In some breeds of dogs, a dominant gene B controls the trait of barking. If a breeder wants to produce a true-breeding strain of barkers, but knows that the allele for silent dogs (b) is present amongst the barking dogs in his kennels, how could he determine which of his barking dogs to breed? Please perform a testcross using a homozygous recessive silent dog (bb).
To determine which of the barking dogs to breed in order to produce a true-breeding strain of barkers, the breeder can perform a testcross using a homozygous recessive silent dog (bb). This testcross involves breeding each of the barking dogs with the homozygous recessive silent dog.
Here are the steps to perform the testcross:
1. Identify the barking dogs that are potentially heterozygous for the barking trait (Bb). These dogs may carry the allele for silent dogs (b) in addition to the dominant barking allele (B). It's important to note that the dogs that are already known to be homozygous dominant (BB) should not be included in the testcross, as they will always produce barking offspring.
2. Select a homozygous recessive silent dog (bb) from the kennels. This dog will always carry the allele for silent dogs and will serve as the testcross parent.
3. Breed each of the potentially heterozygous barking dogs (Bb) with the homozygous recessive silent dog (bb). This will produce offspring that can help in determining the genotype of the barking dogs.
4. Observe the offspring carefully. If any offspring from a barking dog and the silent dog (bb) are silent (barkless), it means that the barking dog is heterozygous (Bb) for the barking trait. On the other hand, if all the offspring from a barking dog and the silent dog (bb) are barking (not barkless), it means that the barking dog is homozygous dominant (BB) for the barking trait.
5. Based on the results of the testcross, select the barking dogs that are found to be homozygous dominant (BB) for breeding. These dogs will produce true-breeding strains of barkers, as they will always pass on the dominant allele for barking to their offspring.
Repeat the testcross process for other potentially heterozygous barking dogs and continue selecting homozygous dominant (BB) dogs for breeding to establish a true-breeding strain of barkers.
By performing the testcross using the homozygous recessive silent dog (bb), the breeder will be able to identify which of the barking dogs are homozygous dominant (BB) and are suitable for breeding to produce a true-breeding strain of barkers.