Degenerative myelopathy (DM) is a neurological disorder that is occasionally seen in some breeds of dogs. This disease causes a gradual breakdown of muscles and control of movement. Usually, DM is caused by a mutation of the SOD1 gene and is considered a recessive disorder.

dog in adaptive wheelchair for back leg support due to degenerative myelopathy
© handicappedpets1 2009
Creative Commons, CC BY-SA 2.0

Part 1: If two dogs are carriers for DM, describe the probability of genotypes and phenotypes in their offspring. Use a Punnett square to help determine the probability of the possible genotypes and phenotypes in the offspring. Explain your results in paragraph form.
Part 2: Harley has two dogs. One dog has DM and the other dog does not have DM. When these two dogs have puppies, Harley notices that none of the puppies has DM. Explain how Harley can use a test cross to determine the genotype of the parent dog without DM.


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