Originally Posted by Zoom
The biggest fault of all is "lethal white", which we're all fairly familiar with. It happens when two merle dogs are bred together, producing a MxM dog. These dogs typically have sight and hearing issues, total deafness being very common as well as the lack of properly formed irises and in some severe cases, a total lack of eyeball. Dogs with an excessive amount of white should not automatically be classified as "LW".
Same problem persists in Border Collies... and in fact in any breed with a merle gene, AFAIK. Harlequin Great Danes have the same problem.