Green+Team

Evolutionary Genetics Snail Trip Introduction The purpose of our trip is to study the polymorphism of the land snail //Cepaea//, focussing on the colour and number of bands exhibited on their shells. We will examine the variation in gene allele frequency by sampling the different phenotypes you'll sample the snails and record/score the phenotypes from variety of sites to determine any discernable relationships vague. Analysis of several areas may be able to highlight potential genetic mechanisms or evolutionary processes at work such as natural selection or genetic drift, with a specific colour/ring combination visibly spreading into different habitats or groups of snails. vague again We are looking at snails as they are easy to study. Due to limited mobility in a snail’s lifetime most populations I think you mean the genetic patterns, the populations might go on for miles in some areas are contained within a reasonably small area. This means that any genetic drift or variation etc, would occur in a very small space and so the differences are easily observable. If we wanted to study humans then samples would take a long time to collect due to the fact that humans as a single species have covered the entire world. snails are present all over the world too... its the scale of the patterns which is the issue The fact that humans can travel practically anywhere also means that the effects of genetic drift and variation are very wide spread and would be very hard to establish really? Possibile in major cities, but what about e.g. alpine valleys? . The small areas that snails live in are also advantageous as it makes the taking of a sample very easy. There are also fewer ethical concerns with studying snails then there would be with humans as elements such as consent do not apply. The snails act as a model organism, with any knowledge gained being applied to other species including humans due to universal evolutionary and genetic mechanisms. We can use comparisons in the data collected to determine any genetic mechanisms that may be influencing the phenotype of the snails shell colour and the number of bands that are displayed you've said this several times now, but how? . If the phenotypes were selected for naturally, then we would expect to find the dominant no,no don't use the word dominant to mean frequent in genetics, it gets confused with the Mendelian meaning, phenotype changing consistently with the environment in which it is based, as that is where it conveys the most fitness imprecise, spell out how selection would work 'the environment where it is based' is not the issue. . Bottlenecks would create very few phenotypes which would then expand dramatically, resulting in large areas with the same phenotypes with very little variation between them. Patterns of genetic drift could be discerned from a single phenotype being detected in different samples; with the number decreasing the further away from the ‘source’ the samples are taken. This would exhibit that particular phenotype travelling through different snail populations and therefore spreading. OK, but drift can also act more subtly on existing polymorphism, without leading to the fixation of only one phenotype. It could simply increase the frequency of one phenotype in one locality, and of another in a different locality Our group will collect samples of snails from different locations throughout the valleys at Pulpit Hill. The habitat that the snails will be taken from will be kept the same and elements such as altitude etc, will be kept as similar as possible. The aim of the experiment is to determine whether or not there is any genetic drift of particular phenotypes between the samples that are taken and whether or not the phenotypes occur in the same frequencies. but how would you tell, in particular who will you distinguish between drift causing, say, more brown in a bushy area from selection doing the same? Our null hypothesis is that all sites will have the same frequency and identical phenotypes.

Contributing Members: Graham Berreen Ying Cheung Catriona Brewin Nazim Khan