MAS (MARKER ASSISTED SELECTION ) AGB PPT RAMESH KUMAR.pptx

1. RAJASTHAN UNIVERSITY OF VETERINARYAND ANIMAL SCIENCES
(BIKANER)
POST GRADUATE INSTITUTE OF VETERINARY
EDUCATION AND RESEARCH, JAIPUR
DEPARTMENT OF VETERINARY ANIMAL GENETICS AND BREEDING
SUBMITTED TO
DR.SAMITA SAINI
ASSOCIATE PROFESSOR
SUBMITTED BY
DR.RAMESH KUMAR PARMAR
MVSC SCHOLAR
TOPIC:MARKER (MAS) ASSISTED SELE
CTION

2. OVERVIEW
 Definition
 Marker Types
 Property Of Ideal Marker For MAS
 Positive And Negative Selectable Markers
 Gene Vs Marker
 Relation B/W Marker And Associated Gene
 Steps For MAS
 Factor For Success
 MAS Work Best For Traits
 High Throughput Genotyping Techniques
 Conclusion

3. What isMAS
• Marker assisted selection or marker aided selection (MAS) is
a process whereby a marker (morphological, biochemical
molecular etc.) is used for indirect selection of a genetic
determinant or determinants of a trait of interest (e.g.
productivity, disease resistance, abiotic stress tolerance
etc..).
• This process is used in plant and animal breeding.

4. MARKER TYPES
Positive and negative selectable marker
Positive selectable markers are selectable markers thatconfers
selective advantage to its host organism. An example would
be antibiotics resistance, which allows the host organism to
survive antibiotics selection.
Negative selectable markers are selectable markers that would
eliminate its host organism upon selection. An example would
be thymidine kinase, which would make the host sensitive to
ganciclovir selection.

5. Biological markers
• Different pathogen races or insect biotypes based on host
pathogen or host parasite interaction can be used as a
marker since the genetic constitution of an organism can
affect its susceptibility to pathogens or parasites.

6.  Animals are selected based on appearance.
 Disadvantage: lack of polymorphism
Morphological markers

7. Animal are selected on the basis of biochemical properties.
Eg.Hb,AMYLASE,BLOOD GROUPS ETC..
Disadvantage: Sex limited
Age dependent
Influenced by environment
It covers less than 10%of genome
Biochemical markers

8. Cytological markers
•The chromosomal banding produced by different stains; for example, G
banding.
•structural and numerical variations are identified.
• Structural- Deletions, Insertions etc.
• Numerical- Trisomy , Monosomy , Nullysomy
•Disadvantage : low polymorphism

9. DNA-based / molecular
 To avoid problems specific to morphological markers the DNA based
markers have been developed .
 A unique (DNA sequence ) occurring in proximity to the gene or locus
of intrest ,can be identified by a range of molecular techniques . Used
as molecular markers are RFLP SSR
 Three common technologies (microsatellites) and SNP .
ADVANTASES
 Highly polymorphic.
 Simple inheritance.
 Abundantly occur throughout the genome.
 Easy and fast to detect,
 Minimum pleiotropic effect.
 Detection is not dependent on the developmental stage of the organism.

10.  Easy recognition of all possible phenotypes(homo- and
heterozygote's) from all different alleles.
 Demonstrates measurable differences in expression between trait
types and/or gene of interest alleles, early in the development of
the organism.
 Low or null interaction among the markers allowing the use of
many at the same time in a segregating population.
 Abundant in number.
 Polymorphic.
Important Properties of Ideal Markers for MAS

11. Gene Vs Marker
 The gene of interest is directly related with production of
protein(s) that produce certain phenotypes whereas markers
not influence the trait of interest but are genetically linked .
 In many traits, genes are discovered and can be directly
assayed for their presence with a high level of confidence.
However, if a gene is not isolated, markers help is taken to
tag a gene of interest. In such case there may be some
inaccurate (even false) positive results due to recombination
between the marker of interest and gene (or QTL). A perfect
marker would elicit no false positiveresults.

12. Relationships b/w markers and respective
gene
•Three kinds of relationships between the markers
and respective genes could be distinguished :
(1)The molecular marker located within the gene of interest,
which is the most favourable situation for MAS and in this case,
it could be ideally referred to as gene-assisted selection. Such
markers are called as direct marker.
(2)The marker in linkage disequilibrium (LD) with the gene of
interest throughout the population. LD is the tendency of certain
combination of alleles to be inherited together. Population-wide
LD can be found when markers and genes of interest are
physically close to each other. Selection using these markers
can be called as LD-MAS.
(3)The marker in linkage equilibrium (LE) with the gene of interest
throughout the population, which is the most difficult and
challenging situation for applying MAS.

