What action should a person with sickle cell anemia take to prevent a sickling crisis?

Choice A reason: Cell-mediated immunity, part of adaptive immunity, targets specific pathogens after exposure, not species-specific barriers. It is not the primary defense against cross-species transmission, making this choice incorrect for species-specific immunity.

Choice B reason: Natural immunity is a vague term, often meaning innate or acquired immunity. It is not specifically species-specific, as innate immunity provides the primary barrier to zoonotic diseases, making this choice incorrect.

Choice C reason: Acquired immunity develops after exposure or vaccination, targeting specific pathogens. It is not species-specific and does not primarily prevent animal-to-human disease spread, making this choice incorrect.

Choice D reason: Innate immunity, including species-specific barriers like skin and mucosal defenses, prevents pathogen transmission across species. These non-specific mechanisms reduce zoonotic disease risk, making this the correct choice for species-specific immunity.

Choice A reason: Autosomal dominant disorders affect both genders equally, as they are not sex-linked. Heterozygous individuals express the disorder, not just males, due to the dominant allele on an autosome. The idea of females being carriers only applies to X-linked recessive disorders, making this choice scientifically inaccurate.

Choice B reason: Autosomal dominant disorders are caused by mutations on autosomes, not the Y chromosome, which is sex-linked and primarily affects males. These disorders do not typically skip generations, as the dominant allele is expressed in every affected individual, making this choice incorrect.

Choice C reason: In autosomal dominant disorders, a single mutated allele is sufficient for expression. An affected parent (heterozygous) has one normal and one mutated allele, leading to a 50% chance of passing the mutated allele to each child, causing the disorder. This genetic inheritance pattern makes this the correct choice.

Choice D reason: In autosomal dominant disorders, there is no "carrier" state as in recessive disorders, because heterozygous individuals express the disorder. The 50% probability applies to inheriting the disorder itself, not a carrier genotype, which is a concept relevant to autosomal recessive disorders, making this choice incorrect.