Emmanouil*+final+write+up

**__Snail Day Trip Report __**
 * __SBS633 EvolutionaryGenetics __**
 * __Introduction __**

Polymorphism is a phenomenon defined as different alleles occurring at the same location and the same period of time. The evolutionary processes that play a role in polymorphism are selection, genetic drift (changes in allele frequency‍ due to chance), gene flow (movement of alleles from a population to another) and mutation. In this experiment, we studied the morph frequencies in populations of the extremely polymorphic brown-lipped snails //Cepaea nemoralis// and we established a correlation between altitude and frequency of phenotypes.

//Cepaea nemoralis // is a species of land snails mostly found in Europe and is mainly used for genetics and evolutionary studies. These snails are considered good model organisms as they ‍‘’carry their genes on their shells‍ and are highly polymorphic’’ (Jones et al, 1977). Traits include shell colour (yellow, pink or brown) and shell banding pattern (unbanded, middle banded and many banded). These snails are easier to study than humans mainly due to their small size and limitedmobility. As a result, genetic patterns will be limited to a small area thus enabling us to collect them in one locality and then studying their populations could be much easier unlike humans where gene flow is rather high.

The aim of this experiment, which was carried out in Pulpit hill near Monk’s Riseborough, is to examine the power of evolutionary processes such as genetic drift, selection and gene flow on the polymorphic distribution of alleles in //Cepaea nemoralis// and to see which of these processes has the strongest effect on thefrequency of alleles. Our sampling design enabled us to compare the phenotype of snails in different locations and consider what evolutionary process causes the observed samples.

The experimental design was carried out by observing the shell colour and band pattern of //Cepeae nemoralis// snails from different locations. Our group collected a minimum of thirty samples of snails from two different altitudes, uphill and downhill. Snails were collected from 4 different sites in those 2 altitudes (8 sites in total). Then, different variants of snails (shell colour and banding pattern) were recorded and a table was formed for comparison. The differences ‍could‍ be due to genetic drift, selection or gene flow. Our null hypothesis is that there would be no differences between phenotypic frequencies of the snails found at different altitudes.

If the polymorphism of snails is caused by natural selection, then phenotype frequency will vary with different types of habitats. Genetic drift may well also explain the differences in allele frequency between any pair of areas. For example, genetic drift could increase the frequency of a phenotype in one area, and of another phenotype in another area. However, it will not cause a constant association between a certain locality and the frequency of alleles.

‍The findings from this experiment will be analysed using a statistical chi squared test to see if differences are small enough to be recognized by sampling error and if the results indicate whether there is a significant difference between the phenotypes found between different locations. If differences were due to genetic drift or other random process, we would notice significant differences in phenotype frequencies.

The tables below provide a summery of the collected results by chi-squared tests to prove statistical significance between the different species and sites. Results are further discussed related to the proposed hypothesis deliberating any significance in the data between the upper and lower sites in the observed phenotypes.
 * __Results __**

