What is the likelihood that a sighted dog carries the gene for blindness if one blind puppy

What is the likelihood that a sighted dog carries the gene for blindness if one blind puppy is born from crossing with the same dog? (normal vision is the dominant sign)

Let’s designate the gene that causes normal vision in dogs as A. Then the gene for canine blindness will be a.

In order for a dog to suffer hereditary blindness, its genotype must look like aa, because homozygosity is an indispensable condition for the realization of the recessive trait of blindness in the phenotype.

To have the aa genotype, a dog must inherit one abnormal gene from the mother and one from the father. Since the parental individuals, according to the condition of the problem, have normal vision, it means that both of them necessarily carry the pathological gene a in a latent, not manifested form as part of the heterozygous genotype Aa.

Answer: 100%.