Dominant/Recessive Genes

[Mark Joseph Johnston]

I am a computer science student working on genetic algorithms and want to ask
a "silly" question.

Recessive genes are generally not "good" for the organism, yes?
If so why do they exist? Why do two alleles exist together?
Is it to conserve genetic diversity (without manifesting a trait 
with a poor survival value??

Forgive my ignorance.

Cheers.
Mark
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