Mitosis and Meiosis

Mitosis and Meiosis

Mitosis is the cell division in which a cell will divide into two daughter cells that are identical to the original cell.

Meiosis is the cell division that results in the formation of gametes. Meiosis reduces the chromosome number from diploid to haploid. The products (haploids) formed from meiosis will have a complete set of chromosomes, and that each haploid is genetically different from each other.

Mitosis

• Prophase
• Sister chromatids condense and become more visible and thicker.
• Kinetochores develop in the centromere regions  
• The nucleolus disappears
• The nuclear envelope disappears

• Metaphase
• Chromosomes line up on the center of the cell (equatorial plate).
• They were moved to the center by the spindles coming from the opposite ends of the cell, where the centrioles are.

• Anaphase
• The centromeres of each of the chromosome are pulled by the spindle fibers.
• The sister chromatids are separated.
• They are now referred to as daughter chromosomes.
• Telophase
• New nuclei form around the chromosomes from each end of the cell
• The chromosomes uncoil and become less visible
• Spindle breaks apart
• After mitosis, cytokinesis takes place and the cell is split into two cells.

Meiosis

• Prophase I
• Chromosomes thicken and become more visible
• Homologous chromosomes pair
• Four sister chromatids form a tetrad
• Crossing over, or the exchange of genetic materials at the chiasmata, occurs
• This will increase variability
• Nucleoli disappear
• Nuclear envelope disappear
• Spindle forms

• Metaphase I
• Chromosome pairs are lined up at the center of the cell (equatorial plate).

• Anaphase I
• The homologous chromosomes separate
• The daughter nuclei will contain one set of chromosomes, and each chromosome has two chromatids
• Telophase I
• This doesn’t occur in all organisms
• If this stage occurs in an organism, then the nuclear envelope will form.
• Then cytokinesis occurs.

• Prophase II
• The chromosomes condense and become visible
• The nuclear envelope and nucleoli disappear

• Metaphase II
• The chromosomes, containing two chromatids, are lined up at the equatorial plate

• Anaphase II
• The sister chromatids separate

• Telophase II
• The haploid daughter cells start to form
• The nuclear envelope starts to form
• After Telophase II, cytokinesis takes place and produces 4 haploid daughter cells.

There are differences between meiosis II and mitosis:

• DNA will not replicate before meiosis II
• The sister chromatids in meiosis II will likely not be identical due to crossing over
• The number of chromosomes at the center of the cell in meiosis II is half the number of chromosomes in mitosis.

Meiosis results in 4 genetically different haploid nuclei

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