13. Cont
.
Direct markers are preferred for effective implementation of
marker-assisted selection, followed by LD and LE markers,
the latter requiring within-family analysis and selection.
Ease of application and potential for extra-genetic gain is
greatest for direct markers, followed by LD markers, but is
antagonistic to ease of detection, which is greatest for LE
markers.

14. Steps forMAS
 Generally the first step is to map the gene or quantitative trait
locus (QTL) of interest by using different techniques and then
use this information for marker assisted selection.
 Generally, the markers to be used should be close to gene of
interest (<5 recombination unit or cM) in order to ensure that
only minor fraction of the selected individuals will be
recombinants.
 Generally, not only a single marker but rather two markers are
used in order to reduce the chances of an error due to
homologous recombination. For example, if two flanking
markers are used at same time with an interval between them of
approximately 20cM, there is higher probability (99%) for
recovery of the target gene.

15. Three common technologies used as molecular markers are:
restriction fragment length polymorphisms, simple sequence
repeats, and single nucleotide polymorphisms.
Genetic variants often differ from each other by the sequence
of a single nucleotide so single nucleotide polymorphisms
SNPs (pronounced “snips”),
is commonly the basis of genotyping tests It is therefore
possible to genotype an animal using a DNA- based
genotyping test and select individuals carrying the preferred
genetic variant

16. Factorfor success ofMAS
MarkerA
QTL
5cM
In general , the success of MAS depends on folowing factor:-
(i)Availability of genetic map with an adequate number of
uniformly-spaced polymorphic markers to accurately locate
desired QTLs or major gene(s).
(ii) Close linkage between the QTL or a major
gene of interest and adjacent markers.
(iii) Ideally markers should be <5 cM from a gene or QTL
RELIABILITYFOR
SELECTION
Using marker A only:
1– rA =~95%
MarkerA
QTL
MarkerB
5cM 5cM
Using markers A and B:
A B
1- 2 r r =~99.5%

17. Cont…
Note- Using a pair of flanking markers can greatly
improve reliability but increases time and cost.
(iv)Adequate recombination between the markers and
rest of the genome.
(v)Ability to analyze a larger number of Animals in a
time and cost effective manner.

18. Fundament Advantages of MAS
1. Greater efficiency.
2. Accelerated line development in breeding programs.
For example, time and labour savings may arise from
the substitution of difficult or time-consuming field trials
(that need to be conducted at particular times of year
or at specific locations, or are technically complicated)
with DNA marker tests.
3 .Selection based on DNA markers may be more
reliable due to the influence of environmental factors
on field trials.

19. CONT....
4. Another benefit from using MAS is that the total number of lines that need
to be tested may be reduced considerably.
5. Since many lines can be discarded after MAS at an early generation, this
permits a more effective breeding design.
6. Greater efficiency of target trait selection may enable certain traits to be
fast-tracked, thus specific genotypes can be easily identified and
selected.

20. MAS work best fortraits
1. Low h2
2. Are difficult or expensive to measure. e.g. disease
resistance.
3. Can not be measured untill after selection has
occurred
e.g. Carcass data.
4 .Are currently not selected for due to lack of available
phenotypic data.e.g.(tenderness).

21. Traits most likely to benefit for MAS
(descending order ).
1. Disease resistance .
2. Carcass quality and palatability attributes.
3. Fertility and reproductive efficiency.
4. Maintenance requirements.
5. Carcass quantity and yields.
6. Milk production and maternal ability.
7. Growth performance.

22. High throughput genotyping techniques
Recently high-throughput genotyping techniques are developed
which allows marker aided screening of many genotypes. This
will help breeders in shifting traditional breeding to marker aided
selection. One of example of such automation is using DNA
isolation robots, capillary electrophoresis and pipetting robots.
 One of recent example
of capillary system is
Applied Bio systems
3130 Genetic Analyser.

23. CONCLUSIONS
In context of MAS, markers can be effectively utilized for two
basic purposes :-
tracing favourable allele(s) (dominant or recessive) across
generations.
Identifying the most suitable individual(s) among the
segregating progeny, based on allelic composition across a
part or the entire genome.
 It is important to combine DNA results (which look at single
genes) with other criteria, such as EPDs (which look at
numerous genes) and the animal’s actual phenotype for the
trait (if available), to ensure that selection is distributed over
all the genes that contribute towards the trait of interest.

24. CONT….
 Don't ignore animals that have good EPDs for a given trait and yet are not
carrying the favorable form of a gene for that trait.
 These animals arelikely to be a source of good alleles for the
many other genes that contribute towards that trait.
 Ideally the information from genetic tests should be integrated into a
genetic evaluation system that weighs all the information about an
animal. Combining information from both EPDs and genetic tests into
a selection decision will be superior to selection on either EPDs or
markers alone.

25. THANK YOU