Meiosis

Meiosis Two rounds of cell division (Meiosis I and Meiosis II) Results in 4 haploid cells We need this to create gametes (sex cells)

Key Terms Homologous chromosomes Sister chromatids Two separate chromosomes that have the same genes One from your mother and one from your father Sister chromatids Each half of one chromosome Homologous chromosomes are divided in meiosis I and sister chromatids will be divided in meiosis II.

Meiosis Similar process to mitosis Meiosis I Meiosis II Prophase I Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II

Prophase I Nuclear membrane breaks down, centrioles move to opposite sides of the cell. Homologous chromosomes pair up.

Prophase I Crossing over When homologous chromosomes pair, parts of them may break off and reattach to the other. This increases genetic variation!

Metaphase I Homologous chromosomes line up along the middle of the cell. Each side has chromosomes from both parents.

Anaphase I Homologous chromosomes separate and move to opposite ends of the cell.

Telophase I Two nuclei are formed Cytokinesis

Meiosis II During Meiosis I, we divided homologous chromosomes. In Meiosis II, we will divide sister chromatids.

Prophase II Nuclear membrane breaks down Centrioles move to opposite sides of the cell Same as prophase I or prophase in mitosis!

Metaphase II Chromosomes line up along the middle of the cell.

Anaphase II Sister chromatids pulled apart to opposite sides of the cell.

Telophase II Nuclear membrane reforms Cytokinesis Results in four haploid cells with a combination of genes from both mother and father

Gamete Formation Spermatogenesis= production of four haploid sperm cells from one diploid spermatagonium

Gamete Formation Oogenesis= one diploid oocyte divides unevenly, forming one haploid egg and three unusable polar bodies.

Mitosis vs. Meiosis Cell division

Mitosis/Meiosis Review What kind of cells are produced by mitosis? What kind of cells are produced by meiosis? What is the difference between meiosis I and meiosis II? What is crossing over and when does it occur? Which process contributes more to genetic diversity (mitosis or meiosis)? Why?

Meiosis Simulation Arrange your “chromosomes” to simulate each stage of meiosis. Draw the chromosome arrangement in the template provided. Next to each picture, provide a brief description of what occurs during that stage. When you are finished, answer the following questions: What is the difference between meiosis I and II? Which round of meiosis is more similar to mitosis? Why?