Charlotte's+Group

  **__Introduction__**

Genetic variations variation (or variants)  shown in the phenotype within the same species may be explained by various evolutionary processes. These genetic variations ditto can be operated on by natural selection and this phenomenon is known as polymorphism no, the action of selection is not known as polymorphism. The existence of alleles at a locus is. . The genus Cepaea  are terrestrial snails in the class Gastropoda these show a perfect display of the polymorphism concept. Within the species C. nermoralis there is a great variation in shell colour (pink, yellow and brown) and the number of bands present on the shell (0-5 and if present the bands can be punctuate define ). Adults and sub-adults can be differentiated from each other by the lip colour at the opening of the shell; adults have a black lip and sub-adults have a white lip.  <span style="color: windowtext; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 80%; margin-bottom: 30pt; margin-left: 0cm; margin-right: 0cm; margin-top: 26pt; text-align: justify;"> <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 80%;">The study of polymorphism in <span style="color: windowtext; font-family: 'Times New Roman Italic','serif'; font-size: 12pt; line-height: 80%;">Cepaea <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 80%;"> is more advantageous than studying humans. Firstly, studying humans would bring rise to ethical issues. Unlike humans <span style="color: windowtext; font-family: 'Times New Roman Italic','serif'; font-size: 12pt; line-height: 80%;">Cepaea <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 80%;"> have a shorter life span allowing immediate comparisons to be drawn between the live and dead. doubtful, all snails die in the end, so what do you learn by comparing the shells of dead snails with live ones (something about changes through time perhaps) <span style="color: windowtext; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 80%;"> Snails are able to reproduce after a year, whereas humans take longer to reach sexual maturity. Therefore generations of snails can be studied in shorter periods of time is this done much, does that explain why //Cepaea// studies have been so informative <span style="color: windowtext; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 80%;">. These organisms produce a larger progeny compared to humans, supplying us with a greater population to sample you are telling me there are more snails than humans, really? <span style="color: windowtext; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 80%;">. This increases the likelihood of finding variation within our sample why? How does large family size increase polymorphism? <span style="color: windowtext; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 80%;"> so that results obtained are more or less representative of the larger population and conclusions are more easily drawn logic unclear, and probably wrong <span style="font-family: 'Times New Roman',serif; font-size: 16px; line-height: 12px;"><span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 80%;">. Snails are smaller organisms and so are easier to handle. The genotypes of <span style="color: windowtext; font-family: 'Times New Roman Italic','serif'; font-size: 12pt; line-height: 80%;">Cepaea <span style="color: windowtext; font-family: 'Times New Roman','serif'; font-size: 12pt; line-height: 80%;">reflected directly in the phenotype therefore if gene flow, genetic drift or natural selection occurs it is observable in the phenotype of the snail, such as shell colour doesn't human phenotype reflect genotype quite easily, eg eye colour? <span style="font-family: 'Times New Roman',serif; font-size: 16px; line-height: 12px;">. <span style="display: block; margin-bottom: 10pt; margin-left: 0cm; margin-right: 0cm; margin-top: 0cm; text-align: justify;"><span style="color: windowtext; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 80%;"> <span style="color: windowtext; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 80%; margin-bottom: 30pt; margin-left: 0cm; margin-right: 0cm; margin-top: 26pt; text-align: justify;"> Evolutionary processes have a vital role in creating and maintaining polymorphism. Gene flow involves the movement of genes between populations through the movement of individuals or gametes to increase variation within a population. Genetic drift occurs where there are changes in allele frequency within a population; certain alleles may be lost or fixed due to random events such as natural disasters or mating success. Natural selection is where individuals with characteristics better adapted for survival are selected for. Meaning those individuals can live and reproduce to pass on those traits successfully whereas less adapted individuals are eliminated. <span style="color: #ff0000; font-family: arial,helvetica,sans-serif; font-size: 13px; line-height: 19px;"> OK these are different processes, but how will you tell which is acting on the //Cepaea//?

<span style="color: windowtext; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 80%; margin-bottom: 26pt; margin-left: 0cm; margin-right: 0cm; margin-top: 10pt; text-align: justify;"> We will try to prove that the differences in shell colour and banding is due to natural selection in response to environmental pressures. Our hypothesis is that in woodland there will be darker coloured, highly banded shells because of camouflage among dead leaves, mud and tree roots. Whereas in shrubbery there will be highly banded, lighter-coloured shells due to the presence of twigs and exposure to light. These adaptations can be explained by natural selection as colouring and banding of shells will protect the snails from predators such as Thrushes. Finding similar quantities of the different coloured shells in all areas would disprove our hypothesis. <span style="color: #ff0000; font-family: arial,helvetica,sans-serif; font-size: 13px; line-height: 19px;"> but drift could produce a difference in allele frequency between two habitats, so how will you tell if its drift or selection?

<span style="color: windowtext; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 80%; margin-bottom: 26pt; margin-left: 0cm; margin-right: 0cm; margin-top: 10pt; text-align: justify;"> Stratified random sampling will be our sampling method. It is un-biased and captures the key population characteristics in the sample and therefore can be generalised to the overall population. <span style="color: #ff0000; font-family: arial,helvetica,sans-serif; font-size: 13px; line-height: 19px;"> not explained.

<span style="color: windowtext; font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 80%; margin-bottom: 10pt; margin-left: 0cm; margin-right: 0cm; margin-top: 0cm;"> **Contributions:** Naima Leeoza, Aysha Patel, Jinsy Jose, Noor El-Hassan and Charlotte Sarah Louise Christian