What breeder inbred them.
The different breeds were essentially
created by inbreeding. And losing those attributes is one of the biggest reasons for breed degradation.
Inbreeding was used to enhance specific characteristics, and was a way to limit genetic variation (normally we consider genetic variation to be a good thing, but when you're trying to create a breed of dogs that differ from one another very little, genetic variation is a detriment).
To create a breed of dog, you essentially pick out an animal that has attributes you like (color, size, temperament, whatever...), and breed it with an animal that is as close to your initial "ideal" animal as possible. You then take the off-spring and compare them to the original animal.
Now, the offspring are only 50% of the original "ideal" animal... Those attributes you liked so much are diluted by the mate you chose for your ideal animal...
So, you now take the "best" of the offspring (the one closest in attributes to your original ideal) and breed it back with the original "ideal" animal. You breed the mother with her son...
Now look the offspring over again, and pick out the one closest to the original ideal. That offspring is now 75% of the original "ideal", so you're getting closer to your goal... Breed the mother with her grandson, and then with her great-grandson, and repeat and repeat and repeat...
Now, of course you will enhance the attributes you're looking for, but will also enhance attributes you
don't want. Those animals that show attributes you
aren't trying to enhance would generally be "culled". Nowadays, we'd hopefully not allow them to breed; historically they probably just did away with them.
Without that careful inbreeding we wouldn't have the different breeds of domestic dog that we have nowadays.
Kind of puts the "Hitler-istic" comments made earlier in a different light.
