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Figure 6.7 Types of point mutations with examples.

Figure 6.7 Types of point mutations with examples.

that is being expressed, its complementary DNA strand, the messenger RNA formed from the sequence, and the resulting amino acid sequence.

If the mutation does not leave both strands of the DNA molecule with the proper complementary pair at a point, special repair enzymes can attempt to undo the damage. Of course, the mechanism is not perfect. Sometimes there is so much damage that information is lost. The repair enzymes excise or replace damaged parts of the DNA molecule, but consequently, may leave point mutations.

Mutations have the potential for causing heritable genetic disorders. However, this is less of a concern than the potential for causing cancer. Most heritable genetic disorders are due to genes already in the human gene pool. Some even confer advantages in special situations. For example, sickle-cell anemia, although disabling for those who are double recessive, may give partial immunity from malaria for those who are single recessive. Similarly, it is thought that single-recessive carriers of the cystic fibrosis gene may be relatively resistant to cholera. Nevertheless, exposure to mutagens can increase the frequency of genetic disorders such as those in Table 6.3.

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