The The cell starts to divide. Meiosis

The stages of mitosis – that process that allows cells to divide and reproduce – are detailed and complex. Learn about the ins and outs of telophase, the final step of mitosis. Learn also about telophase I and telophase II, the final stages of each half of meiosis.

Telophase

Telophase is the final stage of mitosis, or the process by which cells divide.

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Mitosis consists of five phases – prophase, prometaphase, metaphase, anaphase, and telophase. During telophase, the nuclei for the daughter cells finally form and the cell begins to split into two.Meiosis is the process that leads to the formation of sperm cells and egg cells.

The same five phases that are in mitosis occur twice during meiosis. In this lesson we will also talk about telophase I and telophase II.

The Cell Cycle

Before going into the specifics of mitosis and telophase, let’s first examine the life span of a eukaryotic cell, which is called the cell cycle. A cell spends the bulk of the cell cycle in interphase.

During interphase, the cell grows (G1), replicates its DNA through DNA synthesis (S) and grows again (G2) until it is ready to divide. Then the cell undergoes mitosis, after which it divides by cytokinesis.

The cell cycle, showing the three steps of interphase, plus mitosis and cytokinesis.
Cell Cycle

The S phase is special because during this time the cell must double its DNA. This doubling ensures that when the cell divides into two, each daughter cell will receive the full DNA of the parent.

The daughter cells have the same number of chromosomes (DNA) as the parent cell originally had.

Mother Daughter cells

Mitosis

Mitosis is the most important part of cell division because it is the process by which the parent cell gives its DNA to its two daughter cells. Mitosis is an asexual form of reproduction. In single-celled organisms, it makes two offspring that are genetically identical to the parent. In multicellular organisms, mitosis is responsible for growth and tissue repair. It is also the process by which a fertilized egg grows into a newborn.

What mitosis does not do is to make either sperm cells or egg cells; that process is called meiosis.

Mitosis, combined with cell division, is how many single-celled organisms like the Amoeba reproduce.
Amoeba Dividing

Five Stages

As we just mentioned, there are five stages of mitosis. Prophase is when mitosis begins. Chromatin turns into chromosomes, with sister chromatids joined together. The nuclear membrane begins to dissolve and the mitotic spindle begins to form.

During prometaphase, the mitotic spindle formation is completed. The chromatids begin to move toward the center of the cell and the nuclear membrane disappears.Chromatids line up along the metaphase plate at the cell’s equator during metaphase.During anaphase, the chromatids split and each daughter chromosome moves towards its own pole of the cell. The cell also elongates.During telophase, the cell continues to elongate.

The nuclear membranes form around the daughter chromosomes, forming distinct nuclei, and the mitotic spindle disappears. At this point, mitosis ends.

The last stage of Interphase, followed by the stages of mitosis.
Mitosis

Cytokinesis is the final stage of the cell cycle. In animal cells, the cell is pinched in the middle until two daughter cells are formed. The cell cycle begins anew.

In plant cells, a new division of the cell wall separates the daughter cells, which remain adjacent.

Telophase

Telophase marks the end of mitosis. By this time, a copy of each chromosome has migrated to each pole. These chromosomes are surrounded by a nuclear membrane that forms at each pole of the cell while the cell is pinched in the middle (for animals) or divided by a cell plate (for plants).

Telophase. The nuclear envelopes form at each pole of the cell.

The spindle disappears. The cell starts to divide.

Telophase

Meiosis Phases

Meiosis is the process by which sperm cells and egg cells are formed. As such, it is involved in sexual reproduction. A primary spermatocyte undergoes meiosis to give rise to four genetically distinct sperm cells. A primary oocyte undergoes meiosis to give rise to one egg cell and three genetically distinct polar bodies.

A polar body is a tiny, non-functional cell that contains little besides a nucleus with a unique blend of DNA.

Meiosis involves two cell divisions. Each daughter cell, whether sperm or polar body, has 1/2 the DNA of the parent cell.
Meiosis

The phases of meiosis are generally the same as mitosis. However, the phases are completed twice and thus have a roman numeral after each phase. Prophase I is when meiosis begins.

The chromatin turns into chromosomes and the first sister chromatids form. Then homologous chromatids join together to form tetrads. Crossing-over occurs as DNA is exchanged between homologous chromosomes. The nuclear membrane dissolves, and the mitotic spindle forms.

During metaphase I, tetrads line up along the metaphase plate at the cell’s equator. Homologous sister chromatids split.Anaphase I is when the homologous sister chromatids move toward opposite poles of the cell. The cell also elongates.During telophase I, the cell continues to elongate and the mitotic spindle disappears. Then cytokinesis occurs. Everything that happens from now on occurs in both daughter cells.

During prophase II, the mitotic spindle reforms and the chromatids begin to move toward the center of each cell.The chromatids line up at cell’s equator during metaphase II.During anaphase II, the chromatids split and chromosomes move toward opposite poles of the cell.Finally, during telophase II, the cell continues to elongate. The nuclear membranes form around the chromosomes as cytokinesis divides each cell in two.

Each of the four daughter cells (2 from each cell) has a unique complement of DNA. The mitotic spindle disappears and meosis ends.

Meiosis involves two cell divisions but only one DNA replication. Daughter cells do not have identical DNA.
Meiosis

Telophase I & Telophase II

By now, the tetrads have split into separate chromatids, but the chromatids have not yet split into separate chromosomes.

That won’t happen until anaphase II. At the end of telophase I the still-intact chromatids are at both poles of the cell. The cell then undergoes cytokinesis, forming two 1N daughter cells. In sexually reproducing organisms, 2N means that the cell has DNA from both parents (homologous pairs of chromosomes), and 1N means that the cell has DNA from only one parent.

It is worth noting that even though each chromosome is doubled in a chromatid, it’s still a 1N cell; the homologous chromosomes are in different daughter cells.At the end of cytokinesis, the cells will either begin prophase II right away or will form nuclei and enter an extra interphase state, depending on the species. DNA is never replicated during this version of interphase.Telophase II is the time when each daughter cell from meiosis I is starting to split, signaling the end of meiosis II. This time, nuclear membranes form around the 1N nuclei before cytokinesis starts.

The resultant cells are either four genetically distinct sperm (male meiosis) or a single, viable egg cell with three polar bodies, all genetically distinct (female).

Four sperm with genetically distinct 1N nuclei result from male meiosis.
Spermatogenesis
While only one functional egg cell result from female meiosis, there are three polar bodies that contain the extra DNA. All are 1N and genetically distinct.
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