a fertilized egg is formed by a sperm and an egg cell fusing together
fertilization is enrichment. external_fertilization is egg_fertilization. stratifying is reproductive_fertilization. self_fertilization is fertilization. stratifying is not reproductive_fertilization. egg_fertilization is not reproductive_fertilization. fertilization is creation. egg_fertilization is reproductive_fertilization. fertilization is not creation. external_fertilization is not egg_fertilization.