ME&+Tripple+S


 * __Introduction to a study on Polymorphism using //Cepaea nemoralis// snails__**

Polymorphism is a common evolutionary feature that occurs in nature where two or more clearly different phenotypes exist in the same population of a species. today, polymorphism is really defined on the basis of the genotype The aim of this experiment is to study the effect of evolutionary processes such as natural selection, gene flow and genetic drift on the polymorphic distribution of //Cepaea nemoralis//. Cepaea does not have a 'polymorphic distribution' I think you mean the distribution of alleles //C.nemoralis// will be used as a model organism because they are hermaphrodites so the effect of sex linkage can be disregarded nope, that is far from the reason. The snail banding patterns show clearly distinguishable phenotypes, making the study of polymorphs much simpler than in higher organisms its nothing to do with the complexity of the organism such as humans whose allelic differences can be quite subtle so can snail polymorphisms, in both humans and snails some traits have a phenotype determined in a simple fashion by one or a few loci, in a straightforward way (how about eye colour in humans?). Snails move slowly, therefore genetic differences build up over short distances thus allowing us to observe them in one locality. In larger, faster moving species such as humans, population genomes are more widely spread and gene flow is also much higher. Studying simpler organisms such as //C.nemoralis// snails allows us to distinguish more clearly between the effects of genetic drift, gene flow and selection on differences in allele frequencies between populations why should simpler organisms have simpler patterns? , allowing information to be collected, which could then be applied to many species including humans. In carrying out our various sampling methods during this investigation, we hope to find out if the different habitats have different phenotype frequencies and whether gene flow is occurring between these habitats, and to what extent. We will investigate which evolutionary process has the strongest effect on distribution of //C.nemoralis// phenotypes. how will you tell what is going on? Our mode of sampling will be systematic; taking 3 samples of populations within 2 different habitats; woody(shrubland) areas and non-woody(grassland) areas. The sample areas will be large enough to allow us to get at least 40 snails in each sample, providing an accurate representation of the entire population. Samples within each habitat will be adequately spaced away from each other and from habitat boundaries; attempting to reduce the effects of gene flow and ensure the samples remain separate and distinguishable unclear, why does this require reduced gene flow? . This sampling method allows us to focus on the distinct differences between the habitats, giving us control over other variables that might affect our results, i.e. differences in factors within the same habitat such as vegetation present, light intensity, wetness, etc. Performing 3 repeats in each habitat increases the validity and accuracy of our results why, spell out the logic. Restricting the investigation to one side of one valley allows us to get samples at similar heights and hopefully removes other variables that would arise from sampling across the valleys such as changes in soil type, altitude, wind intensity and rain fall; allowing us to focus on just the differences between the two types of habitat. We believe that natural selection will be the main evolutionary process affecting the phenotypic distribution of //C.nemoralis// within the valley. We expect to see greater proportions of darker snails in woodland areas and lighter snails in open areas due to selection pressures. However if allele frequencies are similar in both populations, this would indicate a high incidence of gene flow and the continuous action of genetic drift. but surely genetic drift causes difference in allele frequency between different localities, so how will you distinguish the effect of drift from the effect of selection?

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Marium Sherwani - 090134663 Etomby Namme - 090129407 Shaima Al-Zawawi - 090137240 Sabrina Brown - 090128259 Samaah Haque - 090141269