Meiosis

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Meiosis

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sexual reproduction- requires fertilized ( one sex cell from each parent joins together )
Division of a parent cell into four four daughters, cell called gametes.
haploid - half a set of chromosome with different genetic information.

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Meiosis 1

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Homologous chromosomes are separated into two daughter cells
Follows stages similar to Mitosis

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Prophase I

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Chromosomes form and each chromosome pairs with its homologous chromosome; called a tetrad – four chromatids
In a tetrad, homologous chromosomes can exchange portions of their chromatids; called crossing-over
Occurs at the chiasma
Creates recombinant chromatids (“recombined”)
Provides genetic variation – that’s how each one of us is very different from the other
Sexual reproduction creates genetic variation

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Metaphase I

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Tetrads line up in the middle, equatorial plane, of the cell

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Anaphase I

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Homologous chromosomes separate and move away from each other to opposite poles of the cell
Each is genetically different from the original cell due to crossing-over

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Telophase & Cytokinesis

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Nuclear envelope forms
Cytokinesis occurs resulting in two daughter cells
Daughter cells are NOT identical due to crossing-over in prophase I

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Meiosis I Overview

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Nondisjunction can occur when homologous chromosomes do not separate during anaphase I
There is an uneven distribution of chromosome to the two daughter cells, which may result in one daughter cell not having any chromosomes at all
At this stage, there is a higher risk of producing nonviable cells (not able to reproduce) during meiosis II
Genetic mutations in meiosis CAN be passed to offsprings