A.Ali+group+introduction

__**Evolutionary Genetics Day****Trip at Monks Riseborough.**__ =**Introduction**=

Polymorphism is the occurrence of multiple alleles in a population of a species at a specific gene locus. Three underlying processes which help explain the existence of polymorphism are; genetic drift & selection which account for the spread or loss of allele frequency and mutations that produces different alleles. Genetic drift itself is a change in allele frequency within a population due to chance, with its effects greater in small populations in comparison to larger ones. The third, gene flow, is the movement of alleles from one population to another. We hope a to conclude which of the processes affect the frequency of alleles in our study.

In this study we will use //Cepaea nemoralis// as a model species as it is a land snail that lives in woods and open grasslands hence the study took place at Monks Riseborough. The species is polymorphic with shell colours pink, yellow and brown with the number of bands differing from 0-5. The reason for choosing snails rather than humans is due to their slow locomotion over a generation, due to snails being restricted to survival in specific habitats, therefore it can be suggested that h a greater population density may be found in one area allowing for genetic differences to accumulate. In more mobile species such as b humans, population genomes are widely spread hence gene flow is much greater. Another reason is that the //Cepaea // species, although cross fertilising hermaphrodites[1], have differences in their anatomy[2] and so hybrids are very rare[3], making it possible to trace genetic differences to parental generations. They are also easier to collect and examine than humans, due to their small size and easily identifiable phenotype traits. In addition, studying humans is rather more complicated due to cost (from analysing data to possible c monetary incentives which might be needed to study a large sample of the population), permission and ethical issues f which can arise e.g. classifying races and obtaining consent.

Previous studies have shown that populations found at the boundaries of habitats exhibit more composite phenotypic traits due to gene flow[2]. Also selection in favour of dark coloured species is found in shrub areas due to ability to stay conspicuous and thus evade predators[4]. On the other hand lighter coloured snails with fewer bands have shown the ability to survive better in warmer climates, as they are able to i reflect light and appear less noticeable to predators[2]. We hypothesise that in the open grassland, lighter coloured snails with fewer bands (between 0-3) will be observed, and in habitats consisting of shrubs and short trees we expect to find darker snails with a greater number of bands (4-5). The b differences could simply be attributed to genetic drift which occurs randomly. If genetic drift is the sole reason for differentiation g then the relationship between phenotype and environment should be random and no correlation will exist. Moreover, if it is due to gene flow then there will be multiple polymorphic traits, whereas if selection or negative frequency dependant selection is acting then there would be less variation at specific sites.

500 words

Result: =Results:= The raw results as collected from the **shrub** site:
 * **Shrub Sites** || **LIGHT (0-3 Banded Pink/Yellow)** || **DARK (All brown + 4-5 banded Pink/Yellow)** || **Totals** ||
 * **Site 1** || 9  ||  18  ||  **27**  ||
 * **Site 2** || 8  ||  9  ||  **17**  ||
 * **Site 3** || 11  ||  24  ||  **35**  ||
 * **Totals** || **28**  ||  **51**  ||  ** 79 **  ||

The expected values for the above results have been calculated as below. The Final Chi-squared value: 1.302
 * **Expected Values** || **LIGHT (0-3 Banded Pink/Yellow)** || **DARK (All brown + 4-5 banded Pink/Yellow)** ||
 * **Shrub Site 1** || 9.57  ||  17.43  ||
 * **Shrub Site 2** || 6.03  ||  10.97  ||
 * **Shrub Site 3** || 12.41  ||  22.59  ||

We can conclude that there is no significant difference between the different shrub sites ( c2 =1.302, df=2, p=5.99 at 5% level)

The results as collected from the **grass** sites:
 * **Grass land** || **LIGHT (0-3 Banded Pink/Yellow)** || **DARK (All brown + 4-5 banded Pink/Yellow)** || **Totals** ||
 * **Site 1** || 10  ||  7  ||  **17**  ||
 * **Site 2** || 11  ||  9  ||  **20**  ||
 * **Site 3** || 13  ||  6  ||  **19**  ||
 * **Totals** || **34**  ||  **22**  ||  ** 56 **  ||

The expected values for the above results have been calculated as below.
 * **Expected Values** || **LIGHT (0-3 Banded Pink/Yellow)** || **DARK (All brown + 4-5 banded Pink/Yellow)** ||
 * **Grass Site 1** || 10.32  ||  6.68  ||
 * **Grass Site 2** || 12.14  ||  7.86  ||
 * **Grass Site 3** || 11.54  ||  7.46  ||

Final Chi-squared value: 0.772 We can conclude that there is no significant difference between the different grass sites ( c2 =0.772, df=2, p=5.99 at 5% level)

As there have been no significant differences found between the different grass sites and shrubs sites, we can pool all the grass sites and all the shrub sites to make a comparison and find out whether any difference exists in terms of snail banding and colour between the two types of sites.

