Dominance of suppressor mutations

Whether or not a suppressor mutation is dominant or recessive to the wild-type gene depends upon if the phenotype is due to a gain of function mutation (e.g. an alteration in a tRNA allowing it to recognize a nonsense codon) or a loss of function mutation (e.g. increased expression of a leaky gene product due to loss of a negative regulator). Several examples are shown below:

A question to ponder: A mutation that results in an unstable protein may be suppressed by a second mutation that inactivates a protease. Would the suppressor mutation be dominant or recessive to the wild-type protease?

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Last modified September 18, 2001