Humus+&+Peter

group 5's (Humus and Peter) **__Introduction for the evolutionary genetics day trip.__** Polymorphism describes a situation in nature whereby two or more different phenotypes occur in one environment and the phenotypes are able to live in the same population if they can occur, surely they can live there. Also, is it the genotypes or phenotypes that need to differ if the population is to be classified as polymorphic? . The phenotypes observed to vary in //Cepaea nemoralis are// the number of bands and the colour of the shell in both dead and alive adults and sub-adults. The colour of shell ranges from brown to pink to yellow, and the number of bands observed ranges from 0-5. One can differentiate between adults and sub-adults by the presence of a band around the lip of the shell in adults and absence of this in sub-adults. This experiment is to determine the distribution of snail’s (//Cepea nemoralis//) phenotype across high woodland and low woodland allowing us to determine which alleles are most suitable for the differing altitudes but how you will tell the effects of selection from those of drift? . The data will be collected to form a χ2 test which be eventually used to test the null hypothesis. Snails are used for this type of study because there is no ethical conflict of manhandling them, there are large populations of them concentrated in small areas, differences are easily distinguished even when dead can still be studied from their shell and there is a huge body of information is already known about //Cepea nemoralis//. There is also the probability that the finding from the patterns of population distribution not really, its the understanding of the interaction between drift, gene flow, and selection that can be applied more widely, can be applied to other organisms. In the experiment we decided have decided to do two samples of woodlands at high and low altitudes all under as similar conditions as possible. For example with the same trees, no moss, same tree density, leaf debris thickness and facing the same direction. Two samples are taken so chance occurrences of one type of snail in one location could be viewed as an anomaly caused by genetic drift. is two enough? There are expected to be different microenvironments at changing altitudes resulting in certain phenotypes being more successful in different areas. This could result in large percentage differences between the distributions of certain traits do you mean the frequency... actually, do you need strong selection to produce large differences in frequency? Can't weak selection over a long time produce the same? . One would expect to find that in areas with a high abundance of similar adult shells would indicate that the death rate (due to predation or adaptation to surrounding environment) was lower for that particular phenotype. I don't understand your logic, lots of dead shells could indicate a high population density (as all snails die eventually) or that an environment where it is easy to see dead shells, or one where they are preserved for longer. As the altitude changes there may be different predators, predating at varied rates. If there is no clear distribution between the two altitudes then it would mean that the altitude difference was not enough to act on the phenotypes differently, or the colour and banding have no difference on survival at the two altitudes. how about the possibility that there is extensive gene flow? or insufficient time for selection to act?

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