The most likely explanation is that the mixed race has a low diversity in genes.
Explanation:
Elbow dysplasia is a condition that causes a bad development in the elbows of dogs, causing a bad formation of cartilage in that region of the paw, or a bad structure of the surrounding bones.
This condition is common in mixed breeds, because these breeds have little diversity of genes, allowing this disease to be passed to the offspring during crossbreeding between dogs that already have the disease.
If the mass of one of the objects is doubled, then the force of gravity between them is doubled. Since gravitational force is inversely proportional to the square of the separation distance between the two interacting objects, more separation distance will result in weaker gravitational forces.