__Figure 1- A total number of coloured phenotype observed uphill and the results of the chi- square statistical test. __

Ex= 4.88 X2= 0.0029  ||  8 <span style="font-family: 'Times New Roman',serif;">Ex=8.12 <span style="font-family: 'Times New Roman',serif;">X2= 0.0018  ||  <span style="font-family: 'Times New Roman',serif;">13   || <span style="font-family: 'Times New Roman',serif;">Ex= 12.75 <span style="font-family: 'Times New Roman',serif;">X2= 2.5931  ||  <span style="font-family: 'Times New Roman',serif;">27 <span style="font-family: 'Times New Roman',serif;">Ex=21.25 <span style="font-family: 'Times New Roman',serif;">X2=1.5559  ||  <span style="font-family: 'Times New Roman',serif;">34   || <span style="font-family: 'Times New Roman',serif;">Ex= 13.88 <span style="font-family: 'Times New Roman',serif;">X2= 8.9088  ||  <span style="font-family: 'Times New Roman',serif;">12 <span style="font-family: 'Times New Roman',serif;">Ex=23.12 <span style="font-family: 'Times New Roman',serif;">X2 = 5.3484  ||  <span style="font-family: 'Times New Roman',serif;">37   || <span style="font-family: 'Times New Roman',serif;">Ex= 7.5 <span style="font-family: 'Times New Roman',serif;">X2= 4.0333  ||  <span style="font-family: 'Times New Roman',serif;">18 <span style="font-family: 'Times New Roman',serif;">Ex=12.5 <span style="font-family: 'Times New Roman',serif;">X2= 2.42  ||  <span style="font-family: 'Times New Roman',serif;">20   || <span style="font-family: 'Times New Roman',serif;">d.o.f = (4-1)*(2-1) = 3*1 = 3 <span style="font-family: 'Times New Roman',serif;">Total x2 = 24.86 > 11.34 <span style="font-family: 'Times New Roman',serif;">Larger that the critical x2 0.01 value. We reject the null hypothesis.
 * <span style="font-family: 'Times New Roman',serif;">uphill  ||  <span style="font-family: 'Times New Roman',serif;">yellow   ||  <span style="font-family: 'Times New Roman',serif;">Pink &brown   ||  <span style="font-family: 'Times New Roman',serif;">total   ||
 * <span style="font-family: 'Times New Roman',serif;">Site 1  ||  <span style="font-family: 'Times New Roman',serif;">5
 * <span style="font-family: 'Times New Roman',serif;">Site 2  ||  <span style="font-family: 'Times New Roman',serif;">7
 * <span style="font-family: 'Times New Roman',serif;">Site 3  ||  <span style="font-family: 'Times New Roman',serif;">25
 * <span style="font-family: 'Times New Roman',serif;">Site 4  ||  <span style="font-family: 'Times New Roman',serif;">2
 * <span style="font-family: 'Times New Roman',serif;">total  ||  <span style="font-family: 'Times New Roman',serif;">39   ||  <span style="font-family: 'Times New Roman',serif;">65   ||  <span style="font-family: 'Times New Roman',serif;">104   ||

__<span style="font-family: 'Times New Roman',serif;">Figure 2: ____<span style="font-family: 'Times New Roman',serif;">A total number of banded phenotype observed uphill and the results of the chi- square statistical test. __ <span style="font-family: 'Times New Roman',serif;">Ex= 2.79 <span style="font-family: 'Times New Roman',serif;">X2 = 6.3527  ||  <span style="font-family: 'Times New Roman',serif;">6 <span style="font-family: 'Times New Roman',serif;">Ex=10.21 <span style="font-family: 'Times New Roman',serif;">X2= 1.7350  ||  <span style="font-family: 'Times New Roman',serif;">13   || <span style="font-family: 'Times New Roman',serif;">Ex= 7.29 <span style="font-family: 'Times New Roman',serif;">X2= 0.0115  ||  <span style="font-family: 'Times New Roman',serif;">27 <span style="font-family: 'Times New Roman',serif;">Ex= 26.71 <span style="font-family: 'Times New Roman',serif;">X2= 0.0031  ||  <span style="font-family: 'Times New Roman',serif;">34   || <span style="font-family: 'Times New Roman',serif;">Ex= 6.86 <span style="font-family: 'Times New Roman',serif;">X2= 5.0058  ||  <span style="font-family: 'Times New Roman',serif;">31 <span style="font-family: 'Times New Roman',serif;">Ex= 25.14 <span style="font-family: 'Times New Roman',serif;">X2= 1.3659  ||  <span style="font-family: 'Times New Roman',serif;">32   || <span style="font-family: 'Times New Roman',serif;">Ex= 4.07 <span style="font-family: 'Times New Roman',serif;">X2=0.9152  ||  <span style="font-family: 'Times New Roman',serif;">13 <span style="font-family: 'Times New Roman',serif;">Ex= 14.93 <span style="font-family: 'Times New Roman',serif;">X2= 0.2495  ||  <span style="font-family: 'Times New Roman',serif;">19   || <span style="font-family: 'Times New Roman',serif;">d.o.f = (4-1)*(2-1) = 3*1 = 3 <span style="font-family: 'Times New Roman',serif;">Total x2 =15.64 > 11.34 <span style="font-family: 'Times New Roman',serif;">Larger that the critical x2 0.01 value. We reject the null hypothesis
 * <span style="font-family: 'Times New Roman',serif;">uphill  ||  <span style="font-family: 'Times New Roman',serif;">unbanded   ||  <span style="font-family: 'Times New Roman',serif;">Many banded   ||  <span style="font-family: 'Times New Roman',serif;">Total   ||
 * <span style="font-family: 'Times New Roman',serif;">Site 1  ||  <span style="font-family: 'Times New Roman',serif;">7
 * <span style="font-family: 'Times New Roman',serif;">Site 2  ||  <span style="font-family: 'Times New Roman',serif;">7
 * <span style="font-family: 'Times New Roman',serif;">Site 3  ||  <span style="font-family: 'Times New Roman',serif;">1
 * <span style="font-family: 'Times New Roman',serif;">Site 4  ||  <span style="font-family: 'Times New Roman',serif;">6
 * <span style="font-family: 'Times New Roman',serif;">total  ||  <span style="font-family: 'Times New Roman',serif;">21   ||  <span style="font-family: 'Times New Roman',serif;">77   ||  <span style="font-family: 'Times New Roman',serif;">98   ||

