Marker-assisted selection (MAS) is a plant breeding method that uses molecular markers linked to traits of interest to guide selection for desirable crop traits. It allows breeders to select plants earlier in the breeding cycle compared to phenotypic selection alone. MAS has advantages like being unaffected by environmental conditions and enabling selection for recessive traits. However, it also has drawbacks like being more expensive than conventional techniques and the possibility of recombination between markers and traits. Careful analysis of costs and benefits is needed to determine when MAS is advantageous compared to conventional breeding methods.

1. Marker Assisted Selection
By
Kartikey Sootrakar
Ph.D. IIIrd semester
Enroll. 170234001
College of Agriculture, Rewa
J.N.K.V.V., Jabalpur (M.P.)
Doctoral Seminar
on

2. Marker-Assisted Selection
A method of selecting desirable individuals
in a breeding scheme
patterns
based
instead
on
of,
DNA
molecular marker or in
addition to, their trait values.
A tool that can help plant breeders select
more efficiently for desirable crop traits.
MAS is not always advantageous, so careful
relativeanalysis of the costs and benefits
to conventional breeding methods is
necessary.

3. CONVENTIONAL PLANT BREEDING
P1 P2x
DonorRecipient
F1
large populations consisting of
thousands of plantsF2
PHENOTYPIC SELECTION
Bacterial blight screening Phosphorus deficiency plotSalinity screening in phytotron
Field trialsGlasshouse trials

4. MARKER-ASSISTED BREEDING
P1 x P2
Susceptible Resistant
F1
large populations consisting of
F2
thousands of plants
MARKER-ASSISTED SELECTION (MAS)
Method whereby phenotypic selection is based on DNA markers

5. Prerequisites for an efficient marker-assisted
selection program
High throughput DNA
extraction

6. Markers
Markers (morphological, protein, cytological)
also be used in MAS programs.
can
RFLP, SSR, RAPD, AFLP,and SNP
For efficient
 Ease of use
Small amount
Low cost
Repeatability
MAS:
of DNA required
of results
 High rate of polymorphism
Occurrence throughout the genome
Codominance

7. gene.
Genetic maps
Linkage maps provide a framework for detecting
marker-trait associations and for choosing markers
to employ in MAS.
Once a marker is found to be associated with a trait
in a given population, a dense molecular marker map
in a standard reference population will help identify
markers that are closer to, or that flank, the target.

8. Data managementsystem
Large numbers of samples are handled
sample
multiple
in a MAS program, with each
potentially
markers.
evaluated for
This situation requires an efficient
retrieving,system for labeling, storing,
and analyzing large data
useful
sets,
to
and
theproducing
breeder.
reports

9. Potential advantages of MAS
It can be performed on seedling material
Thus reducing the time required before a plant’s
genotype is known.
In contrast, many important plant traits are
observable only when the plant has reached
flowering or harvest maturity.
Knowing a plant’s genotype before
order
flowering can
thebe particularly useful in to plan
appropriate crosses between selected individuals.

10. MAS is not affected by environmental
conditions
Some crop production constraints (such as
disease, insect pests, temperature and moisture
stress) occur sporadically or non-uniformly.
Therefore, evaluating resistance to those
constraints may not be possible in a given year or
location.
MAS offers the chance to determine a plant’s
resistance level independent of environment.

11. When recessive alleles determine traits of
interest
They cannot be detected through phenotypic
evaluation of heterozygous plants, because their
presence is masked by the dominant allele.
In a traditional backcross program, plants with
recessive alleles are identified by progeny
evaluation after self-pollination or testcrossing
recessive tester.
to a
This time-consuming step can be eliminated in a
MAS program, because recessive alleles are
identified by linked markers.

12. When multiple resistance genes are
pyramided together
line,
in the same variety
or breeding
The presence of each individual gene is
difficult to verify phenotypically.
The presence of one resistance gene may
conceal the effect of additional genes.
This problem can
for
be overcome if markers
are available each of the resistance
genes.

13. A consideration that
MAS
may
is
affect cost
effectiveness of
be
that multiple
markers can evaluated using the same
DNA sample.
Once DNA is extracted and purified, it may
same
be
orused for multiple
traits,
markers, for the
different thus reducing the time and
cost per marker.
MAS may be cheaper and faster than
conventional phenotypic assays, depending on
the trait.

14. MAS maybe more expensive than conventional
techniques,
labor costs.
especially for startup expenses and
Recombination between the marker
leading
and the
gene of interest may occur, to false
positives.
 Linkage maps of two chromosomes showing
positions of two resistance genes and nearby
markers.
Drawbacks of MAS

15. Conducting a MAS
(1) TISSUE
SAMPLINGprogram
(2) DNA
EXTRACTION
(3) PCR
(4) GEL
ELECTROPHORESIS
(5) MARKER
ANALYSIS

16. A variety of approaches
MAS: MARKER-ASSISTED SELECTION
- Plants are selected for one or more (up to 8-10) alleles
MABC:
One
to
MARKER-ASSISTED BACKCROSSING
or more (up to 6-8) donor alleles are transferred
an elite line
MARS: MARKER-ASSISTED RECURRENT SELECTION
Selection for several (up to 20-30) mapped QTLs relies
on index (genetic) values computed for each individual
based on its haplotype at target QTLs

17. Conclusion
MAS is a methodology that has already
proved its value.
It is likely to become more valuable as a
larger number of genes are identified and
their functions and interactions elucidated.
Reduced costs and optimized strategies for
integrating MAS with phenotypic selection
are needed before the technology can reach
its full potential.