Mutations Could Cause Little Effect or Severely Debilitate Gene Function

With the determination of the base sequence of the human genome, research is turning more towards genetic variation. Every normal human genome is unique in that no two people are exactly alike. Genetic variation also includes incidental changes that result in mutation or genetic mistakes. The mutation of a single base may have no effect on the protein product of an expressed gene. However, a single mutation can lead to the production of a protein completely different from the necessary protein. These mutations can have detrimental results.

Single Base Changes in the Gene: Substitution

The human genome consists of 3 billion repeating bases designated as A, G, C or T. The combination of 3 bases, a codon, determines what amino acid that will be added to a protein chain. This calculates to a total of 64 possible 3 base combinations that represent the 20 amino acids forming a protein molecule. Therefore, certain amino acids are represented by more than one codon. One example of an amino acid is Serine. The codes for Serine include TCT, TCC, TCA, and TCG. A mutation in the third base of the codon for Serine does not effect the formulation of the protein. It should be noted that Serine is also coded with AGT and AGC. Mutation that results in the third base to A or G would change the amino acid expressed by the gene to Arginine. This may or may not affect the protein.

Mutations are not Limited to Substitution

Mutations that can have more profound effects on gene expression are the result of the insertion or deletion of single or multiple bases. This is called an indel, which stands for insertion-deletion. The effects of an indel cause change by shifting the entire code of the gene, also known as a frameshift, resulting in the formation of a completely different protein. An example of this is an indel's affect on the DNA sequence TTC-CCC-AGC-GAC. This codes the four amino acids Phenaline-Proline-Serine-Asperine. If one base is deleted from the DNA code giving TCC-CCA-GCG-ACX, then the amino acids coded are Serine-Proline-Alanine-Thromine. The resulting protein may provide no useful function.

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