__<span style="font-family: 'Times New Roman',serif;">Figure 3- A total number of coloured phenotype observed downhill and the results of the chi- square statistical test. __

<span style="font-family: 'Times New Roman',serif;">Ex= 36.76 <span style="font-family: 'Times New Roman',serif;">X2= 0.2072  ||  <span style="font-family: 'Times New Roman',serif;">27 <span style="font-family: 'Times New Roman',serif;">Ex=24.24 <span style="font-family: 'Times New Roman',serif;">X2= 0.3143  ||  <span style="font-family: 'Times New Roman',serif;">61   || <span style="font-family: 'Times New Roman',serif;">Ex= 18.08 <span style="font-family: 'Times New Roman',serif;">X2= 0.9207  ||  <span style="font-family: 'Times New Roman',serif;">16 <span style="font-family: 'Times New Roman',serif;">Ex=11.92 <span style="font-family: 'Times New Roman',serif;">X2=1.3965  ||  <span style="font-family: 'Times New Roman',serif;">30   || <span style="font-family: 'Times New Roman',serif;">Ex= 21.69 <span style="font-family: 'Times New Roman',serif;">X2= 0.2460  ||  <span style="font-family: 'Times New Roman',serif;">12 <span style="font-family: 'Times New Roman',serif;">Ex=14.30 <span style="font-family: 'Times New Roman',serif;">X2 = 0.3699  ||  <span style="font-family: 'Times New Roman',serif;">36   || <span style="font-family: 'Times New Roman',serif;">Ex= 17.47 <span style="font-family: 'Times New Roman',serif;">X2= 1.1746  ||  <span style="font-family: 'Times New Roman',serif;">7 <span style="font-family: 'Times New Roman',serif;">Ex=11.53 <span style="font-family: 'Times New Roman',serif;">X2= 1.7798  ||  <span style="font-family: 'Times New Roman',serif;">29   || <span style="font-family: 'Times New Roman',serif;">d.o.f = (4-1)*(2-1) = 3*1 = 3 <span style="font-family: 'Times New Roman',serif;">Total x2 = 6.409 < 11.34 <span style="font-family: 'Times New Roman',serif;">smaller that the critical x2 0.01 value .We accept the null hypothesis
 * <span style="font-family: 'Times New Roman',serif;">downhill  ||  <span style="font-family: 'Times New Roman',serif;">yellow   ||  <span style="font-family: 'Times New Roman',serif;">Pink &brown   ||  <span style="font-family: 'Times New Roman',serif;">Total   ||
 * <span style="font-family: 'Times New Roman',serif;">Site 1  ||  <span style="font-family: 'Times New Roman',serif;">34
 * <span style="font-family: 'Times New Roman',serif;">Site 2  ||  <span style="font-family: 'Times New Roman',serif;">14
 * <span style="font-family: 'Times New Roman',serif;">Site 3  ||  <span style="font-family: 'Times New Roman',serif;">24
 * <span style="font-family: 'Times New Roman',serif;">Site 4  ||  <span style="font-family: 'Times New Roman',serif;">22
 * <span style="font-family: 'Times New Roman',serif;">total  ||  <span style="font-family: 'Times New Roman',serif;">94   ||  <span style="font-family: 'Times New Roman',serif;">62   ||  <span style="font-family: 'Times New Roman',serif;">156   ||

