Every collie puppy starts out just like Lassie.
To start with, Lassie does not meet the AKC standard for breeding of collies. First, Lassie is much larger than most collies. Breeding to get this exact physical appearance is not an exact science. Collie color charts will tell us what color collie will produce the various coat colors, but it's up to nature whether or not these 4 components all come together. Bob Weatherwax, and his father Rudd, have looked for similar physical characteristics to breed with Lassie when the time comes for a successor to be bred.