Ed Golson Outdoor Education

What is meiosis?

While mitosis is used for asexual reproduction resulting in the daughter cells looking just like the parent cells, Meiosis is used for sexual reproduction in order to create offspring with different genetic material.  Since human cells contain 46 chromosomes, the combination of two separate cells would double the amount.  Meiosis gets rid of the extra chromosomes because sex cells are produced called gametes that have only 23 chromosomes.  These cells are called haploid cells because they only have half of the original number of chromosomes.  The cell with the original number of chromosomes is called diploid.  23 chromosomes come from the mother and 23 come from the father. During reproduction they fuse together to create an offspring with different genetic material than either parent.  The process of creating haploid cells occurs in two stages; meiosis I and meiosis II.

Meiosis I

 

Meiosis II

Prophase 1:  During this stage each chromosome duplicates and remain associated.  They are now called sister chromatids.  Also during this stage crossing-over can occur.   Prophase 2:  During this stage each cell contains sister chromatids, and spindle fibers are produced from the poles of the cell.  The cell is simply preparing for the next step.
Metaphase 1:  During this stage the chromosomes align in the across the center line of the cell, sometimes known as the equatorial plate.   Metaphase 2:  Once again during this stage the chromosomes align across the equatorial plate.
Anaphase 1:  During this stage the pairs separate while the sister chromatids stay together.   Anaphase 2:  During this stage centromeres divide and the sister chromatids separate and move to each end of the cell.
Telophase:  During this stage two daughter cells are formed but each daughter contains only one chromosome of the pair.   Telophase 2:  During this stage cell division is complete and you are left with four haploid daughter cells.

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