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Natural selection and allele frequency

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1. A population of Madagascar hissing cockroaches lives in a woodpile. It suffers heavy predation from lizards, which pull the roaches out of their hiding places. The largest adults are not able to fit into most of the cracks in the wood, and are hunted down mercilessly, and the smallest adults are easily pried out of their crevices. The other roaches usually survive.

What type of selection are the lizards likely to impose on the cockroaches?

2. Wild tobacco plants with a single, dominant mutation are resistant to herbivory by hornworms (sphynx moth larvae). As a result, they grow larger and set many more seed. In areas where hornworms are present, what type of selection do they impose on tobacco plants?


Solution Preview

There are three types of natural selection which can impose a change in allele frequency:
1. directional selection
2. stabilising selection
3. disruptive selection

Question 1.
This would be stabilising selection. This occurs when the environment does not change and as a result there is no pressure for a well-adapted species to change. An example of this is the coelocanth, a fish species known only from ancient fossils and assumed to have been extinct until a ...

Solution Summary

This problem set deals with two questions about natural selections. The solutions for each question are fully answered and further reading is also outlined. The attached word document contains the two questions.