Elin+intro

Elin Grigorian, 100307311 __Introduction__ Polymorphism is the existence of __many allelic forms of DNA sequences at certain loci[more than one at a locus]__ within a population. //Cepaea nemoralis//, otherwise known as the grove snail is one of the most common species of land snail in Europe, they are highly polymorphic in their background shell colouring and banding patterns. Their shell colours can range from light yellow to dark brown, and their bands can vary from zero to six bands. As this species displays clearly observable phenotypic differences, it makes them a suitable choice for study as they can easily be __identified in [classified into]__ genotypic categories. The aim of this experiment is to observe patterns in changes of allele frequencies of sampled //C. nemoralis// populations from different locations and to determine whether or not these changes are just due to chance or as a result of evolutionary processes such as natural selection. Another key reason for the selection of the species //C. nemoralis// in this study is that their individuals are generally slow moving and their populations tend not to travel over long distances, this therefore allows a large sample size to be made possible on a small scale. Furthermore this investigation is intended to help our understanding of the evolutionary principles affecting such polymorphism in snails; this knowledge can also be applied to other species’ such as humans where although polymorphic traits are much less distinct and harder to study, the same evolutionary processes such as drift, flow and selection can still have effects. Natural selection, gene flow and genetic drift are the main evolutionary processes that can result in polymorphism. In the 1950’s Cain and Sheppard considered that //C. nemoralis’// polymorphism was to some extent a result from selective predation acting on their phenotypes rather than on specific genotypes. More recent studies (M. Ozgo, 2005) have also shown selection may have an effect of the polymorphism of C. nemoralis snails as the colonies of //C. nemoralis// in open habitats have been found to be significantly less polymorphic than colonies in shaded habitats, implying that in more extreme climatic conditions, selection can act against certain genotypes. Although these results depend on different gene pools and are at different locations, they lead me to hypothesise that at different altitude level samples of C. nemoralis should show differences in their phenotypes. As altitude can affect a habitat in many ways, such as determine the types of predators able to live or predate in the habitat, or the types of prey able to survive. In this study we aim to investigate the prediction of polymorphism due to selection acting on //C. nemoralis// by analysing results from over 300 samples taken from both high and low altitude habitats. The sampling system of this investigation is to be carried out by a group of six individuals arranged equally apart from each other using a line transect to record the number of snails from a high region of grassland to a lower region. This will be repeated 3 times in different high/low altitudes. One of the individuals will be in charge of recording the data and the collectors are to bring their results to this person each time to discuss the appropriate category to classify the shells phenotype into. If our hypothesis is to be correct the results should help justify that individuals collected from the same habitat, for example all the high altitude samples, will have similar phenotypic traits. Where as individuals from different habitats, for example snails from high and low samples, will differ in genotype, and therefore will be more phenotypically different to each other. The conclusion of this investigation aims to determine whether natural selection is acting on the polymorphism of //C. nemoralis//. The results of this study will be statistically examined using the chi squared method of analysis. If the sampled data shows a difference between high and low habitats which is greater than a probability rate of 5% then the null hypothesis of our study should not be rejected. However, if it is found that there is no such significant correlation between phenotype distribution and habitat. The main reason for this is most likely to be because of gene flow or genetic drift. Although it can still be a possibility that natural selection is acting on the //C. nemoralis// species, except it could be that the altitude difference in this study may not be enough to act upon the phenotypes. Also there may not have been sufficient time for the generations of //C. nemoralis// populations to evolve and lead to a significant division of phenotypes which show clear signs of selection between them. Additionally there could also be non- visual selection acting on the species that we have not included in our study.

__References__ =Cain and Shepard (1954), Variation with habitat in //Cepaea nemoralis //. Journal of Molluscan Studies (2008) Volume: 74, Issue: 3, Pages: 239 - 243 = =M. Ozgo, (2005), //Cepaea nemoralis// //(L.) in south-eastern Poland: association of morph frequencies with habitat.// Journal of Molluscan Studies (2005) Volume: 71, Issue: 2 , <span class="info" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">Pages: <span class="pages" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">93-103 = = =