What+the+shell+are+you+talking+about?+Intro

Introduction – Athena Wright Ballester*, Chandni Patel, Hannah Law, Taranya Paheerathan, Ceren Sonmez and Satwinder Kaur The primary objective of the trip was to investigate whether polymorphism is present within a population. Further more which elements or combinations, such as sampling variation, genetic drift or genetic drift and selection pressures are responsible for this. To successfully determine which of these aspects is influential we undertook a field study using snails as our test subject, more specifically the visible characteristics of the shell. Snails were chosen due to the ease of identifying their phenotype, mainly shown on their shells and ease of sampling, as they don’t have a wide range of migration distance over their life span. Specifically //Cepaea nemoralis// was the species studied and the phenotypes recorded were colour of shell, dead or alive, adult or subadults and number of bands. It has previously been stated in a journal entry entitled ‘Polymorphism in Cepaea: A problem with too many solutions?’ that “In many places there are differences in the microgeographical distribution of each of the four Cepaea which cannot easily be related to the environment. This suggests that the snails are detect-ing environmental discontinuities not apparent to us.” This is an element that we investigated in our study, where the dependent variable was the sampling sites; to include shrub land and grassland, three samples were taken for each insuring a level vertical gradient was maintained, moving across the horizontal plane. The use of the differing sampling sites was to consider what effects specific vegetation type and location may have on the selection of phenotypes within each sampling population. A sudden decrease in population size often results in a bottleneck effect, decreasing genetic diversity and as a result promoting genetic drift over natural selection. Bottlenecks within a population can also lead to psuedoreplication, this is due to the decrease in genetic pool size. Psuedoreplication takes place when there are many observations that aren’t statistically independent of each other, for example multiple observations on the same subjects when species are nested within the same habitat. The process of species invasion also effects selection within a population, as once established the species can potentially outcompete and displace original natives, affecting the flora and fauna of a habitat. It is often unlikely that the invasion is reversed. Other factors to consider include how genetic drift is present in all populations at different rates; whereby the smaller the population size the greater the effect of drift, and that this is an element of gene flow. Gene flow is the process in which alteration of the allele frequency in a population results from members of one gene pool mating with members of another gene pool. We hope to discuss from our findings whether in fact<range type="comment" id="468049316_9"> polymorphism has occurred i</range id="468049316_9">n our population and if so what elements have caused its presence.

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