Final answer:
The statement that genetic mutations are always harmful is 2) false. Mutations can be beneficial, harmful, or neutral, and not all mutations are caused by exposure to toxic substances. Some mutations can also change the length of chromosomes.
Step-by-step explanation:
The statement that genetic mutations are always harmful is false. While it is true that many mutations can be detrimental, leading to genetic disorders or cancer, this is not always the case. In fact, mutations can be beneficial, harmful, or even neutral with no effect on the organism.
An example of a beneficial mutation is the one that conferred resistance to insecticides in mosquitoes, improving their survival chances. On the other hand, a well-known example of a harmful mutation is the one that causes sickle-cell disease, a serious genetic disorder. It is important to understand that exposure to mutagens, such as cigarette smoke, can damage DNA and cause mutations that lead to cancer.
Moreover, mutations are not always caused by exposure to toxic substances; they can also occur naturally during DNA replication. Furthermore, some mutations can indeed result in changes to the length of chromosomes, making them either longer or shorter.