8. What is the difference between a linkage map and a physical map? (A) For a linkage map, markers are spaced by recombination frequency, whereas for a physical map they are spaced by numbers of base pairs (bp). (B) For a physical map, the ATCG order and sequence must be achieved, but not for the linkage map. (C) For a linkage map, it is shown how each gene is linked to every other gene. (D) For a physical map, the distances must be calculable in units such as nanometers. (E) There is no difference between the two except in the type of pictorial representation.