Duchenne muscular dystrophy is an x-linked recessive disorder. Victims of the disease become progressively weaker, starting early in life. If your father's brother had the disorder (but your father is unaffected), what is the probability that you have received an affected allele from your father?

As the father is unaffected there is zero chance you would have an affected allele. Assuming normal male genotype for your father he has only one X and a Y. If his X was affected then he would have DMD. Because you need at least one healthy X copy to make you affected and makes only have one X it greatly increases their risk of DMD