In what cases is disease only inherited from the mother and only to her sons, and in what cases is disease only inherited from the mother but to both her sons and her daughters?
Use hemophilia and Leber's optic neuropathy as examples.
In diseases inherited from the mother and passed only to the sons, the defective gene is generally on the X chromosome. In females (X-X) there's a normal allele on the other X to balance the disease allele, so they don't show signs of the disease. Since males are X-Y, they don't have this "backup copy" and they'll have the disease if they're carrying a disease allele on their one and only X.
So if you have a normal ...