The pooled data for comparison between shrub and grass:
 * || **LIGHT (0-3 Banded Pink/Yellow)** || **DARK (All brown + 4-5 banded Pink/Yellow)** || **Totals** ||
 * **Shrub** || 28  ||  51  ||  **79**  ||
 * **Grass** || 34  ||  22  ||  **56**  ||
 * **Totals** || **62**  ||  **73**  ||  ** 135 **  ||

The expected values for the above data:
 * **Expected** || **LIGHT (0-3 Banded Pink/Yellow)** || **DARK (All brown + 4-5 banded Pink/Yellow)** ||
 * **Shrub** || 36.28  ||  42.72  ||
 * **Grass** || 25.72  ||  30.28  ||

Final chi-squared value: 9.019 We can accept our alternative hypothesis ( c2 =9.019, df=1, p=6.64 at 1% level)

**Discussion**
We hypothesised that in grassland habitats, lighter coloured snails with fewer bands will be observed, and in shrub land habitats, darker snails with a greater number of bands will be present. Our null hypothesis being that there will be no significant difference found between the habitats. The chi square results obtained indicate a statistical difference of phenotypic traits present at the two habitats that were analysed. A pattern in favour of light and fewer bands was observed in the grass habitat against the dark snails observed in the shrub habitat. This pattern correlates with other research studies carried out on //Cepaea nemoralis //polymorphism such as Jones (//1977) //which have shown similar findings. Apart from one shrub site, where the number of dark coloured shells was 1 less than light, the second and third shrub sites showed a difference of 9 and 13. When combined, the number of dark snails (51) is almost double that of light (28) in the shrubs which supports our hypothesis. However, the difference (12) in the grass habitat was not as large. Although this pattern may be a result of higher predation in the open grassland.

In reflection of our study the research was constrained to time and sunlight which could be bettered if it was carried out in the summer, allowing more sunlight and time to be spent in the reserve. Our experiment was carried out on a cold and dry day, which was not ideal as //C. nemoralis // like to emerge in warm and wet, thus our findings consisted of mainly dead snails. Also our observations were based on one day, therefore to improve reliability it may be suggested to take observations over a number of days, possibly spread throughout the year. Furthermore, other groups researched //Cepaea // polymorphism on the same day and so our results may have been skewed, as we observed clusters of snail shells at sites, which maybe a result of groups misplacing samples. Data found in such an arrangement should be avoided in future experiments. The reserve is open to the public so habitats may have been disturbed due to human and pet locomotion.

Our findings concur with our hypothesis; however concrete conclusions can not be made owing to factors such as sampling error. In order to reduce sampling error, more sampling sites should have been analysed. If time permitted, we could have repeated the experiment numerous times in each site and then attained an average. This would increase the accuracy, as similar results would indicate that there is a correlation rather than the results being due to human error or possibly even genetic drift. Moreover, a small sampling size does not represent the total population. Unfortunately we observed a small number of snails, therefore it would be difficult to generalise the results to larger populations.

In conclusion, the consistent pattern we observed of expected phenotypic traits that correlated to differences in the environment, suggest selection as the most probable process acting on the population. Genetic drift would produce differences uncorrelated with the environment, hence that may be ruled out as the key factor in light of our results.


 * __References__**
 * 1) Aubertin, D. 1927. On the anatomy of the land snails (Helicidae) Cepaea hor- tensis (Mull) and Cepaea nemoralis (L.). Proc. Zool. Soc. London 1927: 553-82
 * 2) Perrot, J.-L., Perrot, M. 1938. Mono- graphie des Helix du groupe Cepaea. Contribution a la notion d'espece. Bull. Biol. Fr. Belg. 72:232-59
 * 3) Lang, A. 1908. Uber die Bastarde von Helix hortensis Mueller und H. nemor- alis L. Festschr. Univ. Jena 1908:1-120
 * 4) Cain, A. J. 1953. Visual selection by tone of Cepaea nemoralis. J. Conchol. 23:333-36
 * 5) Brooker .J.R. (2009). //Genetics Analysis & Principles// 3rd edition. New York: McGraw-hill.

Group Members: Aman Ali, Bilal Tailor, Muhammad S Hasan, Moon Cherng, Mohsinoor Yemani