Genotype-By-Environment Interaction (VG X E) wth Examples
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The document discusses genotype-by-environment interactions and their role in phenotypic variation within populations. It highlights two forms of interactions, the effects of environmental changes on phenotype, and presents examples from plant species such as Achillea millefolium, demonstrating local adaptation and the influence of climatic factors. Additionally, it emphasizes the growing ability to analyze genetic differences to further understand gene-environment interactions.
Genotype-By-Environment Interaction (VG X E) wth Examples
- 1. Population Genetics 1 Genotype-By-Environment Interaction (VG X E) Introduction Phenotypic variation can be caused by the combination of genotypes and environments in a population. Genotypes are all equally sensitive to their environments, meaning that a change of environment would impact the phenotype of all genotypes to the same extent. In fact, genotypes very often have different degrees of sensitivity to environmental conditions. This cause of phenotypic variance is called genotype by- environment interaction and is symbolized by VG x E. This adds another term to the expression for the independent causes of total phenotypic variation in a population Ve = VG + VE + VG xE Two forms of interaction exist 1. In one form of genotype-by-environment interaction, genotypes are extremely sensitive to changes in the environment such that the total phenotypic variance changes markedly between two or more environments. 2. In another form of genotype-by-environment interaction, genotypes change phenotypic rank in different environments. For example, genotype AA has a larger phenotypic value than genotype Aa in environment one but in environment two the order is reversed with genotype Aa having the larger phenotypic value. Definition The contribution to total phenotypic variation caused by genotypes that vary in their sensitivity to different environments and is also known as phenotypic plasticity.
- 2. Population Genetics 2 Examples Some gene–environment interactions can be identified without any molecular analysis; one example is the much stronger effect of sunlight exposure on skin cancer risk in fair-skinned humans than in individuals with darker skin 2. Others can be observed as a reproducible effect of an environmental exposure on a susceptible individual for example, the flushing response seen after alcohol ingestion in individuals with low activity polymorphisms in the aldehyde dehydrogenase gene 3. However, our rapidly expanding ability, particularly after the completion of the Human Genome Project, to define genetic differences at the DNA-sequence level is opening up a vast new terrain in the search for gene–environment interactions 1. Genotype-By Environment Interaction In Achillea Millefoliu. Seeds were collected, germinated, and grown (up to 60 individuals/population) in a common garden at Stanford for 81 natural populations of Achillea from western North America, Scandinavia , and the Aleutian Islands . Populations were characterized (growth, reproduction) and 30 individuals from 14 selected populations were cloned and used for transplanting at the Stanford, Mather, and Timberline field stations. Once each individual plant were cloned, replicates were transplanted to each station and morphological and physiological characters were recorded (e.g., height, number of stems, time of flowering, and survival, among others) over a three year period. The results of the transplant experiment revealed, as expected, variability in morphological and physiological characters among populations. Survival and reproduction were markedly reduced for some transplanted populations. In contrast, natives did very well in their own environment, supporting their conclusion of local adaptation by selection.
- 3. Population Genetics 3 CKH (Work of Clausen, Keck, and Hiesey) differentiated a total of eleven climatic races or ecotypes of Achillea along the 200-mile transect across central California. There was genetic differentiation in morphology, and especially for physiological traits, although the selective importance of many characters could not be guessed at. Figure 1 illustrates the evidence of strong selection (i.e., stem lengths of 0 at Timberline), as well as the environment dependent expression of phenotypic variation among populations, with substantially more differentiation evident at Stanford. Figure 1. Reaction norms for stem length (the longest stem) of clones of various different populations of Achillea at the three transplant stations along transect from the coast to the Sierra Nevada in Central. Some clones did not survive at Timberline.
- 4. Population Genetics 4 To assess the factors that interact with the genotypes in the field and produce the diversity of reaction norms, CKH performed controlled experiments in which they varied light and day/night temperature. Generally, populations from the coast to Mather performed better in cool days (17C) and mild nights (13C) and, in contrast, populations from high altitude and from the Great Basin performed better in warm days (26C) and nights (17C). These differences in growth optima reflect the climatic differences between the habitats of the populations. These greenhouse experiments reinforced the important role of climatic factors in shaping physiological characters important in plant survival and reproduction, such as the presence and length of the dormant period, growth rate, onset of flowering, and frost resistance. 2. Genes Contributing To Character Expression In Potentilla Glandulosa Work Of CKH
- 5. Population Genetics 5 3. Other Examples
- 6. Population Genetics 6 References Hunter, David J. "Gene–environment interactions in human diseases."Nature Reviews Genetics 6.4 (2005): 287-298. Núñez-Farfán, J., and C. D. Schlichting. "Evolution in changing environments: the" synthetic" work of Clausen, Keck, and Hiesey." Quarterly Review of Biology (2001): 433- 457. Clausen, Jens, David D. Keck, and William M. HIESEY. "Experimental studies on the nature of species. III. Environresponses of climatic races of Achillea." Experimental studies on the nature of species. III. Environresponses of climatic races of Achillea. Publ. 581 (1948). Hamilton, M. (2009). Population genetics. Chichester, UK: Wiley-Blackwell. Acknowledgments 1. Dr. Abdul Rehman Khan, Assistant Professor, Department of Environmental Sciences, CIIT, Abbottabad 2. Dr. Sabaz Ali Khan, Assistant Professor, Department of Environmental Sciences, CIIT, Abbottabad