Course: SAT 170 Introductory Biotechnology

Unit 4 Learning Module

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Figure 10

See Figure 10: A frameshift mutation alters the reading frame of the codons for a particular gene. Notice how the removal of the “g” in the eighth codon alters all of the codons that follow.

Figure 11

Mutations

Permanent changes in DNA sequence are called mutations. They can occur in any cell; if the mutation is present in an egg or a sperm, it can be passed along to offspring. As mentioned in our last unit, these mutations are caused by mutagens which includes certain chemicals and types of radiation. There are several different types of mutations including point mutations, frameshift mutations and chromosomal mutations.

- As you may recall from our last unit, point mutations result when a single nucleotide in the DNA sequence has been changed. Such point mutations can result in any of the following: there may be no change in the protein structure since some amino acids match up with more than one codon, the amino acid sequence may change (missense mutation) or the protein may be greatly truncated due to the presence of an incorrect stop codon (nonsense mutation)
  - Frameshift mutations occur as nucleotides are added or deleted, altering the reading frame of the codons. The severity of the mutation will be primarily determined by where in the reading frame the mutation occurred. For example, frameshift mutations at the beginning of the gene will alter all of the amino acids, while a mutation close to the end may only change a few of the amino acids.
  - Chromosomal mutations involve larger portions of the chromosomes. There are four basic types: deletions, duplications, inversions and translocations. Deletions result in missing pieces of a chromosome, while duplications result in extra copies of a piece of a chromosome. When a chromosome segment is inverted to its mirror image, it is known as an inversion. A translocation occurs when a piece of one chromosome is moved and added to an entirely different chromosome.

See Figure 11: Notice the change in the amount of DNA on the chromosome that undergoes a deletion or insertion. The inversion does not alter the amount of DNA only the orientation of the DNA within the chromosome. Similarly, the translocation does not alter the amount of DNA, but instead causes a change in the location of the DNA to a different chromosome.

The process of gene expression is an important step for organisms to take the genetic information that they have inherited from their parent(s) and convert it into the functional components of their cells. In future units, we will be discussing how researchers take advantage of this physiological process to convert organisms into factories for the production of certain materials.