Genetic Mutation

1. Discuss the three different types of gene mutations discussed in the commentary: Week 6–Gene Mutations and DNA Repair. Describe in detail how insertion, deletion, and base substitution of nucleotides can have a significant impact on genes. Find three specific examples (actual gene mutations, not chromosome mutations) of ways in which a very small change in DNA can have a major impact on an organism, and describe each mutation in detail.

Three types of gene mutations are base substitution, deletion and insertion. These three types occur at the gene level and not at the chromosome level and can occur from an error in DNA replication or from environmental factors such as x-rays, UV radiation or toxic chemicals. These environmental factors that can cause mutations are called mutagens.

Usually, the least harmful of these gene mutations is the base substitution because it only affects a single triplet or codon. In a base substitution one base is exchanged for another base. The change in base could have no effect on the coded protein, in which case the mutation is known as a silent mutation because there is no noticeable effect. If the change in the codon causes a stop code, the protein will be terminated at that point and may be useless. This is called a nonsense mutation. If the change leads to a code for a different amino acid the resulting protein may not be affected or may be greatly affected and this is called a missense mutation.

An example of a substitution mutation that can cause a severe condition is sickle cell disease. In sickle cell disease, a substitution mutation occurs on the HBB gene which codes for beta-globin, a subunit of hemoglobin. The point mutation in sickle cell disease is a substitution of a codon that causes the gene to code for a different version of beta-globin, which in turn causes the production of red blood cells that are sickle shaped. Sickle cell disease is an autosomal recessive disease. If a person has only one of the...