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Meiosis
Unit –
Cell Reproduction
Biology
Meiosis
• Process of cell division
that reduces the number
of chromosomes to half
• Produces haploid cells
called gametes
• Gametes are….
• Each gamete contains
23 chromosomes
Egg
cell
Sperm cells
Meiosis
One replication, two divisions
Interphase I (G1, S, G2)
• chromosomes replicate to
produce homologous pairs (sister
chromatids)
Meiosis I
• homologues separate
Meiosis II
• sister chromatids separate
Meiosis I
Interphase
• cell grows to mature size
• copies its DNA
Meiosis I
Prophase I
• DNA coils tightly into chromosomes
• Spindle fibers appear
• Nucleus disappears
Meiosis I
Metaphase I
• Tetrads line up in the middle
• They line up randomly with respect to the poles
of the cell.
Meiosis I
Anaphase I
• Each homologous chromosome (consisting of
two chromatids) moves to opposite sides of the
cell
Meiosis I
Telophase I and Cytokinesis I
• Chromosomes reach opposite sides of cell
• Cytoplasm divides resulting in 2 cells
Prophase II
• DNA coils tightly into chromosomes
• Spindle fibers appear
• Nucleus disappears
Meiosis II
Metaphase II
• Chromosomes move to middle of each
cell
Meiosis II
Anaphase II
• Chromatids separate and move to
opposite poles of each cell
Meiosis II
Telophase II and Cytokinesis II
• A nuclear membrane forms around the
chromosomes in each of the 4 cells
• DNA unwinds to chromatin form
Meiosis II
Results in four new cells,
Each cell contains half of the original
cell’s number of chromosomes
Meiosis II
A Comparison
Mitosis
And
Meiosis