Answer:
c. Affected fathers have all affected daughters, but no affected sons.
Explanation:
Given that the disease is caused by a dominant allele on X chromosome, an affected father would have a disease allele in the X chromosome that passes along to the male gamete, while the gametes containing a Y chromosome would not have it (since it is X-linked).
During sexual reproduction, the father passes an X chromosome to its daughters (the second X chromosome being contributed by the mother) but an Y chromosome to its sons (the single X chromosome being contributed by the mother).
Indeed, within an affected father's offspring, all his daughters will receive the affected X chromosome from him, while his sons will receive an unaffected Y chromosome (since the disease is X-linked). These males will not inherit the disease, for they will receive an unaffected X chromosome from her mother (which is expected to be healthy since the disease is rare).
