James,+Sophia,+Alex,+Varvara,+Kim+discussion

"Yellow was the most frequent shell colour within the sampled population, the yellow allele is recessive to all other colours, (Jones et al 1977). Thus, it can be deduced this is the most common allele, as each yellow snail must possess two copies of the yellow allele at the locus, as well as it possibly being found as a recessive, non-expressed variant in both brown and pink snails.  Brown was the least common phenotype observed, and is a dominant trait. Each snail displaying a brown coloured shell must posses at least one brown allele, if not two in homozygous individuals. The frequency of the pink allele is hard to assess, as it may be heterozygous with both yellow, thus expressing the pink phenotype, or brown, expressing the brown phenotype. As all of the calculated chi squared values were found to be insignificant at the ninety-nine percent level of probability, the null hypothesis can be accepted. It would be expected that less than one percent of trials would show statistical significance. This means that there is no significant difference in the dominant allele frequency between populations. It can therefore be concluded that natural selection is not a major component in the distribution of the C. nemoralis shell polymorphism between grassland and shrubbery, or over a vertical zonation. This is not to say, however, that natural selection does not occur in the population at all and evidence of bird predation was observed in the broken shells of several individuals. Further study on the predators in the area and their distribution may yield further information on the significance of this factor. Based on the observed patterns and resulting chi squared values, it can therefore be deduced that genetic drift appears to be the largest factor in the allele distribution patterns as all areas show insignificantly different distributions. It is also possible that the lack of significance could be caused by gene flow from other communities, negating the effect of selection across the population. However, as there was no significant difference between samples it is unlikely that this is the case. Bottleneck populations are also unlikely as there was no significant difference between sites and thus the bottleneck would have to have acted across a large proportion of the hill side, and with no evidence of a large scale disturbance this is unlikely to be the case.  Given the wide spread of samples taken, and the expected distance that an individual of the C. nemoralis species could travel in a lifetime, the possibility that all observed phenotypes originated from the same population is unlikely. However, snail eggs have been known to be dispersed quite widely on the feet of birds, (Jones et al, 1977), and it is possible that several smaller populations originally dispersed in such a manner may be experiencing gene flow between one another in the locality of the study. "