using a single primer.
Merits
High polymorphism
No prior sequence data needed
Better reproducibility than RAPD
Demerits
Dominant marker
Limited locus specificity
6. Single Nucleotide Polymorphism (SNP)


Principle
SNPs represent single base changes in DNA sequences and are detected by sequencing or allele-specific assays.


Merits

Abundant in genome
Highly stable
Suitable for automation
Demerits
Bi-allelic (low polymorphism per locus)
Requires advanced technology

Applications

Genome-wide association studies
Medical diagnostics
Evolutionary studies


Applications of Molecular Marker Techniques


Genetic diversity and phylogenetic analysis
Marker-assisted breeding
Disease resistance gene identification
DNA fingerprinting and forensics
QTL mapping
Conservation biology

Advantages 

Environment-independent
Highly accurate
Early selection possible
Applicable to all life stages

Limitations

High cost (advanced markers)
Technical expertise required
Dominant markers cannot distinguish heterozygotes

Conclusion

Molecular marker techniques are powerful tools in modern biology, enabling precise analysis of genetic variation. The choice of marker depends on purpose, cost, reproducibility, and resolution required. Advanced markers like SSR and SNP have revolutionized plant breeding, medical genetics, and genomic research.


Molecular Marker Techniques – 50 MCQs with Answers

1. Molecular markers are:
A. Protein markers
B. RNA markers
C. DNA sequences with known location
D. Lipid molecules
Answer: C
2. Which of the following is an ideal property of a molecular marker?
A. Environment dependent
B. Low polymorphism
C. Co-dominant inheritance
D. Tissue specific
Answer: C
3. Which was the first DNA-based molecular marker?
A. RAPD
B. AFLP
C. RFLP
D. SSR
Answer: C
4. RFLP analysis requires:
A. PCR amplification
B. Southern blotting
C. Northern blotting
D. Western blotting
Answer: B
5. RFLP is detected by:
A. Sequencing
B. Hybridization with probes
C. ELISA
D. Staining with antibodies
Answer: B
6. RFLP markers are:
A. Dominant
B. Co-dominant
C. Recessive
D. Neutral
Answer: B
7. RAPD uses primers of length:
A. 5 bp
B. 10 bp
C. 20 bp
D. 50 bp
Answer: B
8. RAPD markers are:
A. Co-dominant
B. Dominant
C. Locus specific
D. Highly reproducible
Answer: B
9. RAPD does NOT require:
A. PCR
B. DNA isolation
C. Sequence information
D. Agarose gel electrophoresis
Answer: C
10. RAPD polymorphism arises due to:
A. Mutation in coding genes
B. Variation in primer binding sites
C. Protein modification
D. RNA splicing
Answer: B
11. AFLP is a combination of:
A. PCR and sequencing
B. Restriction digestion and PCR
C. Hybridization and blotting
D. ELISA and PCR
Answer: B
12. AFLP markers are mostly:
A. Co-dominant
B. Dominant
C. Recessive
D. Mitochondrial
Answer: B
13. Which marker shows the highest reproducibility?
A. RAPD
B. RFLP
C. AFLP
D. ISSR
Answer: B
14. SSR markers are also known as:
A. Minisatellites
B. SNPs
C. Microsatellites
D. Isotopes
Answer: C
15. SSR polymorphism is due to:
A. Single base change
B. Restriction site variation
C. Variation in repeat number
D. Protein folding
Answer: C
16. SSR markers are:
A. Dominant
B. Co-dominant
C. Environment dependent
D. Unstable
Answer: B
17. ISSR primers anneal to:
A. Coding regions
B. Restriction sites
C. Microsatellite repeats
D. Promoter regions
Answer: C
18. ISSR markers are:
A. Co-dominant
B. Dominant
C. Protein-based
D. RNA-based
Answer: B
19. SNP stands for:
A. Single Nuclear Protein
B. Short Nucleotide Polymorphism
C. Single Nucleotide Polymorphism
D. Sequence Number Pattern
Answer: C
20. SNP markers are:
A. Multi-allelic
B. Rare in genome
C. Highly abundant
D. Environment dependent
Answer: C
21. Which marker is MOST suitable for automation?
A. RAPD
B. RFLP
C. SNP
D. ISSR
Answer: C
22. Which marker requires the least amount of DNA?
A. RFLP
B. RAPD
C. AFLP
D. SSR
Answer: B
23. Which marker requires radioactive labeling?
A. RAPD
B. AFLP
C. RFLP
D. ISSR
Answer: C
