The cycle is divided into four distinct phases, G1, S, G2, and M (mitosis).
Interphase #
- During interphase, the cell undergoes normal processes while also preparing for cell division.
- For a cell to move from interphase to the mitotic phase, many internal and external conditions must be met.
- The three stages of interphase are called G1, S, and G2.
G1 phase #
- The cell is active and accumulating the building blocks of chromosomal DNA and the associated proteins.
S phase #
- In the S phase (synthesis phase), DNA replication results in the formation of two identical copies of each chromosome (sister chromatids) that are joined by centromere.
- each chromosome is made of two sister chromatids and is a duplicated chromosome. The centrosome is duplicated during the S phase.
- The two centrosomes will give rise to the mitotic spindle.
- Centrioles help organize cell division.
G2 phase #
- the cell replenishes its energy stores and synthesizes the proteins necessary for chromosome manipulation. Some cell organelles are duplicated, and formation of spindle fibres.
- The final preparations for the mitotic phase must be completed before the cell is able to enter the first stage of mitosis.
The mitotic phase #
Mitosis #
Phases
- prophase
- prometaphase
- metaphase
- anaphase
- telophase
Reductional division #
Meiosis is composed of two distinctive cell divisions, meiosis I and meiosis II.
The first division
- there is pairing and recombination between homologous chromosomes resulting in variation in the genetic makeup of the gametes.
- Segregation of the homologues occurs during the first meiotic (reductional) division, reducing the forty-six chromosomes to twenty-three, one from each homologous pair.
The second division
- similar to mitosis with segregation of sister chromatids into daughter cells.
Overview of meiosis. #
The Cell Cycle questions and answers
