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Genotype Versus Phenotype

by Greg Crowther


I'll start this by noting
That genes encode proteins,
Which dictate cell function and form.
So if a gene mutates,
The cell may gain new traits
Far better or worse than the norm.

Genotype -- ooh...
It's the genes you possess;
Nothing more, nothing less --
Versus phenotype -- ooh...
Your appearance and health
And reproductive success.

In some situations,
There is a mutation,
Yet phenotype stays just the same.
So guessing the genotype
Just from the phenotype
Can be a difficult game.



The distinction between genotype and phenotype can be confusing to introductory biology students. This song was written as a study aid for these students -- specifically, the students in Biological Frameworks for Engineers at the University of Washington (ChemE 355/599 and EE 400/546).

Questions: (1) Why might a genotype change (mutate)? (2) What general kinds of changes in genotype are more likely and less likely to cause changes in phenotype? Answers: (1) Mutations generally arise from incorrect copying or repair of DNA bases, such that the usual complementarity (A goes with T, and C goes with G) is violated. Mutations can happen spontaneously, but their frequency can be increased by radiation, chemicals, pieces of mobile DNA (viral or otherwise) that jump around the genome, mutations in DNA-checking enzymes, etc. (2) Single-nucleotide polymorphisms often have no effect on phenotype, as they usually change only one amino acid in the protein or none at all. Frameshift mutations, in which bases are added or deleted, usually lead to premature stop codons and truncated proteins with altered functions, and thus altered phenotypes.

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