By name or number, identify all of the following statements related to linking numbers that are true. 1) The specific linking difference is calculated with respect to the specific length of the DNA molecule being analyzed 2) Linking number is calculated as the difference between its writhe and twist components 3) The superhelical density in cellular DNA is typically around –0.06 4) The writhe component of linking number may be interpreted as the measure of the coiling of the DNA helix axis