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Meiosis

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Meiosis is the division of precursor reproductive cells to produce haploid gametes (cells that combine with a sperm or egg to form a zygote). The processes that occur during Meiosis ensure that offspring are not genetically identical to their parents, maintaining genetic variation within a population.


PROPHASE I

Homologous chromosomes (chromosomes that are of the same size and have identical gene locations) pair up in the process of Synapsis, forming a tetrad. Crossing over occurs between the chromosomes, in which each chromsome exchanges a chromatid with their partner. (Note: Each person inherits a set of chromosomes from their parents, so half of their chromosomes came from their mother and half of their chromosomes came from their father. In a homologous tetrad, one of these chromosomes came from mom while the other one came from dad.)

METAPHASE I

The homologous tetrads line up next to eachother over the equator of the cell. The order in which they line up along the equator varies:

For example: Both Hemispheres separated by the equator may contain an integrated row of chromosomes inherited from both the mother and father. In another case, it is possible that both hemispheres can be completely segregated: one hemisphere contains a row of chromosomes only inherited from the mother, while the other one may contain chromosomes only inherited from the father.

The idea that chromosomes align randomely over the equator of a cell is called the law of independent assortment.

Spindle fibers attach to the center of each chromosome.

ANAPHASE I

Homologous Chromosomes separate, as the spindle fibers (attached by centrosomes) pull toward opposite poles of the cell.

TELOPHASE I /CYTOKINESIS

The cell elongates and then divides into two haploid cells.

PROPHASE II


METAPHASE II


ANAPHASE II


TELOPHASE II /CYTOKINESIS

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