CELLS alive!


Meiosis is important in assuring genetic diversity in sexual reproduction. Use this interactive animation to follow Meiosis I (reduction division) and Meiosis II in a continuous sequence or stop at any stage and review critical events.

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Events during Meiosis

Diploid Cell (2N): From a preceding mitotic division, the Oogonium (Spermatogonium) enters meiosis with DIPLOID (2N) chromosomes but TETRAPLOID (4N) DNA. Chromosomes then duplicate to produce SISTER CHROMATIDS (or HOMOLOGOUS DYADS).

Prophase I: Dyad pairs align to create "TETRADS", non-sister chromatids connect and trade sections at a "CHIASMA", a process called "CROSSING OVER".

Metaphase I: SPINDLE FIBERS attach to each dyad at the KINETOCHORE. Tension from spindle fibers aligns the tetrads at the cell equator.

Anaphase I: Chiasmata break apart and sister chromatids begin migrating toward opposite poles.

Telophase I: CLEAVAGE FURROW forms beginning the process of CYTOKINESIS (cell division). Resulting daughter cells are HAPLOID (1N).

Prophase II: Spindle formation begins and centrosomes begin moving toward poles.

Metaphase II: Tension from spindle fibers aligns chromosomes at the metaphase plate.

Anaphase II: CHROMATIDS separate and begin moving to the poles.

Telophase II: CLEAVAGE FURROW forms beginning CYTOKINESIS.

Gamete (1N): NUCLEAR ENVELOPES form and chromosomes disperse as CHROMATIN. Meiosis has produced 4 DAUGHTER CELLS, each with 1N chromosomes and 1N DNA. Later, in fertilization, male and female 1N gametes will fuse to form a 2N ZYGOTE.