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code Title: The extent and effect of genetic drift and natural selection on the speciation of Cepaea populations

Introduction

Evolution is driven by natural selection and genetic drift. Selection acts with direction based on driving heritable phenotypic adaptations to the environment. what about balancing selection Conversely drift acts on the genetic frequencies with chance code code and no regard for phenotype. The question at hand is to what extent does each factor contribute to the final outcome of phenotypic frequencies?

A phenotypic trait that provides evidence for both selection and drift in a population is that of Polymorphism polymorphism is not a phenotypic trait, as I understand the term. This is the biological instance when code code there is more than one morphological appearance in modern terms, surely its the existence of multiple alleles- you might have genetic polymorphism not discernable in the phenotype of a species within the code code same panmictic (random mating) population, habitat and time frame (Ford 1965).

Cepaea nemoralis (the grove snail) is a renowned example of polymorphism. Their shells show extensive amounts of diversity ranging in colour (brown, pink and yellow) and also in the number of longitudinal bands present (five to none). Such distinct phenotypes, along with widespread populations, unsuspecting nature and their ability to cross-fertilise as hermaphrodites make these molluscs’ ideal candidates for investigation. code  say something about the mapping of genotype onto phenotype

Through the following experiment we aim to determine the extent and effect of genetic drift and natural selection on the speciation of snail populations in a particular habitat. We will do this by observing historical frequencies of snail phenotypes (in the form of discarded shells and fragments) in given areas, and comparing them with the phenotypes of the current living population in the same areas. The results will determine which phenotypes are being more frequently selected for.  what is the logic here, if the dead are different from the live, that implies the allele frequency has changed, but that could be due to drift could it not? Further to this we will compare the results between 3 or 4 populations to discern whether the resulting phenotypes are based on natural selection or genetic drift.  how will you tell them apart? Here we hypothesize that we will observe a relatively constant correlation between the phenotypic frequency of dead and living snails in a particular location.

We can predict that the observations will show that natural selection is working towards fixing a particular phenotype if those in historical frequencies are the same as in current frequencies. what if the environment has changed. Eg you could see that bushes had recently been cut down to make more open areas However we can also code predict that the occurrence of genetic drift within a population will give rise to varying phenotypes existing in the different generations. Providing there is no gene flow between the populations analysed, we would expect to see that all the sampling areas would show similar frequencies, but slightly differing phenotypes.

code  you haven't really said how you would incisively tell apart different explanations of the geographic pattern Our null hypothesis would be that we would observe no trend or constant correlation between frequency of dead and alive snails at a certain location.

Contributing Members: Jade Lam Elisa Brann Dominique Mckenzie-Spooner Sioban Banful