What is Meiosis?
Meiosis is the process by which gametes, also called sex cells, are made in an organism's reproductive organs.
Most organisms are diploid, meaning they have two copies of each chromosome from paternal and maternal origin. However, their reproductive gametes are haploid, meaning they only have one copy of a chromosome.
In order for reproductive organisms to create the haploid gametes, they must undergo two cycles of meiosis.
Most organisms are diploid, meaning they have two copies of each chromosome from paternal and maternal origin. However, their reproductive gametes are haploid, meaning they only have one copy of a chromosome.
In order for reproductive organisms to create the haploid gametes, they must undergo two cycles of meiosis.
Stages of Meiosis
The process of meiosis involves two divisions, both of which follow the same basic stages as mitosis (prophase, metaphase, anaphase and telophase)
Meiosis is preceded by interphase, which includes the replication of DNA (S phase) to create chromosomes with genetically identical sister chromatids |
Meiosis I Meiosis II
Prophase I* Prophase II Anaphase I Anaphase II Metaphase I Metaphase II Telophase I Telophase II Cytokinesis Cytokinesis |
Process of Meiosis
As a result of meiosis (including crossing over) four genetically distinct haploid gametes have been created.
Crossing Over*
Crossing over is a process that only occurs once during Meiosis, during Prophase I.The process of crossing over occurs as follows:
- Homologous chromosomes become connected in a process called synapsis, forming a bivalent (or tetrad)
- Non-sister chromatids break and recombine with their homologous partner, effectively exchanging genetic material (crossing over)
- The non-sister chromatids remain connected in an X-shaped structure and the positions of attachment are called chiasmata