Foreground and Background Selection using Marker Assisted Selection

1. Gene pyramiding. Foreground and
background selection using marker assisted
selection.

2. Gene pyramiding
Gene pyramiding or stacking can be defined as a process of
combining two or more genes from multiple parents to develop
elite lines and varieties.
Or
Pyramiding entails stacking multiple genes leading to the
simultaneous expression of more than one gene in a variety.
MAS based gene pyramiding could facilitate in pyramiding of
genes effectively into a single genetic background.

3. Introduction
 The development of molecular genetics and associated technology like MAS
has led to the emergence of a new field in plant breeding- Gene pyramiding.
 The term gene pyramiding is used in agricultural research to describe a
breeding approach to achieve pest control and higher crop yield.
 Gene pyramiding aims at the deviation of an ideal genotype that is
homologous for the favorable alleles at all n-loci. Molecular markers aid in
selecting the best plants with which to proceed.

4. Objectives of gene pyramiding
 Enhancing trait performance by combining two or more
complementary genes.
 Remedying deficits by introgression of genes from other sources.
 Increasing the durability of disease and/or disease resistance.
 Broadening the genetic basis of released cultivars.

5. Strategies for gene pyramiding
 Iterative procedure/sexual hybridization
 Re-transformation
 Co-transformation

6. Iterative procedures/sexual
hybridization
The plant harboring one or more transgenes is cross-
hybridized with another plant containing other
transgenes.
Development of a multi-stack hybrid occurs via iterative
hybridization.

7. Re-transformation
A plant harboring a transgene is
transformed with other transgenes.

8. Co-transformation
A plant is transformed with two or more
independent transgenes. The transgenes of
interest are in separate gene constructs and
deliver to the plant simultaneously.

9. The gene pyramiding scheme can be distinguished
into two parts.
The first part is called pedigree, which aims at
cumulating of all target genes in a single genotype
called the root genotype.
The second part is called the fixation step which
aims at fixing the target genes into a homozygous
state i.e. to derive the ideal genotype from the one
single genotype.

10. Basic assumptions of gene
pyramiding
 Locations of a series of genes of interest(target genes). Thus the
linkage relationship between them is known.
 Target genotype for these genes is defined prior to selection as the
genotype with favorable alleles at all loci of interest.
 The genotype of an individual can be identified by these genes or
markers linked to them.
 A collection of lines containing all target genes should be available.

11. What is a marker?
 All living organisms are made up of cells that are programmed by genetic
material called DNA. This molecule is made up of a long chain of nitrogen
containing bases(there are four different bases- adenine, guanine, cytosine,
thiamine).
 A molecular marker is a small region of DNA showing sequence
polymorphism in different individual within a species(or) among different
species.
 It is readily detected and whose inheritance can easily be monitored.
 A wide range of molecular techniques are now available to detect the
polymorphism at DNA level.

12. Marker assisted selection
According to Bertrand and Mackill, “the marker aided selection
(MAS) assumes that the target gene is identified and selected
based on the closely linked markers”.
A successful MAS requires that a gene be mapped and closely
linked to a marker, otherwise which is very difficult to examine
or evaluate by conventional approaches.

13. Why marker assisted selection
 Selection at seedling stage possible.
 Selection of traits with low heritability.
 Distinguishing homozygotes from heterozygotes.
 Pyramiding of resistance genes.
 Selection of recessive genes etc.

14. Why marker assisted
pyramiding
 Markers provide a more effective option to control linkage drag and
make the use of genes contained in unadapted resources easier.
 Pyramiding is possible through conventional breeding but is
extremely difficult or impossible at early generations.
 DNA markers may facilitate selection because DNA marker assays
are non-destructive and markers for multiple specific genes can be
tested using a single DNA sample without phenotyping.

15. Marker assisted breeding for biotic resistance in rice

16. Conclusion
 Gene pyramiding is an important strategy for
germplasm improvement.
 Molecular marker genotyping can facilitate the gene
pyramiding process by reducing the number of
generations that breeders must evaluate to ensure they
have the desired gene combinations.

17. THANK
YOU

18. Reference:
 http://www.isaaa.org/resources/publications/pocket/42
 Gene pyramiding using molecular markers – Francis et al,
2012
 http://agbiosafety.unl.edu/education/backcross.htm
Submitted to:
DR. KOUSIK KUMAR
PANIGRAHI(Asst. Prof. Plant
Breeding and Genetics)
Submitted by:
Jagatjyoti Pattnaik
Adm.no: 52HO/16