Genetic mutation can be defined as alterations that occur to the nucleotide sequence of DNA or RNA material of a plant or organism. Mutations can occur as result of errors during cell division or it can be caused exposure to a variety of mutagens. Somatic mutations in plants can be transmitted to descendants either through sexual or asexual reproduction. Mutations are known to create a variation in the gene pool. Unfavorable mutations are reduced by natural selection while favorable mutations are accumulated for adaptive evolution. Mutations not only alter the expression of genes but also a change in the gene product.
Alterations may sometime be visible like change of a fruit shape, fruit color or it may change a physiological process. It is generally accepted that mutation is a very weak force in changing allele frequencies but a strong force in the introduction of new alleles. Mutation also creates new genotypes. Variation caused by mutation is very important in evolution. Natural selection in plant systems is a directional process that increases the frequencies of genes acquired by mutation. Plant resistance alleles on the other hand are increased through co evolution.
This paper tries to outline genetic mutation in plants with special emphasis on the variation of tomato (Solanum lycopersicum) size. Discussion Variations of tomato size between those that we buy in the grocery and those in the wild can be associated with the mutation caused in the fasciated gene. The expression of the gene puts a lid on the growth of the tomato by limiting the compartmentalization to a certain number. A couple of mutations occurred in the course of evolution causing the presence of the tomatoes we see today. The tomatoes are more than one thousand times bigger than the ones that are found in the wild.
Apart from the compartmentalization the genes also control the number of these seed bearing compartments, an increase of the seed bearing compartments lead to the development of a bigger fruit. When mutation occurs the gene fasciated when expressed lead to an increase in the number of compartments, scientists have been able to use this knowledge and hence breed bigger varieties of tomatoes. In addition to the increase in size cultivators have been able to improve the shape, flavor, increase shelf life and improve on constituent nutrient composition of tomatoes.
However to conclusively isolate and study these traits has been difficult because many genes are involved in the action. These genes are located together in close proximity. In the chromosome there are regions called loci. Regions located together and express a single trait as in this case, are referred to as quantitative trait loci (QTLs) (http://www. sciam. com/podcast/episode. cfm? id=02E1BC1E-CED4-A1E5-853CE5A1D1D3AA4C) With genome sequencing and other genomic tools, these regions can be mapped and subjected to cloning with relative efficiency. Using these maps other related genes can be identified from other plant species.
It is this knowledge that is used in the improvement of tomato species. Tomato (Solanum lycopersicum) belong to the family Solanaceae. A project called Tomato Genome Sequencing has been used to clone and also characterize the gene and QTL. QTL is used in the expression of fruit size. QTL, fw2. 2 was the first gene cloned in the plant. When cloning and sequencing was done it was revealed that the wild type protein coded for the repressor. When the gene used as a control was mutated the expression of the repressor gene was not there or it was very little.
The resultant effect is increased cell division and bigger fruit development. However it is important to note that, fw2. 2 and other genes associated with fruit development are not the sole determinants in fruit size. There are two other loci: the 2-4 locules and fasciated (fas) gene also indirectly affect the carpel numbers. Notably, the locule number has the ability to increase the fruit size by as much as 50%. The protein YABBY is encoded by the fas gene. This protein that acts like a transcription factor controls the transcription of both DNA and RNA during the first step in gene expression.
The mutation basically consisted of the insertion of an intron within the sequence of the coding protein. Introns are functionally important. They are also structurally important in the locus. They reduce the expression of the fasciated gene (http://www. npr. org/templates/story/story. php? storyId=90373214) More developments are now targeting the process of tomato ripening, tasting and nutrition. A set of genes called MADS-box gene are necessary in ripening and sepal development. These genes can now be manipulated to help increase the shelf life of tomatoes.
The ripening process can now be slowed to allow for transportation to supermarkets around the world. This long shelf life had led to complaints of blandness and researchers are now working on a major genetic modification that would allow the tomatoes in the shelves to be a lot more tastier. A hairy vetch is currently being used to activate some metabolic pathways in tomatoes making the fruits much tastier and nutritious. Hairy vetch inserts ySAMdc gene in the biotechnological tomatoes. The gene creates high polyamine levels signaling the production of more phytonutrients. Genetically modified tomatoes can now produce geranol.
Geranol is a role smelling compound usually found in flowers and fruits. This has again opened a new avenue in research where breeders can replace or restore the taste or aroma of fruits or vegetables. Conclusion Modern biotechnological techniques that involve recombinant DNA techniques, mutagenesis and tissue culture techniques have been used to deliberately alter genes and reintroduce them into host plant to test the expression of the altered genes. The techniques have been beneficial as they have been used most importantly to provide food security both in developed and developing countries.
The potential of scientific abuse of these techniques requires major regulatory frameworks especially in developing countries that do not have the research or technological capacity to test the possible health hazards or long term negative health influences of consumption of the products of genetically modified genes. Improvements in farming using induced genetic mutation procedures as the key scientific principle leads to the production of visually attractive and aesthetic fruits. However, research has proved that the fruits contain a high level of antioxidants.
The increase of antioxidant capacity despite their benefits is a source of concern and it remains to be established what causes this increase together with health impacts. Tomato moneymaker breed have been engineered to produce ribonucleic acid molecules that cause an inhibition of the disease causing genes. All plants that had undergone transformation remained tumor free even after they had been subjected to bacterial infection. The introduction of the resistance genes is beneficial for plant breeding and tests are still underway to analyze if the results can be replicated in other plant species.
Works Cited
American Society of Plant Biologists. “Evolution of Fruit Size in Tomato. ” Science Daily 1 July 2008. 20 September 2008. Accessed on 20 September 2008 from: <http://www. sciencedaily. com/releases/2008/06/080628065632. htm>. Karen Hopkins: Scientists Catch Up to Mutant Tomatoes <http://www. sciam. com/podcast/episode. cfm? id=02E1BC1E-CED4-A1E5-853CE5A1D1D3AA4C> Mammoth Tomatoes Arose from Genetic Mutation. http://www. npr. org/templates/story/story. php? storyId=90373214 Science Daily (Apr. 12, 2002): Tomato Catch-Up: Discovery Of Ripening Gene Could Make Store-Bought Tomatoes As Tasty As Homegrown. <sciencedaily. com>