Lab 10-Cell Division - Lecture notes 1 PDF

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Lab 10: Cell Division Objectives:   

Understand the steps of Mitosis and be able to visualize and identify the various stages. Understand the steps of Meiosis and be able to visualize and identify the various stages. Describe the differences between mitosis and meiosis.

Introduction The life of a typical body cell (somatic cell) involves periods where the cell is carrying out all of the normal metabolic reactions of the cell and times when the cell is dividing in order to facilitate the growth, repair, and maintenance of living organisms. During this cell cycle, cells spend around 90% of their time in what we call Interphase. This portion of the cells cycle involves three phases: 1. G1 Phase – the first gap phase in which a cell is carrying out the normal functions of the cell 2. S Phase – the synthesis phase occurs when a cell is getting ready to divide and includes the synthesis or replication of DNA to ensure that both daughter cells receive identical copies of the DNA. 3. G2 Phase – the second gap phase occurs after synthesis and is a time when the cell is preparing all of the other components in the cell for actual cell division. The other portion of the cells cycle involves the M phase. During this portion, the cell is actually going to divide through two separate processes. The first process is the division of the genetic material (Mitosis) and the second is the division of the cytoplasm (Cytokinesis). Cytokinesis often follows so rapidly after the last stage of mitosis, that it is often addressed together. In addition, cytokinesis is different in plant and animal cells. During Mitosis and Cytokinesis, the sister chromatids produced during the S Phase separate through a series of four steps: 1. Prophase – During prophase, the nuclear envelope begins to break apart, the nucleolus disappears, and the sister chromatids begin to condense and become visible. 2. Metaphase – During metaphase, the sister chromatids line up along the center of the cell, known as the metaphase plate. In addition, a mitotic spindle forms and attaches to the sister chromatids. 3. Anaphase – Anaphase is characterized by the sister chromatids moving to opposite poles of the cell due to the mitotic spindle pulling them apart and forming daughter chromosomes. 4. Telophase/Cytokinesis – During telophase the daughter chromosomes begin to relax and the nucleolus and the nuclear envelope begin to reform. Cytokinesis occurs when the actual cell begins to divide. Another form of cell division involves the production of reproductive cells known as gametes (eggs and sperm). This process is known as Meiosis. Meiosis is achieved through two distinct nuclear divisions which reduces the number of chromosomes in the egg and sperm by half. The first nuclear division is known as Meiosis I and consists of: 1. Prophase I - in which the homologous pairs of chromosomes align together through a process known as synapsis to create a tetrad. This is also when the process of crossing over occurs as portions of the homologous chromosomes are exchanged. 2. Metaphase I – the homologous chromosomes line up along the metaphase plate. During metaphase I, homologous pairs line up independently of each other (Law of Independent Assortment) which allows for a great deal of genetic variation. 3. Anaphase I - during this phase, the homologous chromosomes separate from each other ( Law of Segregation) and each daughter cell receives one of the homologous chromosomes. 4. Telophase I – the final stage of Meiosis I, in which the sister chromatids move to opposite poles and two cells are produced.

The second nuclear division is known as Meiosis II and consists of Prophase II, Metaphase II, Anaphase II, and Telophase II. The process of Meiosis II is very similar to that of Mitosis and the outcome is the division of the sister chromatids. This results in four unique daughter cells that contain half the number of chromosomes found in the parent cell.

Activity One: Mitosis in Plant and Animal Cells For this activity, you will be using a microscope and select slides to view the various stages of the cell cycle for both plants and animals. Materials Animal Mitosis slide (Whitefish Blastula) Plant Mitosis slide (Allium root) Procedure 1. Obtain the two mitosis slides and identify the five stages of the cell cycle. In the table below, draw the chromosomes or sister chromatids inside the cell (the circle) and list the characteristics of the phase. Drawing

TELOPHASE

ANAPHASE

METAPHASE

PROPHASE

INTERPHASE

Animal

Characteristics Plant

Activity 2: Mitosis Scramble: Using the Mitosis Model, place the various stages in order from start to finish and describe the events occurring. NOTE: Not all of the stages will be present and some stages might have more than one “cell” associated with them. Procedure: 1. Complete the following table for Mitosis.

EVENT # 1.

2.

3.

4.

5.

6.

7.

8.

9.

LETTER

DESCRIPTION OF EVENTS OCCURRING

Activity 3: Meiosis Observe the demonstration slides for the various stages of Meiosis in plants and animals. Procedure 1. Draw the various stages of Meiosis below and indicate what type of specimen it is and what stage of meiosis is shown.

Specimen: ______________________

Specimen: ______________________

Stage of Meiosis: __________________

Stage of Meiosis: __________________

Specimen: ______________________

Specimen: ______________________

Stage of Meiosis: __________________

Stage of Meiosis: __________________

Specimen: ______________________

Specimen: ______________________

Stage of Meiosis: __________________

Stage of Meiosis: __________________

Activity 4: Meiosis Scramble: Using the Meiosis Model, place the various stages in order from start to finish and describe the events occurring. NOTE: Not all of the stages will be present and some stages might have more than one “cell” associated with them. Procedure: 1. Complete the following table for Meiosis. EVENT # 1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

LETTER

DESCRIPTION OF EVENTS OCCURRING...