Cellular Division: Mitosis and Meiosis
Mitosis and Meiosis
Hi, and welcome to this video on cell replication, otherwise known as mitosis or meiosis. First, let’s start with mitosis. The primary events that occur during mitosis are interphase (the cell prepares for division by replicating its genetic and cytoplasmic material). Interphase can be further divided into G1, S, and G2.
Then there’s prophase (the chromatin thickens into chromosomes and the nuclear membrane begins to disintegrate). Pairs of centrioles move to opposite sides of the cell and spindle fibers begin to form. The mitotic spindle formed from cytoskeleton parts moves chromosomes around within the cell.
Metaphase (the spindle moves to the center of the cell and chromosome pairs align along the center of the spindle structure). Then, there’s anaphase (the pairs of the chromosomes called sisters begin to pull apart and may bend). When they are separated, they’re called daughter chromosomes.
Grooves begin to appear in the cell membrane. Then, there’s telophase (the spindle disintegrates, the nuclear membranes reform, and the chromosomes revert to chromatin. In animal cells, the membrane is pinched. In plant cells, a new cell wall begins to form. Then, there’s cytokinesis.
This is the physical splitting of the cell, including the cytoplasm, into two cells. Some believe this occurs following telophase. Others say it occurs from anaphase as the cell begins to furrow through telophase when the cell actually splits into two. Let’s talk about meiosis. Meiosis has the same phases as mitosis, but they happen twice.
In addition, different events occur during some phases of meiosis than mitosis. The events that occur during the first phase of meiosis are interphase (I), prophase (I), metaphase (I), anaphase (I), telophase (I), and cytokinesis (I). During this first phase of meiosis, chromosomes cross over, genetic material is exchanged, and tetrads of four chromatids are formed.
The nuclear membrane dissolves, homologous pairs of chromatids are separated and traveled to different poles. At this point, there has been one cell division resulting in two cells. Each cell goes through a second cell division, which consists of prophase (II), metaphase (II), anaphase (II), telophase (II), and cytokinesis (II).
The result is four daughter cells, each with different single sets of chromosomes. The daughter cells are haploid, which means they contain half the genetic material of the parent cell. The second phase of meiosis is similar to the process of mitosis, but meiosis encourages more genetic diversity.
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