In some breeds of dogs, a dominant gene controls the characteristic of barking while trailing. In these dogs, another independent gene produces erect ears; it is dominant of its allele for drooping ears. Suppose a dog breeder wants to produce a pure-breeding strain of droop-eared barkers, but he knows that the genes for silent trailing and erect ears are present in his kennels. How should he proceed?
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To produce a pure-breeding strain of droop-eared barkers, the dog breeder needs to carefully select and breed dogs that have the desired characteristics. In this case, the desired characteristics are drooping ears and barking while trailing.
Since the genes for silent trailing and erect ears are present in the kennels, the breeder needs to identify dogs that possess the alleles for drooping ears and the ability to bark while trailing, and then selectively breed them together.
To do this, the breeder should follow these steps:
1. Identify dogs that have drooping ears: Unlike erect ears, drooping ears are recessive, meaning a dog must have two copies of the allele for drooping ears to exhibit this characteristic. By observing the physical appearance of the dogs in the kennel, the breeder can identify the dogs with drooping ears.
2. Identify dogs that can bark while trailing: This characteristic is controlled by a dominant gene. Therefore, any dog that barks while trailing must have at least one copy of the dominant allele for this trait. The breeder can simply observe the behavior of the dogs when they are trailing to identify those that exhibit barking behavior.
3. Select dogs with both desired traits: Identify dogs that possess both drooping ears and the ability to bark while trailing. These dogs will have two copies of the recessive allele for drooping ears and at least one copy of the dominant allele for barking while trailing.
4. Breed the selected dogs: Mate the dogs that possess both desired traits together. By doing so, the breeder increases the likelihood of producing offspring with the same traits. Over multiple generations of selective breeding, the desired traits will become more and more prevalent within the breeding strain.
5. Continuously assess and refine the breeding program: Monitor the offspring to ensure that they exhibit the desired traits. If any dogs in the new generation do not have drooping ears or the ability to bark while trailing, they should not be bred and should be removed from the breeding program.
By following these steps and continually selecting and breeding dogs with the desired traits, the breeder can eventually produce a pure-breeding strain of droop-eared barkers.