The process of developing new crop
varieties requires many steps and can take almost 25 years. Now, however,
applications of biotechnology have considerably shortened the time it takes to
bring them to market. It currently takes 7-10 years for new crop varieties to be
developed. One of the tools, which makes it easier and faster for scientists to
select plant traits is called marker-assisted selection (MAS).
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Molecular shortcut:
The differences which distinguish one plant from another are encoded in the plant’s genetic material, the DNA. The DNA occurs in pairs of chromosomes (strands of genetic material), one coming from each parent. The genes, which control the plant’s characteristics, are specific segments of each chromosome. All of the plant’s genes together make up its genome.
Some traits, like flower color, may be controlled by only one gene. Other more complex characteristics, however, like crop yield or starch content,may be influenced by many genes. Traditionally, plant breeders have selected plants based on their visible or measurable traits, called the phenotype. But, this process can be difficult, slow, influenced by the environment, and costly - not only in the development itself, but also for the economy, as farmers suffer crop losses.
As a shortcut, plant breeders now use marker-assisted selection. To help identify specific genes, scientists use what are called molecular markers. The markers are a string or sequence of nucleic acid which makes up a segment of DNA. The markers are located near the DNA sequence of the desired gene. Since the markers and the genes are close together on the same chromosome, they tend to stay together as each generation of plants is produced. This is called genetic linkage. This linkage helps scientists to predict whether a plant will have a desired gene. If researchers can find the marker for the gene, it means the gene itself is present. As scientists learn where each of the markers occurs on a chromosome, and how close it is to a specific gene, they can create a map of the markers and genes on specific chromosomes. These genetic linkage maps show the location of markers and genes, and show their distance from other known genes. Scientists can produce detailed maps in only one generation of plant breeding.
It should be noted, however, that molecular breeding through marker assisted selection is somewhat limited in scope compared to genetic engineering or modification because:
1) it only works for traits already present in a crop;
2) it cannot be used effectively to breed crops which have long generation time (e.g. citrus); and
3) it cannot be used effectively with crops which are clonally propagated because they are sterile or
do not breed true (this includes many staples such as yams, bananas, plantain, sweet potato, and cassava).
