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Meiosis

Meiosis is the form of eukaryotic cell division that produces haploid sex cells or gametes (which contain a single copy of each chromosome) from diploid cells (which contain two copies of each chromosome). The process takes the form of one DNA replication followed by two successive nuclear and cellular divisions (Meiosis I and Meiosis II). As in mitosis, meiosis is preceded by a process of DNA replication that converts each chromosome into two sister chromatids.

 

The stages of meiosis can be broken down into two main stages, Meiosis I and Meiosis II

- Meiosis I can be broken down into four substages: Prophase I, Metaphase I, Anaphase I and Telophase I

- Meiosis II can be broken down into four substages: Prophase II, Metaphase II, Anaphase II and Telophase II

Meiosis I

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Crossing Over

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  • Genetic material from the homologous chromosomes is randomly swapped

  • This creates four unique chromatids

  • Since each chromatid is unique, the overall genetic diversity of the gametes is greatly increased

 

Metaphase I

  • Microtubules grow from the centrioles and attach to the centromeres

  • The tetrads line up along the cell equator

Compare Metaphase I to Metaphase II and to the Metaphase stage of mitosis.

 

 

 

 

 

Anaphase I

  • The centromeres break and homologous chromosomes separate (note that the sister chromatids are still attached)

  • Cytokinesis begins

Compare Anaphase I to Anaphase II and to the Anaphase stage of mitosis.

 

 

 

Telophase I

  • The chromosomes may decondense (depends on species)

  • Cytokinesis reaches completion, creating two haploid daughter cells

Compare Telophase I to Telophase II and to the Telophase stage of mitosis.

 

 

 

 

 

 

 

 

Prophase I - most of the significant processes of Meiosis occur during Prophase I

  • The chromosomes condense and become visible

  • The centrioles form and move toward the poles

  • The nuclear membrane begins to dissolve

  • The homologs pair up, forming a tetrad

    • Each tetrad is comprised of four chromotids - the two homologs, each with their sister chromatid

  • Homologous chromosomes will swap genetic material in a process known as crossing over (abbreviated as XO)

    • Crossing over serves to increase genetic diversity by creating four unique chromatids

Compare Prophase I to Prophase II and to the Prophase stage of mitosis.

Meiosis II

 

 

Prophase II

  • Centrioles form and move toward the poles

  • The nuclear membrane dissolves

Compare Prophase II to Prophase I and to the Prophase stage of mitosis.

 

 

 

 

 

 

 

 

 

 

Metaphase II

  • Microtubules grow from the centrioles and attach to the centromeres

  • The sister chromatids line up along the cell equator

Compare Metaphase II to Metaphase I and to the Metaphase stage of mitosis.

 

 

 

 

 

 

 

 

 

 

Anaphase II

  • The centromeres break and sister chromatids separate 

  • Cytokinesis begins

Compare Anaphase II to Anaphase I and to the Anaphase stage of mitosis.

 

 

 

 

 

 

 

 

 

 

Telophase II

  • The chromosomes may decondense (depends on species)

  • Cytokinesis reaches completion, creating four haploid daughter cells

Compare Telophase II to Telophase I and to the Telophase stage of mitosis.
 

Leena Huynh  Biology Set 1 

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