How Was It First Determined That Genetic Material Got Combined

How was it first determined that genetic material got combined when eggs and sperm fused?

A) It was observed that when sea urchin eggs and sperm fused, the cell nuclei fused as well, meaning the genetic material was combined.
B) The gene sequence in newly hatched nematodes was compared to that of the parent and determined to be a mixture.
C) The quantity of genetic material in a sperm and egg cell was compared to that of a fertilized egg, and the fertilized egg contained twice as much, meaning it had come from both the sperm and the egg.
D) The traits of any offspring are a mixture of the traits of its parents.
E) The genes in a frog egg and sperm cell were counted and added up, and then the genes were counted in a fertilized frog egg, and the numbers were equal.