Marker assissted selection
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MOLECULAR MARKERS AND MARKER ASSISTED SELECTION
SHAKIL BHATP.G. SCHOLAR
ANIMAL BIOTECHNOLOGY
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Introduction
In developed countries animal breeding is based on quantitative genetics
Nicolas,(1996)
Quantitative genetics is multifactorial, influenced both by gene and environmental factors and their interaction
(Beuzen et al., 2000)
Improvement of livestock focuses on the selective breeding of
individuals with superior phenotypes Williams,(2005)MAS is a powerful tool in animal breeding, improves the whole range of desirable traits
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MARKERS
MORPHOLOGICAL
CHROMOSOMAL
BIOCHEMICAL
GENETIC
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MORPHOLOGICAL MARKERS
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BIOCHEMICAL MARKERS
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CHROMOSOMAL MARKERS
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Molecular markers
Molecular marker are specific fragments of DNA that can be identified within the whole genome
They are used to 'flag' the position of a particular gene
Molecular markers are used in molecular biology to identify a particular sequence of DNA
(Chauhan and Rajiv, 2010)
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Features of Molecular Markers
Characteristics:Co-dominant expression
Early onset of phenotypic expression
High polymorphism Random distribution throughout
the genome Assay can be automated
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Hybridization- based DNA markers
RFLP, oligonucleotide fingerprinting
PCR based DNA markers
RAPD, AFLP, SSR
Sequencing based DNA markers and DNA Chip
SNP
Classes of Molecular Markers
Vogel et al.,(1998)
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Restriction Fragment Length Polymorphism (RFLP) Principles
RFLP analysis is a standard, well-tested procedure for estimation of genetic diversity Tanksley, (1993)
RFLP analysis is based on the ability of restriction enzymes to cleave DNA at specific target nucleotide sequences
Fairbanks, (1995)
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• Simple sequence repeats are present in the genomes of all eukaryotes and consists of several to over a hundred repeats of a 1-4 nucleotide motif.
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SNP
• The most common genetic polymorphism
• Distribute throughout genome with high density
• More stable and easy to assay
• Facilitates large scale genetic association studies as genetic markers.
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MARKER ASSISTED SELECTION
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THEORY AND PRACTICE
ADVANTAGES
MAS vs PHENOTYPIC SELECTION
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The process of using the results of DNA-marker testing to predict the genetic merit of the animal being tested and assist in the selection of individuals to become parents in the next generation.
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• Marker assisted selection (MAS) is an indirect selection process where a trait of interest is selected not based on the outward appearance of the trait itself but on a genetic marker near the trait (gene) on the DNA.
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• MAS - Use of information from genetic markers to help make selection decisions of animals for genetic Improvement.
• This is done in a manner that exploits both known major genes and all unknown genes.
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CONVENTIONAL BREEDING
P1 P2
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MARKER-ASSISTED BREEDING
P1 X P2
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MAXIMIZE GENETIC GAIN
TO REDUCE POPULATION
SIZE FOR TRAITS
LEVEL OF RECOMBINATION
BETWEEN MARKER AND QTL
Combined approaches
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ADVANTAGES
TIME COST RECESSIVE GENES
LOW HERTIBILITYSEASONAL
CONSIDERATIONSGEOGRAPHICAL
CONSIDERATIONS
GENE STACKING EARLY DETECTION MULTIPLE GENES
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QTL DETECTION
GENE MAPPING
MARKER GENOTYPING
GENETIC EVALUATION
REQUIREMENTS
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Potential benefits from MAS are greatest for traits that
Have low heritability
Are difficult or expensive to measure (disease resistance)
Are currently not selected for as they are not routinely measured (tenderness)
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•Time consuming
•Difficult
•Costly
•Performed off season
•Gene pyramiding
•Early stages of development
•Several selections simultaneously
•Low heritability traits
MAS Vs. PS
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MAS in selection programming
BETWEEN BREED
SELECTION
INTROGRESSION
IMPROVEMENT OF SYNTHETIC LINES
WITHIN BREED
SELECTION
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CURRENT STATUS OF MAS
OBSTACLES
CHALLENGES
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Low impact of MAS
Resources not availableMarkers may not be cost-effectiveQTL mappingQTL effects may depend on genetic background or be influenced by environmental conditionsPoor integration of molecular genetic and conventional breeding
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Cost - a major obstacle
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Future challenges
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