Final answer:
The claim that mutations in CYP2D6 increase tamoxifen toxicity is false; instead, they may affect the drug's efficacy. Not all mutations are harmful or caused by toxic substances, and they can lead to both beneficial and detrimental effects.
Step-by-step explanation:
The statement that mutations in CYP2D6 increase tamoxifen toxicity is false. The Cytochrome P450 2D6 (CYP2D6) enzyme is involved in the metabolism of tamoxifen, a medication used in the treatment of breast cancer. Variations or mutations in the CYP2D6 gene can lead to different metabolizer phenotypes. Poor metabolizers with certain CYP2D6 mutations may have decreased ability to convert tamoxifen into its active metabolites, potentially reducing efficacy rather than increasing toxicity. In fact, patients with these mutations may require alternative treatments.
Regarding mutations in general, they can be beneficial, harmful, or neutral. A beneficial mutation might provide a survival advantage, such as increased resistance to a disease, while a harmful mutation could lead to a genetic disorder or increased susceptibility to environmental dangers. For instance, the mutation giving rise to sickle cell anemia can be harmful by causing the condition, yet it can also be beneficial by providing resistance against malaria.
Exposure to mutagens, such as cigarette smoke, can cause cancer because these substances contain chemicals that can damage DNA, leading to mutations that disrupt normal cell growth and division. Not all mutations are caused by exposure to toxic substances; some occur as random errors during DNA replication. Also, some mutations can indeed make chromosomes longer or shorter, altering the structure and number of genes present, which can affect an organism's traits and functions.