lumachine


 * __Lumachine __**
 * __Group members: __**

- Martha Foiani - Karina Kaur - Nisha Patel - Sophia Walsh - Madeleine Berry

On this field trip we will be studying the snail //Cepaea nemoralis. //We will be using the snail //Cepaea nemoralis //to observe polymorphism of shell colour and banding patterns formed on the shell. In biology, polymorphism is defined as the presence of multiple alleles in populations of a species at a specific gene locus, which may or may not have a phenotypic outcome. An example is the different types of blood in humans. Polymorphisms can arise from various reasons i.e. Mutation, genetic drift , gene flow and natural selection. In our study we will be looking at how these processes can affect a polymorphic population.

[1]Snails polymorphsim In this picture we see two phenotypical variations of the same species of snails.

We use snails as our subject because they show a clear phenotypical difference in pattern and shell colour between individuals of the same species and they don’t travel very far in a generation so gene flow is reduced. Because of their small size, snails are good to use practically rather than humans. In our investigation we are looking to see whether the polymorphisms are due to selection or simply genetic drift (which is always acting). Gene flow can also be a factor in differences in allele frequencies.

These processes are defined as follows:

[2] Natural Selection -­
 * Selection** is a process that acts on the genetic variation within a population. Under selection, individuals with advantageous traits tend to be more successful than their competitors. Darwin’s concept of natural selection is based on differential success in survival and reproduction. Individuals that have traits that are better suited to their environment tend to produce more offspring than those with traits that are not as well suited. When these traits have a genetic basis, selection can increase the prevalence of those traits, because offspring will inherit those traits from their parents. When selection is intense and persistent, adaptive allele frequencies become universal to the population or species.</range id="378282648_7">
 * Genetic Drift** is the change in frequency of an allele in a population <range type="comment" id="378282648_8">due to chance as the beneficial allele does not always end up being fixated.</range id="378282648_8"> Genetic drift causes alleles to fluctuate unpredictably from one generation to the next, populations (it has a bigger effect in smaller populations because the change in frequency of alleles from one generation to the next is much larger than in bigger populations.)

[3] Genetic Drift

<range type="comment" id="378282648_9">**Gene flow**</range id="378282648_9"> is the transfer of alleles or genes in or out of one population to another due to the movement of fertile individuals or their gametes.



[4] Gene Flow

The picture below shows our collection strategy at each site.

//Dark Green: Bush// //Light Green: Grass// //The black crosses indicate where will be collecting our from and each black cross has a distance of 20m.// //We have chosen to collect the samples along the same length as we want to keep the altitude a control variable.//
 * //Key://**

<range type="comment" id="378282648_11">‍‍ </range id="378282648_11"> Our null hypothesis is that there is no significant difference in the polymorphisms between the underlying populations of snails.

[1] Snails Polymorphism: http://www.bbc.co.uk/nature/adaptations/Polymorphism_(biology) [2] Natural Selection: http://evolution.berkeley.edu/evolibrary/article/evo_25 [3] Genetic Drift: http://evolution.berkeley.edu/evosite/evo101/IIIDGeneticdrift.shtml [4] Gene Flow: http://evolution.berkeley.edu/evosite/evo101/IIIC4Geneflow.shtml