In nuclear biology and molecular biology, a marker gene is a gene used to determine if a nucleic acid sequence has been successfully inserted into an organism's DNA.

1. Marker
Genes
Tasmina Ferdous Susmi
Jessore University of Science and Technology,
Bangladesh

2. Marker gene
Used in molecular biology.
It is a DNA sequence with a
known location on a
chromosome.
Used to determine if a piece of
DNA has been successfully
inserted into the host organism.

3. Characters of Marker Gene
• Represent genetic differences between individual
organisms or species.
• Do not represent the target gene themselves but
act as signs or flag.
• Do not affect the phenotype of the desired genes.
• Occupy specific genomic positions within
chromosomes.

4. Types of marker genes
Marker
Selectable
Marker
Antibiotic
Marker
Non
Antibiotic
Marker
Screenable
Marker
Fluorescen
ce Marker
Colorimetric
assay

5. Types of marker genes
There are two types of marker genes
Antibiotic
resistance
marker
Antimetabolic
marker
Herbicide
resistance
marker
Selectable
markers Fluorescence
marker
Colorimetric
marker
Reporter
markers

6. Selectable marker
Selectable marker is required for
maintenance of plasmid in the
cell.
It is a genes that confers
resistance to particular
antibiotics.
Genes that make cells resistance
to ampicillin, neomycin or
chloramphenicol

7. Characters of Selectable Marker
• Protect the organism from a selective agent that
would normally kill it or prevent its growth.
• Used for killing all cells that donot contain the
foreign DNA.
• Antibiotics are most common selective marker.
• Non Antibiotics Marker can be 2 types
• Endogenous marker
• Nutritional marker

8. List of selectable marker gene, source of
genes and substrate
Selectable marker
gene
Source of genes Substrates
not II E. coli Kanamycin
hpt E.coli Hygromycin
dhfr mouse Methotrexate
epsps Petunia hybrida Glyphosate

9. Reporter marker
• Also known as screenable marker.
• A gene used to ‘tag’ another gene or DNA
sequence, such as promoter.
• Encode gene products whose enzyme activity can
easily be assayed.
• It is used as marker to confirm stable
transformation.

10. Commonly Used Reporter marker
Three types of Screening marker commonly used:
1. Green Fluorescent Protein (GFP)
– Make cells glow green under UV light.
– A specialized microscope is required to see individual
cells.
– Commonly used to measure gene expression.
2. GUS Assay
– Use of beta-glucourinidase.

11. Commonly Used Reporter marker
– AN excellent method for detecting a single cell by
staining it blue.
3. Blue White Screening
– Used in bacteria.
– The lacZ gene makes cells turn blue in special media, e.g.
X-gal
– A colony of cells with the gene can be seen with the
naked eye.

12. List of reporter marker gene, source of
genes and detection assay
Reporter marker
gene
Source of genes Detection assay
ocs Agrobacterium
tumefaciens Electrophoresis
nos Agrobacterium
tumefaciens Electrophoresis
gus E.coli Colorimetric
cat E.coli
Autoradiography

13. Selectable marker vs Reporter marker
Selectable marker Reporter marker
• A gene whose expression
allows one to identify cells
that have been transformed
or transfected with a vector
containing the marker gene
•A gene used to tag another
gene or DNA sequence
• Helps to distinguish between
transformants and non-
transformants
•Helps to measure the amount
of expression of transformed
gene
• Has its own promoter •Regulated under the promoter
of the transformed gene
• Ex:Antibiotic resistance
gene,herbicide resistance
gene
•Ex:GFP and Luciferase