Final answer:
Humans are the species naturally affected by Leber's congenital amaurosis II, which led to gene therapy development. This condition causes blindness at birth due to genetic mutations, and gene therapy offers a potential cure by fixing the genetic defect.
Step-by-step explanation:
The species naturally affected by Leber's congenital amaurosis II that led to the development of gene therapy is d) Humans. Leber's congenital amaurosis II is a genetic condition primarily affecting humans, particularly involving a severe loss of vision or blindness at birth. This genetic disorder is caused by mutations in various genes necessary for the function of photoreceptors in the retina. Due to the nature of the condition stemming from genetic mutations, traditional treatments are oftentimes ineffective.
Gene therapy has been explored as a potential treatment option because it involves correcting the underlying genetic defects that cause the disease. This therapeutic approach includes the introduction of a correct version of the affected gene into the patient's cells using a viral vector. While this type of gene therapy was initially tested on animals like mice, it has been developed to treat human patients with Leber's congenital amaurosis.