Group+3+Intro

Group 3 - Mohamed El-kholy*, Abdul Ahad, Tugrul Bardak, Sercan Kobazoglu, Clio Hall

Introduction

T he genus // Cepaea // is made up of air breathing land snails. In particular we are looking at the species // Cepaea // // nemoralis // (C. Nem). C. Nem is characterised by a large globular shell and a brown lip. It has varying banding patterns and colorations on its shell, I.e. it exhibits polymorphism. Polymorphism is where organisms with the same genotype exhibit varying phenotypes. The studies on C. Nem has lead to various conclusions being drawn about the presence of polymorphism. Factors such as mutation, genetic drift, selection and gene flow have all been attributed to causing polymorphism.

In Jones, Leith, Rawlings (1977) study the presence of polymorphism in the genus //Cepaea// was researched. They studied the patterns of gene frequency distribution and evolution of the shell polymorphism with factors such as visual selection, climatic selection, frequency dependent selection, density dependent selection and random processes being analysed for their involvement in the presence of polymorphism. The study found that the presence of polymorphism was a complex combination of all the aforementioned factors and concluded that it is not possible to come up with a set of general rules to explain the presence of polymorphism and that unique explanations may be needed for each //Cepaea// population.

We shall be attempting to understand whether genetic drift, selection or a combination of both are the driving factors behind C. Nem polymorphism. The site we are carrying out our study at (Monks riseborough) is a field with multiple different environmental habitats. In our investigation we are looking at selection and genetic drift as the potential prime factors behind polymorphism. We want to look at whether there is a significant difference between the frequencies of the phenotypes in the different habitats that we analyse.

In our investigation we shall be studying the presence of polymorphism in C. Nem. We chose to use C. Nem as our model organism of choice as their mobility is limited and it is relatively easy to analyse their phenotypes. We are observing different phenotypes by looking at the different banding patterns and colourations present on the C. Nem. The different observable phenotypes are red, brown and pink with banding patterns varying from no bands upto five bands.

Our experimental design revolves around us analysing the frequencies of phenotypes in the six sites within Monks Riseborough that we chose. The presence of phenotypes along with the mortality of snails and particular population will be taken into account when looking at phenotypic frequencies and the potential factors driving these frequencies.

We chose to ignore mutation as a possible explanation for polymorphism as the frequency of the varying phenotypes is significantly higher than would be expected. Our experimental design allows us to analyse the potential effects of selection or genetic drift in relation to polymorphism. We aim to have gathered data on the six populations and use it to come to a conclusion on whether there is a significant difference in phenotypic frequencies between populations and whether this is due to genetic drift, selection, a combination of both or entirely different factors.