24. Which technique is used in DNA fingerprinting?
A. RAPD
B. RFLP
C. SSR
D. All of the above
Answer: D
25. QTL mapping commonly uses:
A. Protein markers
B. Morphological markers
C. Molecular markers
D. Chemical markers
Answer: C
26. Which marker is locus specific?
A. RAPD
B. AFLP
C. RFLP
D. ISSR
Answer: C
27. Which is NOT a PCR-based marker?
A. RAPD
B. AFLP
C. SSR
D. RFLP
Answer: D
28. ISSR technique is an improvement over:
A. AFLP
B. RFLP
C. RAPD
D. SNP
Answer: C
29. Which marker shows highest polymorphism per locus?
A. SNP
B. RFLP
C. SSR
D. RAPD
Answer: C
30. Which marker is bi-allelic?
A. SSR
B. SNP
C. AFLP
D. ISSR
Answer: B
31. Molecular markers are not affected by:
A. Environment
B. Temperature
C. Developmental stage
D. All of the above
Answer: D
32. Which marker is best for population genetics?
A. SSR
B. SNP
C. RAPD
D. Both A and B
Answer: D
33. AFLP fragments are detected by:
A. Autoradiography
B. Gel electrophoresis
C. ELISA
D. Spectrophotometry
Answer: B
34. SSR primers are designed from:
A. Protein sequences
B. Known DNA sequences
C. RNA sequences
D. Amino acids
Answer: B
35. Which marker is most expensive?
A. RAPD
B. RFLP
C. SNP
D. ISSR
Answer: C
36. Which marker is highly suitable for marker-assisted selection?
A. RAPD
B. SSR
C. ISSR
D. RFLP
Answer: B
37. Molecular markers help in:
A. Gene tagging
B. Linkage analysis
C. Variety identification
D. All of the above
Answer: D
38. Dominant markers cannot:
A. Detect polymorphism
B. Amplify DNA
C. Distinguish heterozygotes
D. Be PCR-based
Answer: C
39. Which marker involves adaptor ligation?
A. RAPD
B. SSR
C. AFLP
D. ISSR
Answer: C
40. Which technique combines restriction digestion and selective amplification?
A. RFLP
B. RAPD
C. AFLP
D. SSR
Answer: C
41. Which marker is best for evolutionary studies?
A. SNP
B. SSR
C. RAPD
D. ISSR
Answer: A
42. Molecular markers can be used at:
A. Seedling stage
B. Adult stage
C. Any developmental stage
D. Only flowering stage
Answer: C
43. Which marker detects variation at a single base?
A. RAPD
B. SSR
C. SNP
D. AFLP
Answer: C
44. Which marker shows low polymorphism per locus?
A. SSR
B. RFLP
C. SNP
D. AFLP
Answer: C
45. Which technique uses microsatellite repeats as primers?
A. SSR
B. RAPD
C. ISSR
D. AFLP
Answer: C
46. Molecular markers are useful in conservation biology for:
A. Species identification
B. Genetic diversity analysis
C. Phylogenetic studies
D. All of the above
Answer: D
47. Which marker does NOT require Southern blotting?
A. RFLP
B. RAPD
C. Both B and C
D. Only A
Answer: B
48. Which molecular marker is multi-allelic?
A. SNP
B. RAPD
C. SSR
D. AFLP
Answer: C
49. Which marker technique is least reproducible?
A. SSR
B. AFLP
C. RAPD
D. RFLP
Answer: C
50. Molecular markers mainly detect:
A. Phenotypic variation
B. Environmental variation
C. Genetic variation
D. Metabolic variation
Answer: C


Labels:

Comments

Post a Comment

Popular Posts

Electroporation – Detailed Notes

Electroporation – Detailed Notes Definition : Electroporation is a physical method of gene transfer in which cells are exposed to a brief, high-voltage electric pulse, creating temporary pores in the cell membrane. This allows DNA, RNA, proteins, or other molecules to enter the cytoplasm. It is widely used in bacteria, yeast, plant protoplasts, and mammalian cells. Key Concept: The electric field destabilizes the membrane, making it permeable to macromolecules. 1. Principle Cells are suspended in a conductive medium. A brief electrical pulse induces transient pores in the plasma membrane. DNA or other molecules present in the medium enter the cell through these pores. Membrane reseals after the pulse, and the molecule is retained inside the cell. Advantages of Principle: Direct and rapid. Works in many cell types. Does not require chemical carriers or viral vectors. 2. Materials Required Cells – bacterial, yeast, plant protoplasts, mammalian cells. DNA/RNA/other macromolecule – purifie...
Post a Comment
Read more

Protein Structure Database (PDB)

