Final answer:
A mutation can lead to resistance, such as DDT resistance in insects, disorders like Sickle-cell anemia, or new characteristics that are either beneficial or neutral. These genetic changes can affect the organism's fitness and lead to evolutionary changes through natural or sexual selection. The correct option is a.
Step-by-step explanation:
A mutation can lead to various outcomes in an organism, such as resistance, disorder, and new characteristics. For instance, resistance can develop when a mutation causes an allele that confers an advantageous trait, such as the ability to survive exposure to an antibiotic.
An example is the application of DDT, which caused mutations and allowed the allele conferring DDT resistance to appear in certain populations. This illustrates how evolution is an ongoing process, with natural selection favoring beneficial phenotypes.
Disorders can also arise from mutations, particularly when they occur in genes responsible for critical biological processes.
A single-gene mutation may lead to a Mendelian disorder such as Sickle-cell anemia. Despite the disorder, such mutation can simultaneously offer protective advantages against other conditions, like malaria resistance in the case of Sickle-cell anemia. This dual effect is a complex aspect of Mendelian inheritance.
Finally, new characteristics may appear through mutations, which can lead to visible changes in the organism's phenotype. For these new traits to become widespread, they must offer a favorable adaptation, so that the allele reaches a high frequency in the population via natural or sexual selection. Option a. is the correct one.