Editing Fertilisation (section)

== Fertilisation and genetic recombination ==
[[Meiosis]] results in a random segregation of the genes that each parent contributes. Each parent organism is usually identical save for a fraction of their genes; each [[gamete]] is therefore genetically unique.  At fertilisation, parental [[chromosome]]s combine. In [[human]]s, (2²²)² = 17.6x10<sup>12</sup> chromosomally different [[zygote]]s are possible for the non-sex chromosomes, even assuming no [[chromosomal crossover]].  If crossover occurs once, then on average (4²²)² = 309x10<sup>24</sup> genetically different zygotes are possible for every couple, not considering that crossover events can take place at most points along each chromosome.  The X and Y chromosomes undergo no crossover events{{citation needed|date=April 2015}} and are therefore excluded from the calculation.  The [[mitochondrial DNA]] is only inherited from the maternal parent.