Cells need both genes, and each cell inherits half of the genes from both cell parents.
Mitochondria is a semi autonomous cell organelle, it is able to make its own protein because it has promiscuous DNA which has genes that have instructions to make proteins
In hemophilia A it’s caused by a mutation in the gene for factor VIII. Hemophilia B is a result in a deficiency in factor IX due to a mutation in its corresponding gene.
In both cases, it is a mutation in the DNA (the macromolecule).