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 Happens in almost all cells (Somatic cells)  1 parent cell  Cell divides into 2 exact genetic copies with 46 chromosomes each  Stages are:  interphase  mitosis  Cytokinesis (2 cells formed)  Needed for:  growth and development  cell replacement  asexual reproduction of new organisms  regeneration

 Happens ONLY in sex cell formation (gametes)  2 parent cells called gametes with ½ the original chromosomes (23 in humans) are needed to create a new cell with mixed genetic code  How are they created?  Stages are  Interphase  4 stages of “mitosis” (meiosis I)  4 stages of “mitosis” AGAIN (meiosis II)  Cells split (4 gamete cells formed with ½ the of the original chromosomes)  Needed for genetic diversity and creating new organisms, both plant and animal

 How do the gametes only end up with half of the chromosomes?  This takes place during meiosis.  Meiosis is cell division that produces reproductive cells in sexually reproducing organisms (plants and animals).  Meiosis Video Meiosis Video

 Each chromosome duplicates like they did in interphase of mitosis.  Now the cell will go through 2 cycles of meiosis dividing the cell twice.  In mitosis, the chromosomes separated and moved away from each other.  In meiosis, the separation is different.

 First stage of meiosis:  Prophase I = copied chromosomes go close their duplicate.  Metaphase I = 2 pairs of chromosomes line up in the center of the cell as in mitosis.  Anaphase I = Each pair of chromosomes does NOT separate from each other but move away from the other pair.  Telophase I = cytoplasm divides creating 2 new cells, each with one original and one duplicated chromosome

 Prophase II = 2 cells have 2 duplicated chromosomes from Meiosis I  Metaphase II = Chromosomes line up in middle of each cell  Anaphase II = Chromatids separate and move to each end of each cell.  Telophase II = Nucleus reforms around each individual chromosome.  4 new cells have formed, each with ½ the number of chromosomes.

 2 cells form during meiosis I  Each of these cells form 2 cells in meiosis II  4 sex cells are created with ½ the chromosomes that were in the original nucleus  I humans 1 cell with 46 paired chromosomes results in 4 cells with 23 unpaired chromosomes

 Bats have 44 chromosomes in 22 pairs in their somatic cells. How many chromosomes are in each sex cell?  22 unpaired chromosomes  Dandelions have 24 chromosomes in 12 pairs in their somatic cells. How many chromosomes are in each sex cell?  12 unpaired chromosomes  King crab have 208 chromosomes in 104 pairs in their somatic cells. How many chromosomes are in each sex cell?  104 unpaired chromosomes