Snail+Trail

=Group name: Snail Trail=

__Members:__

Lara Al-zou'bi * Natasha Lauffer Natalia Izotova Ridhika Poojara

__Introduction__

In population genetics, polymorphism plays a large role in the genetic diversity of species. It is the allele differences within a species that gives rise to the variation in traits that are observable. At the DNA level, polymorphism is due to two or more alleles that influence the of the individual that inherits them ( Klug and Cummings, 1997). This is common in nature and common amongst humans. Examples of polymorphism in humans include the different forms of haemoglobin and blood type ( F Vogel et al, 1997) .

Polymorphism arises due to mutation, however several factors such as genetic drift, gene flow and natural selection maintain polymorphism in a population ( Kimball's Biology Pages 2011). In this investigation, we will be investigating the factors aforementioned by studying the polymorphisms in Capaea nemoralis (the grove snail). The reason behind studying this species of snail is because can exist in several colours and banding patterns. In addition to that, C. nermoralis do not travel very far and move at a slow pace within a small area. Thus this makes it an easy model to sample as opposed to sampling in humans for instance which requires sampling across continents. Other advantages regarding studying C. nemoralis include the fact that it is ethical, since the study is able to include shells of dead snails and therefore displacing the living organisms is not a problem. The main objective of the study is to sample different habitat areas and seeif there are observable significant differences. If there are significant differences, it can be inferred that selection, genetic drift or human/ sampling error have taken place. If there the observable differences are not significant, then there is no clear-cut evidence to back up selection, genetic drift or human/ sampling error. Sampling strategy:



The sampling took place across two habitat types: woodland and grassland. From this sampling, the polymorphisms between both populations will be compared as well as the intermediate area between them (which is still grassland). With that in mind, we have kept the populations approximately 20m ap<range type="comment" id="380835596_9">art to avoid gene flow between</range id="380835596_9"> the adjacent populations. To further enhance our study we have carried out replicate samples to help us deal with the possibility of other explanations for any significant differences. We kept away from shrubs as this is a different population with its independent variabes and tried to keep other environmental factors constant such as sampling on the same day with the same weather conditions and tried to carry out the sampling within a similar altitude.

It is worth mentioning that despite the 20m distance between populations, looking at the intermediate area to see change/similarity in frequencies could give us in insight into recognising gene flow as the distance between the populations does not mean that the populations are unaffected by gene flow. From our sampling we were hoping to be able to identify whether polymorphism, that we expect to find among snails in this area, is due to genetic drift or selection. If it’s due to natural selection we would expect to see a pattern of colour and band distribution within the different populations. For example, we would expect to find more brown coloured snails in the woodland. <range type="comment" id="380835596_10">Brown colour would be a benefit for the snails that live on the ground, because it would be hard for predators to find them. </range id="380835596_10">If it’s due to genetic drift we would expect to see random distribution of the same features. For example, we could find that in one population that lives in woodland brown colour is prevalent, but in another population in the woodland the other colour is <range type="comment" id="380835596_11">dominant</range id="380835596_11">. <range type="comment" id="380835596_12">This would show us that there is no selection against the colour, and that the dominance of one colour over another is just a random event based only on the chance alone.</range id="380835596_12"> Null Hypothesis:
 * The difference in allele frequencies is not significant between populations and therefore the polymorphism od snails is attributed to selection.
 * Frequencies are significantly different; polymorphisms are not in the same frequencies.

Alternative Hypothesis:


 * The difference in allele frequencies is significant between populations therefore polymorphism of snails is attributed to genetic drift and gene flow.
 * Frequencies are not significantly different; polymorphisms are in similar frequencies.

Bibliography


 * Klug and Cummings, (1997). **// Concepts of Genetics //** . 5th ed. New Jersey: Prentice-Hall, Inc. page 696.

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 * F Vogel et al, (1997). **// Human Genetics: Problems and Approaches //** . 4th ed. New York: Springer page 553.

World Wide Web

Kimball's Biology Pages (2011). **// Polymorphisms //**. [ONLINE] Available at: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Polymorphisms.html#How_do_polymorphisms_arise. [Last Accessed 8/11/12].