What is the edwards syndrome mode of inheritance?

Sporadic event. The preparation of an egg for fertilization includes reducing all the chromosomes (22 regular pairs + a sex chm pair) from pairs to singles. The sperm then brings a single 1-22 regular +a sex chromosome. If the egg has a pair of 18 chms, then when the sperm adds the single 18 there is 3, this creates the chms imbalance in every skin cell of the fetus & results in the defects of edward syndrome.