__<span style="font-family: 'Times New Roman',serif;">Figure 4- A total number of banded phenotype observed downhill and the results of the chi- square statistical test. __

<span style="font-family: 'Times New Roman',serif;">Ex= 8.21 <span style="font-family: 'Times New Roman',serif;">X2 = 2.1588  ||  <span style="font-family: 'Times New Roman',serif;">57 <span style="font-family: 'Times New Roman',serif;">Ex=52.79 <span style="font-family: 'Times New Roman',serif;">X2= 0.3357  ||  <span style="font-family: 'Times New Roman',serif;">61   || <span style="font-family: 'Times New Roman',serif;">Ex= 4.04 <span style="font-family: 'Times New Roman',serif;">X2= 1.0300  ||  <span style="font-family: 'Times New Roman',serif;">28 <span style="font-family: 'Times New Roman',serif;">Ex= 25.96 <span style="font-family: 'Times New Roman',serif;">X2= 0.1603  ||  <span style="font-family: 'Times New Roman',serif;">30   || <span style="font-family: 'Times New Roman',serif;">Ex= 4.85 <span style="font-family: 'Times New Roman',serif;">X2= 7.7985  ||  <span style="font-family: 'Times New Roman',serif;">25 <span style="font-family: 'Times New Roman',serif;">Ex= 31.15 <span style="font-family: 'Times New Roman',serif;">X2= 1.2142  ||  <span style="font-family: 'Times New Roman',serif;">36   || <span style="font-family: 'Times New Roman',serif;">Ex= 3.90 <span style="font-family: 'Times New Roman',serif;">X2=0.0026  ||  <span style="font-family: 'Times New Roman',serif;">25 <span style="font-family: 'Times New Roman',serif;">Ex= 25.10 <span style="font-family: 'Times New Roman',serif;">X2= 0.0004  ||  <span style="font-family: 'Times New Roman',serif;">29   || <span style="font-family: 'Times New Roman',serif;">d.o.f = (4-1)*(2-1) = 3*1 = 3 <span style="font-family: 'Times New Roman',serif;">Total x2 = 12.70 > 11.34 <span style="font-family: 'Times New Roman',serif;">Larger that the critical x2 0.01 value. We therefore reject the null hypothesis.
 * <span style="font-family: 'Times New Roman',serif;">downhil  ||  <span style="font-family: 'Times New Roman',serif;">unbanded   ||  <span style="font-family: 'Times New Roman',serif;">Many banded   ||  <span style="font-family: 'Times New Roman',serif;">Total   ||
 * <span style="font-family: 'Times New Roman',serif;">Site 1  ||  <span style="font-family: 'Times New Roman',serif;">4
 * <span style="font-family: 'Times New Roman',serif;">Site 2  ||  <span style="font-family: 'Times New Roman',serif;">2
 * <span style="font-family: 'Times New Roman',serif;">Site 3  ||  <span style="font-family: 'Times New Roman',serif;">11
 * <span style="font-family: 'Times New Roman',serif;">Site 4  ||  <span style="font-family: 'Times New Roman',serif;">4
 * <span style="font-family: 'Times New Roman',serif;">total  ||  <span style="font-family: 'Times New Roman',serif;">21   ||  <span style="font-family: 'Times New Roman',serif;">135   ||  <span style="font-family: 'Times New Roman',serif;">156   ||


