Meiosis
Definition: Two stage cell divisions in sexually reproducing organisms, where total of four haploid cells are produced.
Prophase I:
– DNA in non-sister chromosomes crosses over. ( exchanges segments)
– Each chromosome pair forms a tetrad, group of four chromatids.
– Nucleolus membrane breaks down into fragments.
Metaphase I:
– Pairs of homologous chromosomes, tetrads, are lined on the metaphase plate.
– Chromosomes of each pair lines up facing each pole.
Anaphase I:
– The chromosomes, two sister chromatids, move toward the opposite side of the cell
– Sister chromatids remain together (attached) and moves toward the same side.
Telophase I & Cytokinesis:
– Each half of the cell has complete haploid set of chromosomes.
– Cytokinesis occurs simultaneously with telophase I.
– In animal cells, cleavage furrow occurs and divides the parent cells into two haploid daughter cells.
– In plants, cell plate separates and divides the cell.
Prophase II:
– Spindle fibers appear.
– Chromosomes are moving toward the middle of the cell
Metaphase II:
– Chromosomes are lined on the metaphase plate.
– Because of the cross over in prophase I, sister chromatids are not genetically identical.
– Kinetochores are attached to microtubules.
Anaphase II:
– Centromeres of each chromosome separate, and the sister chromatids are divided.
– Each sister chromatids move toward the opposite end of the cell.
Telophase II & Cytokinesis:
– Nuclei forms and chromosomes begin to de-condense.
– One meiotic parent cell produces four haploid daughter cells.
– Each of the four daughter cells is not genetically identical.
Here are some animations to help you!
This site has narration, step by step teachings, and quizzes.
http://www.sumanasinc.com/webcontent/animations/content/meiosis.html
SEE IF YOU KNOW EVERYTHING:)
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