Role of Genetic Variation in Determining a Quantitative Trait

Question: Discuss about theRole of Genetic Variation in Determining a Quantitative Trait. Answer: Introduction Background Information The population can be genetically defined by documenting the genotypic and allelic frequencies, which can be calculated using the Hardy-Weinberg Equilibrium equations. This phenomenon was developed by Gregor Mendel who contributed much to the development of genetics by defining how traits were inherited from one population to another (Charlesworth, 2015). According to Gregor, who said to be the father of genetics, alteration of the genetic makeup of an individual or a population would lead to evolution. Changes in allelic frequencies would lead to deformation of the possible genotypes that can be produced in the next generation. The changes in the frequency of alleles can be facilitation by factors such as genetic drift, mutation, gene flow, non-random mating and selection (Charlesworth, 2015). Genetic variation changes the possible combination of alleles hence affecting their phenotypic effects on the offspring. For instance, a change on a recessive allele by mutation to become domi nant would lead to a heterozygous or homozygous dominant offspring (Cavalli-Sforza, 1986). Genotypic Influencers The next generation is always determined by the type of mating that happens in the current population. In small populations, loss of reproduction or death can lead to genetic drift that causes loss of a particular trait that could be passed to the next generation. A phenotypic trait is always an interaction between the environment and genotypic composition (Slankster, Chase, Jones, Wendell, 2012). For instance, individuals living in an environment that are exposed to high temperatures will lead to changes in their genome making them better adapted to the environment. The changes contribute to producing offspring individuals who would survive in such environmental conditions. Therefore, the genetic changes are aimed at enhancing a better future for a particular population (Reed Frankham, 2001). Phenotype and Environment Phenotypic plasticity allows genotypic changes to enhance the adaptability of individuals as a result of environmental changes. The different environmental factors might lead to modifications on the physiology, behaviours and morphology of individuals. The main importance of plasticity if to make a population that has genotypic combinations that can survive certain environmental factors of interest. Lack of phenotypic plasticity to some individuals in the population might lead to natural selection, where those who are able to adapt quickly would replace the others. In this case, evolution will be experienced and the next generation will have genetic combinations that are different compared to those who were unable to withstand the environmental conditions. The plasticity of a population usually interacts with the environment to generate a genetic combination that would adapt to the factors in question. The difference between populations can be determined by their distinction on their environments. Elasticity can be lost from the genotype when there is no selection in the environment to create a better-adapted population (Goudet, 2005). Therefore, populations which experience environmental changes do not lose their plasticity and they have better chances of surviving if ever there is an environmental change. The distribution of alleles in the chromosome determine the genotype and any changes dues to plasticity do not change the genotypic arrangement to the population due to environmental factors. Otherwise, plasticity increases the probability that the population will have persistent characteristics towards the environmental factors (Stearns, 1989). Brassica Rapa and Environment Brassica rapa was grown under three situations where three genotypes were grown under distinct conditions. This kind of research was aimed at understanding how the genotypes and the environmental factors would affect the phenotypic appearances of the plant. These environmental conditions included anthocyanin and shortwave ultraviolet (UVB, 280-325 nm) (Klaper, Frankel Berenbaum, 1996). The variables for the study included plant genotype and phenotypic characteristics that included height, leaf length and flower count. Purpose of the Study Exposing this kind of environmental factors was aimed at stressing the plant to observe how it would adapt to the new changes. Its plasticity would enhance the chances of surviving in the extreme conditions and being able to reproduce. After the study was completed in 41 days, differing observations were identified towards how Brassica rapa adapted to the environment (Klaper, Frankel Berenbaum, 1996). The presence of UVB leads to the reduction of plant height and leaf length to enable it to reduce the rate of photosynthesis. On the other case, reduced anthocyanin levels led to the reduction of flower count by half of those with normal and extended levels. This research study proved that other than pigmentation effect of the UV light, plants can adapt for better survival in the environment. Hypothesis The possible hypothesis that could be tested in the study include: - Null hypothesis: There is no effect on the height of the Brassica rapa plant Alternative hypothesis: The short wave ultraviolet rays affects the height of the plant Null hypothesis: There is no effect of shortwave ultraviolet to the Brassica rapa leaf sizes Alternative hypothesis: There are effects of shortwave ultraviolet to the Brassica rapa leaf sizes Null hypothesis: There is reduced levels of anthocyanin to the Brassica rapa plant Alternative Hypothesis: The levels of anthocyanin increases in the plant References Cavalli-Sforza, L. (1986). Population genetics. Trends in Genetics, 2, 220. Doi: 10.1016/0168-9525(86)90234-9 Charlesworth, B. (2015). What Use Is Population Genetics? Genetics, 200(3), 667-669. https://dx.doi.org/10.1534/genetics.115.178426 Goudet, J. (2005). The Effects of Dominance, Regular Inbreeding and Sampling Design on QST, an Estimator of Population Differentiation for Quantitative Traits. Genetics, 172(2), 1337-1347. doi:10.1534/genetics.105.050583 Klaper, R., Frankel, S., Berenbaum, M. (1996). Anthocyanin Content and UVB Sensitivity in Brassica rapa. Photochemistry and Photobiology, 63(6), 811-813. doi:10.1111/j.1751-1097.1996.tb09635.x Reed, D. Frankham, R. (2001). How Closely Correlated are Molecular and Quantitative Measures of Genetic Variation? A Meta-Analysis. Evolution, 55(6), 1095-1103. doi:10.1111/j.0014-3820.2001.tb00629.x Slankster, E., Chase, J., Jones, L., Wendell, D. (2012). DNA-Based Genetic Markers for Rapid Cycling Brassica Rapa (Fast Plants Type) Designed for the Teaching Laboratory. Frontiers in Plant Science, 3. https://dx.doi.org/10.3389/fpls.2012.00118 Stearns, S. (1989). The Evolutionary Significance of Phenotypic Plasticity. Bioscience, 39(7), 436-445. Doi: 10.2307/1311135