BACKGROUND
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"From Markers to MAS"
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Gel electrophoresis & analysis
Every lane of black markers is information from one plant each, and the blue lane is the set of standard sized DNA fragments used to identify the PCR DNA. Using these markers, it is possible to see which plants have desirable traits such as disease resistance. The connection between markers and traits are based on genetic studies and QTL maps that have associated a specific marker with a specific trait. Based on DNA fragment size, the plants with the genes needed to resist a disease are found while the plants are still only seedlings.
“In this way ... breeding populations can be biased towards plants with desirable characteristics” (Citation 2)
After PCR takes place, the DNA samples are dyed and injected into polyacrylamide gel and gel electrophoresis takes place.
HOW IT WORKS
The sets of 96 tissue samples are then agitated, then subsequently inserted into a centrifuge and spun to decrease the foam from the agitation. The samples are then heated to release DNA. Chloroform is added, then mixed. They are put into the centrifuge again to separate DNA and water from proteins and lipids.
Obtain leaf tissue from a crop (ex. young tomato shoots) to be used for DNA extraction, and insert them into test tubes. MAS. is performed with usually 96 individual tissues, due to its efficiency. Metal balls are also added to stabilize weight and make it easier to disperse plant tissue. Lastly, detergent based extraction buffer is added.
Collection and setup
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Obtaining DNA samples
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PCR
The DNA is removed from the water and added to new test tubes. Alcohol is added then the samples are centrifuged again and then dried so only DNA is left with residual alcohol. The DNA is then added to a solution, which is then used for Polymerase Chain Reaction.
The resistant crops are then planted to the fields to see physically how well suited they are to the environment, their adaptability, and their performance.
As more genetic studies are done, more information of markers are released, allowing a wider pool of markers to screen for and choose from to choose the best plants. (Citation 2)
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Field testing & application
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Uses a species' own genes, not another species'
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Fewer ethical issues associated with MAS
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Due to testing taking place in the seedling stage, MAS is much quicker (Early Selection)
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Uses analysis of the genotype, not the phenotype (Citation 4)
Marker Assisted Selection Advantages over GMO
TERMINOLOGY
Codominance: A gene that has no dominant or recessive trait, the phenotype is expressed no matter what. In MAS, codominance in a marker is preferred because it is more informative than dominant marker. (Citation 15)
DNA Primers: Used in PCR among other things, DNA primers are nucleotide strands attached to the ends of a DNA strand (Citation 16)
Genetic Map: A map that shows the general area in which genetic loci lie on a chromosome based on the frequency in which the loci are inherited together. (Citation 44)
Linked Map: A map that shows the general area in which genes lie on a chromosome. Linked genes are genes that are inherited together, and therefore close to each other on the chromosome. (Citation 44)
Locus: The location of which a certain gene is located on a chromosome. (Citation 9)
Polymorphism: An observable difference in a gene or marker found within organisms. (Citation 44)
Quantitative Trait Locus Analysis(QTL): A locus is the exact area where a gene is found in a chromosome. Quantitative Trait Locus Analysis is used to map the connections between molecular markers and DNA bases such as SNPs and SSRs. Subsequently, a QTL map serves to help MAS operate and detect which traits are useful and where they are on the chromosome. (Citation 8, 9, 3)
Marker Assisted Selection, or MAS for short, is the use of molecular markers to select desired traits within plants, animals, or organisms. Often referred to as the child of “traditional genetics and molecular biology”, this process has rapidly gained popularity and acceptance over genetically modified crops in the past few years. MAS is conducted through a DNA test using a crop, its DNA, PCR, and gel electrophoresis. Using gel electrophoresis, the DNA is sorted to display traits linked through markers. The crops with favorable traits, such as resistance to disease, are then selected to see how they do in the real world. Taking the “cream of the crop” from both the results shown in DNA testing and the actual performance of the crop selected from the testing, these become the parents of the next generation of crops, which are then subjected to MAS again. MAS can be seen as a faster, better version of traditional selective breeding, due to DNA marker assistance. In addition, it also doesn’t use the genes from another organism; everything comes from the original organism and its desirable traits.
For a detailed explanation of the various types of markers, click here:
MAS
GMO
Here are additional video supplements on the basics and background of MAS.