Fertilization is a process that occurs in the method of sexual reproduction.  It requires two parents, one male and one female.  The male parents contributributes a male sex cell, called a sperm, while the female parent contributes a female sex cell, called an ovum, or egg.  Each of the sex cells have a haploid number, or half set, of chromosomes; upon fertilization, the fertilized egg has a diploid, or full set, of choromosomes.  The offspring of sexual reproduction are not genetically identical to either of the two parents, although they inherit all their physical traits from both parents.

Double fertilization occurs among flowering plants.  This is when an ovum, or egg, is fertilized by two male sex cells.  One of the pollen grains delivers a sex cell to the female part of the flower and fertilizes the egg, while another sex cell is delivered and fertilizes two of the polar bodies produced by the female during meiosis.  Meiosis is the process that produces sex cells.