Cell Cycle and Mitosis Quiz

Study Notes

The cell cycle is a series of events that take place in a cell leading to its division and duplication.
Interphase is the longest phase of the cell cycle, taking up 95% of the cell's time.
M-phase is the shortest phase and includes both mitosis and meiosis.

Mitosis is a type of cell division that results in two daughter cells that are genetically identical to the parent cell.
It's also known as equational division as the chromosome number remains the same.
Karyokinesis refers to nuclear division, while cytokinesis refers to cell division.

Prophase: Chromatin condenses into chromosomes, centromeres move to opposite poles, and the mitotic apparatus (aster and spindle fibers) appears.
Metaphase: The chromosomes are aligned at the metaphase plate (equator of the cell), and centromeres of chromosomes are attached to spindle fibers.
Anaphase: Centromeres split and sister chromatids move to opposite poles of the cell.
Telophase: Chromosomes decondense, nuclear envelope reforms, and cytoplasm divides.

Cytokinesis occurs after mitosis and is the division of the cytoplasm, resulting in two distinct daughter cells.
In animal cells, cytokinesis occurs through furrow formation, while in plant cells, it occurs through cell plate formation.

The G0 phase is a quiescent stage where cells are metabolically active but do not divide.
Examples of cells in the G0 phase include red blood cells and heart cells.

Syncytium is a multinucleate condition that arises due to karyokinesis without cytokinesis.
The liquid endosperm of a coconut is an example of a syncytium.

Meiosis is a type of cell division that produces gametes (sperm and egg cells) It's a reduction division, where the chromosome number is halved.

Prophase I: This is the longest phase of Meiosis I, and it comprises five sub-stages:
- Leptotene: Chromosomes condense and become visible.
- Zygotene: Homologous chromosomes pair up in a process called synapsis. The synaptonemal complex is formed, and the paired chromosomes are called bivalents.
- Pachytene: Crossing over occurs between non-sister chromatids of homologous chromosomes, leading to genetic recombination. The bivalents become more visible, and recombination nodules appear.
- Diplotene: The synaptonemal complex dissolves, and the homologous chromosomes begin to separate. Chiasmata, the points of cross-over, become visible.
- Diakinesis: The chromosomes further condense, chiasmata move towards the ends of chromosomes (terminalization), and the nucleolus disappears.
- Metaphase I: The paired homologous chromosomes line up at the metaphase plate.
- Anaphase I: Homologous chromosomes separate and move to opposite poles of the cell.
- Telophase I: The chromosomes reach the poles, and the nuclear envelope reforms. Cytoplasm divides, and two daughter cells are formed.
- Interkinesis: It’s the short interphase between meiosis I and meiosis II. No DNA replication occurs during this phase.

Meiosis II is similar to mitosis, but it involves the separation of sister chromatids. It occurs in the two daughter cells produced by meiosis I.
It is important to remember that crossing over occurs during prophase I of meiosis I and is an essential process for genetic recombination.
Recombinase is the enzyme responsible for crossing over, and chiasmata are the X-shaped structures that represent the points of cross-over.
In some vertebrate oocytes, the diplotene stage of prophase I can last for months or even years.