The founding of the breed - the Gene Pool
Let's pretend these 11 dogs are the "founders" of your breed - they are the first dogs entered into the studbook. All subsequent members of the breed are descended from these dogs only. The breed has a closed gene pool.
All of the genetic variability that will ever exist in your new breed is present in these dogs. Mutations probably won't add new genetic variation because most mutations cause functional problems and get weeded out. So, unless additional "founders" are added to the population at a later date, all of the genes you will ever have to work with in your breeding program are present in these dogs.
In each of these dogs there are at least a few (and perhaps many) recessive genes that could cause genetic disorders. But these disorders will only expressed if a dog is homozygous for the disease allele - it must have TWO copies, one from each parent. As long as the disease genes are rare in the population, very few animals will ever display the illness.
All of the genetic variability that will ever exist in your new breed is present in these dogs. Mutations probably won't add new genetic variation because most mutations cause functional problems and get weeded out. So, unless additional "founders" are added to the population at a later date, all of the genes you will ever have to work with in your breeding program are present in these dogs.
In each of these dogs there are at least a few (and perhaps many) recessive genes that could cause genetic disorders. But these disorders will only expressed if a dog is homozygous for the disease allele - it must have TWO copies, one from each parent. As long as the disease genes are rare in the population, very few animals will ever display the illness.
Can the gene pool get bigger? (No!)
Okay, starting with your 11 founder dogs, let's let them reproduce. To keep it simple, we will let them produce only identical copies of themselves - clones.
Now we have 27 dogs, all of which are exact copies of one of the founders. What has happened to the size of the gene pool?
Nothing.
You now have more dogs, and you now have more copies of the genes found in the dogs that had more offspring, like that busy gray dog with the red tongue. So, the frequency of particular alleles is different in this population than in the founders, but the number of different alleles in the population is exactly the same. (We're ignoring the possibility of a mutation fort now.)
What if the dogs reproduce normally instead of producing clones? In sexual reproduction, each puppy receives one set of genes from each parent. Different puppies receive a different mix of genes from its parents, so each one is a bit different. Also, each parent dog has a different number of offspring and might mate multiple times with different dogs. So the frequency of the various alleles in the population could be very different in this new population than in the founders.
But again, even though there are now more dogs in the population, the gene pool does not get bigger.
In fact, it doesn't matter how large this breed gets - it might someday grow to thousands of dogs - but as long as the stud book is closed, the gene pool will never be larger than it is when the breed is founded.
Now we have 27 dogs, all of which are exact copies of one of the founders. What has happened to the size of the gene pool?
Nothing.
You now have more dogs, and you now have more copies of the genes found in the dogs that had more offspring, like that busy gray dog with the red tongue. So, the frequency of particular alleles is different in this population than in the founders, but the number of different alleles in the population is exactly the same. (We're ignoring the possibility of a mutation fort now.)
What if the dogs reproduce normally instead of producing clones? In sexual reproduction, each puppy receives one set of genes from each parent. Different puppies receive a different mix of genes from its parents, so each one is a bit different. Also, each parent dog has a different number of offspring and might mate multiple times with different dogs. So the frequency of the various alleles in the population could be very different in this new population than in the founders.
But again, even though there are now more dogs in the population, the gene pool does not get bigger.
In fact, it doesn't matter how large this breed gets - it might someday grow to thousands of dogs - but as long as the stud book is closed, the gene pool will never be larger than it is when the breed is founded.
Can the gene pool get smaller? (Yes!)
The gene pool of a closed breed can never get bigger. But it can get smaller.
What if breeders didn't like black ears, so all the puppies with black ears were spayed or neutered and sent to pet homes? If
We see here that none of the dogs in this population have black ears. In fact, the alleles that produce black ears are completely absent in this population. How can this happen?
1) Dogs with black ears were selected against, so the absence of black-eared dogs is deliberate; or
2) some other trait was selected against that also resulted in the loss of black ears, so the loss of black ears was unintentional.
How can you unintentionally lose a trait by selecting for or against something else?
What if breeders didn't like black ears, so all the puppies with black ears were spayed or neutered and sent to pet homes? If
We see here that none of the dogs in this population have black ears. In fact, the alleles that produce black ears are completely absent in this population. How can this happen?
1) Dogs with black ears were selected against, so the absence of black-eared dogs is deliberate; or
2) some other trait was selected against that also resulted in the loss of black ears, so the loss of black ears was unintentional.
How can you unintentionally lose a trait by selecting for or against something else?
The genes for different traits might not be independent
