# Meiosis --- **Meiosis** is the process of [[cell division]] that results in a [[gamete]] that has half the number of [[chromosome|chromosomes]] as the parent cell. In other words, it starts with a [[ploidy|diploid]] cell and ends with four, [[ploidy|haploid]] cells, or gametes. The goal of meiosis is to *vary the genetic make up of the chromosomes as much as possible* while still maintaining a complete [[genome]]. Note: Meiosis does not occur in asexual reproduction, because it does not require gametes. ![[meiosis.png]] Meiosis is divided up into two overarching phases, meiosis I and meiosis II. **[[Meiosis I]]** is where the cells [[homologous pair]] are separated into two daughter cells. As the process is randomized each daughter cell is bound to have some chromosomes from the maternal line and some from the paternal line. In this phase, [[meiosis i#Crossing Over|crossing over]] also introduces variance in the genetic material of the homologues themselves, resulting in completely new, never-before-seen chromosomes. **[[Meiosis II]]** is very similar in process to [[mitosis]]. Th where the now separated and randomized chromosomes have their sister chromatids pulled apart. ## Nondisjunction **Nondisjunction** is a relatively common mistake during meiosis, where one or more of the chromosomes fail to separate and you end up with extra or lacking chromosomes. Nondisjunction in most chromosomes is lethal, but some can be tolerated. For example: [[trisomy 21]] **Mosaicism** ___