If I had unlimited time and unlimited resources, could I take a population of 100 pure-bred German Shepherd Dogs and selectively breed them until I came up with a Cocker Spaniel?
I obviously meant “breeding,” not “breedimg.”
Theoretically, you could take a population of 100 pure bred lions and get a cocker spaniel, given an infinite amount of time, and assuming 100% control conditions.
That being said, the odds of random genetic material (that’s already occurred), occurring again, perfectly, is astronomically unlikely.
No, you couldn’t “selectively breed” from 100 German Shepherds to get to Cocker Spaniels, because that assumes that there is a range of genetic variation already available in German Shepherds that can be selected to yield the characteristics of Cocker Spaniels. Undoubtedly, some of the characters of Cocker Spaniels are due to genetic variants (alleles) that are present in Spaniels but not Shepherds. Since both are pure breeds, they are going to be homozygous (have the same version of an allele) at most genetic loci that are significant for determining the breed.
Now given infinite time, you could eventually get to Cocker Spaniels, but you would have to wait until the proper mutations occurred in your population of Shepherds. But assuming you have a fixed population size of 100, it will take you pretty near an infinite amount of time until those mutations occur.
You could, however, get something very closely resembling a Cocker Spaniel by starting from a population of wolves (after all, it’s been done before). Wild-type wolves, though, have far greater genetic diversity than any pure breed.
True. But even so, you would want to select from a population of larger than 100 individuals, at least at the early stages.