Natural Selection Homework assignment (10 points) Due next class period Students

Question

Natural Selection Homework assignment (10 points)

Due next class period

Students are to do this assignment independently

For one of the examples given below, explain how natural selection may have led to the evolution of the trait by answering these 5 questions. Type your homework, with answers numbered 1 - 5 and using complete sentences.

1) Identify the trait that you will describe and how that trait is beneficial to the species?

2) If you could go back in time and examine the ancestral species, would all of the organisms have looked identical? Describe the variation that may have existed within that ancestral species and which provided the ‘raw material’ for natural selection.

3) Why didn’t all of the offspring of these organisms survive? What type(s) of 'selective pressure' would have favored evolution of this trait?

4) Which organisms within the species would have been most reproductively successful? What does this mean?

5) How did the form of this trait change over time? Would you expect that the modern form of the trait evolved quickly with few intermediate steps, or slowly and gradually?

Explanation / Answer

1). Natural selection removes deleterious alleles from a population but it may not happen all the times and in all the cases. There are several possibilities for sustaining genetic disorders that are not removed by natural selection; “balanced polymorphism” is one of the reasons of it.

The inheritance of recessive genes (disease causing) can remain prevalent if presence of two copies of an allele is disadvantageous and presence of one copy of the allele may be advantageous.

For example in case of sickle cell anaemia, two alleles may cause sickle cell anaemia but carrying one allele is advantageous in regions where malaria is common because this single copy of allele offers resistance against malaria. Thus, many people still carry the allele of sickle cell anaemia, as natural selection does not remove it because it is advantageous to the species; this is called “balanced polymorphism.”

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