Meiosis and Sexual Reproduction

MeiosisReduction/Division

Reduction:• Process takes a ______

cell with two sets of chromosomes and reduces it to a _________ cell with one set of chromosomes

Begins after Interphase, when ______ replicates.

DNA

Division• The cytoplasmic

division of one cell into _____ cells.

diploid

haploidfour

Meiosis:Reduction/Division

Two divisions:

Meiosis I &

Meiosis II

Prophase I

Like Mitosis:

1. Nuclear membrane disappears

2. Spindles form

3. Chromatin condenses into chromatids

Unlike Mitosis:

1. Homologous chromosomes group with other homologous chromosomes to form a “tetrad”

2. A “chiasma” occurs at the point where the chromosomes cross over, detach, and exchange segments of the chromosome

Metaphase I

1. Homologous chromosomes line up at the metaphase plate.

2. Microtubules (spindles) attach to the kinetochore of centromere

Anaphase I

1. Homologous chromosomes separate.

2. Sister chromatids remain attached.

Telophase I

• Two daughter cells are formed with each one containing only one chromosome of the homologous pair.

• The daughter cells are now haploid.

Prophase II:• DNA does not

replicate. • Prophase II is just

like mitotic prophase.

Meiosis II:Gamete formation

Metaphase II:

• All of the chromosomes line up at the metaphase plate.

Anaphase II:

• Centromeres divide• Sister chromatids

migrate separately to each pole.

Telophase II / Cytokinesis:

• Chromosomes revert to chromatin.

• Nuclei reform.• Cytoplasm cleaves• Four haploid

daughter cells are obtained

Summary of Meiosis (video)

What is the difference between mitosis and meiosis? (flash)

Based on the image alone, fill in the Venn Diagram comparing and contrasting mitosis from meiosis. Then watch the flash video with your class, and add

information to your graphic organizer.