 * __<span style="font-family: 'Times New Roman',serif;">Discussion __**

<span style="font-family: 'Times New Roman',serif;">Results from 4 different sites of high and low altitudes were noted according the snails shell colour (yellow, pink and brown) and banding pattern (unbanded and many banded), where the majority of the snails that was collected were dead. Chi squared tests were conducted to demonstrate if the differences in allele frequency were due to genetic drift or selection, and estimates whether the difference in phenotype frequencies is statistically substantial. Results indicated a significant difference between the colour and band of //C. Nemoralis//, located at high or low altitudes as we have failed to accept the null hypothesis.

<span style="font-family: 'Times New Roman',serif;">Figure 1 and 2 rejects the null hypothesis where totals of x2 = 24.86 in Figure 1 and x2 =15.64 in Figure 2 were found to be larger than the critical value, demonstrating a greater abundance of darker coloured phenotypes (pink and brown) and many banded snails in the uphill sample.

<span style="font-family: 'Times New Roman',serif;">Figure 3 and 4 analyse the collected downhill results of the observed phenotypes. Figure 3 found no significant difference in the coloured phenotypes, showing a total of x2 = 6.409 being smaller than the critical value, thus accepting the null hypothesis. The null hypothesis was rejected in figure 4, where analysis of the banded phenotype found a total of x2 = 12.70 to be greater than the critical value.

<span style="font-family: 'Times New Roman',serif;">Results showed that within the uphill samples, there was found to be a greater expected value for many banded snails, and similarly the many banded snails were observed in the downhill samples. In this essence, taking account the coloured phenotype, yellow unbanded snails were found to have no statistical difference between the two regions, however yellow snail observations in general were found more prominently downhill. From these results, we can assume that at lower altitudes, there is less exposure to the sun and so there are fewer unbanded snails, this is because the more bands the snail has, the darker the shell will be, allowing it to acquire energy from the sun at a higher rate.

<span style="font-family: 'Times New Roman',serif;">However, limitations in our experiment may be due to sampling errors that affect our results, and could be reduced by increase the sampling size and replication of the study, i.e repeating the experiment many times. The experiment could have benefitted if we went on a rainy day, as opposed to the fairly dry day when the experiment was conducted, as the ideal environment for snails is rainy and wet, which can explains why most snails we found were dead. Furthermore, the studied area was open to public; hence the collected samples may not be an accurate representation of the snail population. Finally, our collected samples may have been more accurate with the use of a quadrant.

<span style="color: #262626; font-family: 'Times New Roman',serif;">In conclusion, the results indicate the significant differences can be attributed to factors involved in natural selection as indicated above, however these observed differences can also be found to be due to genetic drift. Research supporting this by Jones et al. (1977) suggested that these differences in morph frequencies can be due to genetic drift.


 * __<span style="font-family: 'Times New Roman',serif;">References __**

<span style="font-family: 'Times New Roman',serif;">Jones, J. S., Leith, B. H. and Rawlings, P. (1977). Polymorphism in Cepaea: a problem with too many solutions? Ann Rev Ecol Syst, 8: 109–143.


 * __<span style="font-family: 'Times New Roman',serif;">Group Members: __**
 * <span style="font-family: 'Times New Roman',serif;">Emmanouil Apostolidis*
 * <span style="font-family: 'Times New Roman',serif;">Ahad Al-Seraihi
 * <span style="font-family: 'Times New Roman',serif;">Aliya Abilmazhinova
 * <span style="font-family: 'Times New Roman',serif;">Charisse Fallaria
 * <span style="font-family: 'Times New Roman',serif;">Christopher Constantinou
 * <span style="font-family: 'Times New Roman',serif;">Fatima Islam
 * <span style="font-family: 'Times New Roman',serif;">Zanjani Shadman

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