Meiosis

Meiosis

Essential Content

A. Process: Creating Gametes and Independent Assortment (16.16)

1. Role of Meiosis in Organisms

a. Production of Non-Identical Haploid Daughter Cells

b. Function of Haploid Cells in Sexual Reproduction

2. Haploid vs. Diploid Cells

3. Stages: Meiosis I and Meiosis II

4. Introduction to Independent Assortment of Chromosomes

5. Organelle responsible

B. Crossing Over and Non-Disjunction (16.16)

1. Crossing Over (Genetic Recombination)

2. Non-Disjunction

C. Genetic Variation Resulting From Meiosis (16.16)

1. Role of Meiosis in Sexual Reproduction/ production of spores

2. Function of Sexual Reproduction in genetic variation

D. Comparison of Mitosis and Meiosis (16.17)

1. Location

2. Function (Replication and separation of genetic material)

3. Changes in Chromosome number

4. Number of Cell Divisions and Products

Objectives

· Connect specific events to specific stages of the cell cycle. (ALD)

· Describe the process of meiosis I and meiosis II and what is occurring specifically at each phase.

· Explain crossing over and how it affects the phenotype in a species and contributes to genetic variation.

· Describe the role of meiosis in sexual reproduction and how it contributes to genetic variation.

· Describe the role meiosis plays in the formation of haploid gametes or spores.

· Compare and contrast homologous chromosomes and sister chromatids.

· Differentiate between haploid and diploid cells.

· Explain how independent assortment during meiosis contributes to genetic variation.

· Explain how mutations in gametes may result in phenotypic changes in offspring.

· Describe the process of independent assortment (will be Segway to Topic XIX) in the resulting cells in meiosis.

Differentiate the processes of mitosis and meiosis and/or show how these processes may contribute to or limit genetic variation

What is Meiosis?

The process that produces haploid gametes is meiosis (egg and sperm). Meiosis is a type of cell division in which the number of chromosomes is reduced by half. It occurs only in certain special cells of the organisms. During meiosis, homologous chromosomes separate, and the haploid cells that form have only one chromosome from each pair. Two cell divisions occur during meiosis, and a total of four haploid cells are produced. The two cell divisions are called meiosis I and meiosis II.

Phases of Meiosis

Meiosis I begins after DNA replicates during interphase. In both meiosis I and meiosis II, cells go through the same four phases as mitosis. However, there are important differences between meiosis I and mitosis.

Meiosis I

1. Prophase I: The nuclear envelope begins to break down, and the chromosomes condense. Centrioles start moving to opposite poles of the cell, and a spindle begins to form. Importantly, homologous chromosomes pair up, which is unique to prophase I. In prophase of mitosis and meiosis II, homologous chromosomes do not form pairs in this way.

2. Metaphase I: Spindle fibers attach to the paired homologous chromosomes. The paired chromosomes line up along the equator of the cell. This occurs only in metaphase I. In metaphase of mitosis and meiosis II, it is sister chromatids that line up along the equator of the cell.

3. Anaphase I: Spindle fibers shorten, and the chromosomes of each homologous pair start to separate from each other. One chromosome of each pair moves toward one pole of the cell, and the other chromosome moves toward the opposite pole.

4. Telophase I and Cytokinesis: The spindle breaks down, and new nuclear membranes form. The cytoplasm of the cell divides, and two haploid daughter cells result. The daughter cells each have a random assortment of chromosomes, with one from each homologous pair. Both daughter cells go on to meiosis II.

Meiosis II

1. Prophase II: The nuclear envelope breaks down and the spindle begins to form in each haploid daughter cell from meiosis I. The centrioles also start to separate.

2. Metaphase II: Spindle fibers line up the sister chromatids of each chromosome along the equator of the cell.

3. Anaphase II: Sister chromatids separate and move to opposite poles.

4. Telophase II and Cytokinesis: The spindle breaks down, and new nuclear membranes form. The cytoplasm of each cell divides, and four haploid cells result. Each cell has a unique combination of chromosomes.

Crossing-Over of Tetrads......leads to greater genetic diversity.

Study Guide for Types of Cell Division

***Disclaimer: Study guide does NOT include the specifics on the phases of Meiosis.

PLEASE review notes and additional web resources listed above for the Meiosis section.****