In discussion section this week, you will examine the evolution of the genetic code.  Some of the questions
you will be examining are:

    1.  Is the genetic code a "frozen accident"?
    2.  Has the genetic code evolved?
    3.  If so, in what way has it evolved?
 

There are two readings for discussion section this week:
 

    1.  Read the following excerpt from J. Maynard Smith and E. Szathmary,
        The Major Transitions in Evolution (1995; W. H. Freeman).  (Click on image.)
 
 

    2.  Freeland, S. J., and Hurst, L. D.  1998.  The genetic code is one in a million.  J. Mol. Evol. 47: 238-248.
 
 

Assignment:  Write a short (maximum two page) essay on the following question:

        What type of evolutionary process is required for a codon to change the amino acid it specifies?

Hint:  Think about the adverse fitness effects of altering the amino acid specified by a single codon.  How might these adverse effects be mitigated suffiently to allow a change in codon specificity to be favored by natural selection or allowed by
genetic drift?  (Note: this is not a hypothetical question.  These kinds of changes have occurred in some lineages, as described in the reading from Maynard Smith and Szathmary.)

NOTE:  Assignment is due at the beginning of discussion section this week.

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