Protein Structure Database (PDB) Introduction The Protein Structure Database (PDB) is the primary global repository for the three-dimensional (3D) structures of biological macromolecules such as proteins, nucleic acids, and protein–ligand complexes. These structures are determined experimentally using techniques like X-ray crystallography, Nuclear Magnetic Resonance (NMR) spectroscopy, and Cryo-Electron Microscopy (Cryo-EM). PDB plays a vital role in understanding: Protein structure and function Molecular interactions Drug discovery and design Structural biology and bioinformatics History and Development Established in 1971 Founded by Brookhaven National Laboratory (USA) Initially contained only 7 protein structures Now maintained by the Worldwide Protein Data Bank (wwPDB) Members of wwPDB RCSB PDB (USA) PDBe (Europe) PDBj (Japan) BMRB (Biological Magnetic Resonance Data Bank) Objectives of PDB To collect, store, and distribute 3D structural data of biomolecules To provide free and ope...
Post a Comment
Read more

Information retrieval from databases - search concepts, Tools for searching, homology searching, finding Domain and Functional site homologies

Information retrieval from databases - search concepts, Tools for searching, homology searching, finding Domain and Functional site homologies Information Retrieval from Databases 1. Introduction Information retrieval in bioinformatics refers to the process of extracting relevant biological data (DNA, RNA, protein sequences, structures, or functional information) from databases. Aim : Identify sequences, functions, or structural features for analysis, comparison, and annotation. Databases can be primary (raw sequence data) or secondary/derived (annotated, processed data). 2. Search Concepts in Biological Databases 2.1 Types of Searches Exact Match Search Returns results only if the query exactly matches database entries. Useful for known accession numbers or IDs. Pattern/Keyword Search Searches based on specific motifs, keywords, or annotations. Example: “kinase domain,” “signal peptide.” Similarity/Homology Search Detects sequences similar to the query based on sequence alignment. Use...
Post a Comment
Read more

π“†ž Western Blotting Notes

Western Blotting (Immunoblotting) ❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥  Introduction Western blotting, also known as immunoblotting, is a widely used analytical technique for the detection, identification, and quantification of specific proteins in a complex biological sample. The technique combines protein separation by gel electrophoresis with specific antigen–antibody interaction. The method was developed by Towbin et al. (1979) (Burnette 1981---its group work) and is called “Western” in analogy to Southern blotting (DNA) and Northern blotting (RNA). Principle The principle of Western blotting involves: Separation of proteins based on molecular weight using SDS-PAGE Transfer (blotting) of separated proteins onto a membrane Specific detection of the target protein using primary and secondary antibodies Visualization using enzymatic or fluorescent detection systems πŸ‘‰ Antigen–antibody specificity is the core principle of Western blotting. Steps Involved in Western Blotting 1. Sa...
Post a Comment
Read more

••CLASSIFICATION OF ALGAE - FRITSCH

      MODULE -1       PHYCOLOGY  CLASSIFICATION OF ALGAE - FRITSCH  ❖F.E. Fritsch (1935, 1945) in his book“The Structure and  Reproduction of the Algae”proposed a system of classification of  algae. He treated algae giving rank of division and divided it into 11  classes. His classification of algae is mainly based upon characters of  pigments, flagella and reserve food material.     Classification of Fritsch was based on the following criteria o Pigmentation. o Types of flagella  o Assimilatory products  o Thallus structure  o Method of reproduction          Fritsch divided algae into the following 11 classes  1. Chlorophyceae  2. Xanthophyceae  3. Chrysophyceae  4. Bacillariophyceae  5. Cryptophyceae  6. Dinophyceae  7. Chloromonadineae  8. Euglenineae    9. Phaeophyceae  10. Rhodophyceae  11. Myxophyce...
Post a Comment
Read more

✩‧₊ Plaque Blotting Technique

Plaque Blotting Technique *ੈ✩‧₊˚༺☆༻*ੈ✩‧₊˚*ੈ✩‧₊˚༺☆༻*ੈ✩‧₊˚ Introduction Plaque blotting is a molecular biology screening technique used to identify specific DNA or RNA sequences present in bacteriophage plaques formed on a bacterial lawn. It is especially useful in the screening of recombinant phage libraries such as Ξ» (lambda) phage genomic or cDNA libraries. This technique combines: Plaque assay (to isolate individual phage clones) Blotting technique (to transfer nucleic acids onto a membrane) Hybridization (to detect specific sequences using labeled probes) Principle of Plaque Blotting The principle of plaque blotting is based on nucleic acid hybridization. Each plaque represents a clone of phage particles containing identical DNA. DNA from phage particles in plaques is: Released Denatured into single strands Transferred onto a nitrocellulose or nylon membrane The membrane is incubated with a labeled DNA/RNA probe complementary to the target sequence. Hybridization between probe and t...
Post a Comment
Read more