When do chromosomes duplicate in meiosis

In particular, two structures called centrosomes move to opposite sides of the cell during this phase and begin building the mitotic spindle. The mitotic spindle plays a critical role during the later phases of mitosis as it orchestrates the movement of sister chromatids to opposite poles of the cell Figure 2.

After prophase is complete, the cell enters prometaphase. During prometaphase, the nuclear membrane disintegrates and the mitotic spindle gains access to the chromosomes. During this phase, a protein structure called the kinetochore is associated with the centromere on each sister chromatid. Stringlike structures called microtubules grow out from the spindle and connect to the sister chromatids at their kinetochores; one microtubule from one side of the spindle attaches to one sister chromatid in each chromosome, and one microtubule from the other side of the spindle attaches to the other sister chromatid Figure 3a.

Figure 3: a Metaphase and b Anaphase. In metaphase a , the microtubules of the spindle white have attached and the chromosomes have lined up on the metaphase plate. During anaphase b , the sister chromatids are pulled apart and move toward opposite poles of the cell.

Figure Detail. After metaphase is complete, the cell enters anaphase. During anaphase, the microtubules attached to the kinetochores contract, which pulls the sister chromatids apart and toward opposite poles of the cell Figure 3c. At this point, each chromatid is considered a separate chromosome.

Figure 4: During telophase, two nuclear membranes form around the chromosomes, and the cytoplasm divides. Finally, once anaphase is complete, the cell enters the last stage of the division process — telophase.

During telophase, the newly separated chromosomes reach the mitotic spindle and a nuclear membrane forms around each set of chromosomes, thus creating two separate nuclei inside the same cell. As Figure 4 illustrates, the cytoplasm then divides to produce two identical cells.

Why is mitosis important? As previously mentioned, most eukaryotic cells that are not involved in the production of gametes undergo mitosis. These cells, known as somatic cells , are important to the survival of eukaryotic organisms, and it is essential that somatic parent and daughter cells do not vary from one another.

With few exceptions, the mitotic process ensures that this is the case. Therefore, mitosis ensures that each successive cellular generation has the same genetic composition as the previous generation, as well as an identical chromosome set.

Watch this historic video from to see mitosis in action. Key Questions How do centromeres work? Key Concepts chromosomes replication meiosis. Topic rooms within Genetics Close. No topic rooms are there. Cells spend most of their life in this non-dividing phase.

See the graphic below. Prophase : The chromosomes coil and shorten, and become visible. It becomes apparent that the chromosomes have duplicated. Pairs of identical chromosomes remain attached to each other at the centromere and each chromosome is called a chromatid.

These chromatids are joined by a protein link called a kinetochore which holds the pair together until mitosis. Once the chromosomes have replicated, the cell contains double the normal number chromosomes until the cell divides. The full story of how the chromosomes replicate is complex, but a simplified way of thinking of this S phase replication is the unzipping of a strand of the two halves of DNA.

The unzipped DNA half strand is then matched up with a newly formed half strand. Because both halves receive a new half strand, the cell ends up with a double set of chromosomes.

The process of unzipping and forming a complementary half strand is completed by various enzymes and RNA molecules. With its double pack of chromosomes, the cell continues to grow and function through the G2 phase.

At the end of this phase, the cell forms structures called microtubules, which tug apart the chromatids by latching onto the kinetochore. Mitosis consists of four main events: prophase, metaphase, anaphase and telophase. During prophase, the nucleus of the mother cell breaks away, exposing the chromatids.