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Lab 2: Mitosis & Meiosis
Please bring your textbook to lab!
Today you will work in groups of five to act out mitosis and meiosis in front of the class. You will have a few props available (string, paper, markers); mostly you must use your creativity. You will have 20 minutes to prepare each performance. Each performance should be no more than three minutes long. Make sure that everyone plays a part in the performance and that it is an active and entertaining—and accurate—performance. The grading rubric is on the last page. Mitosis and meiosis are summarized below to help you in your performance planning.
Introduction
The basic unit of life, the cell, must duplicate itself. One “mother” cell becomes two “daughter” cells through the process of cell division—usually this involves mitosis, but some cells undergo meiosis.
Mitosis is a completely asexual event and involves
replication of the chromosomes in the nucleus followed by dividing up of the cytoplasm to make two identical daughter cells. Remember, mitosis allows organisms to
grow by increasing the number of cells.
Meiosis, on the other hand, is involved only in sexual
reproduction, and is the main source of genetic
variation. In meiosis, chromosomes within the nucleus replicate but then the cells divide twice. This yields cells with half as many chromosomes. These cells become the egg and the sperm that unite later in a process known as
fertilization. Remember, meiosis occurs only during sexual reproduction and is what creates eggs and sperm, which are all genetically different from one another.
Part I: The Cell Cycle and Mitosis
In actively dividing cells, the term cell cycle is used to describe the life history of the cell. The cell cycle involves three phases:
1. Mitosis: the replication of chromosomes and formation of two daughter nuclei 2. Cytokinesis: the division of the cytoplasm and building of a new cell wall between
the daughter cells.
3. Interphase: a period during which the cell grows large enough to divide again.
Cell division KEY WORDS
Mitosis: the asexual process by which one cell divides into two identical cells. Meiosis: the process by which one diploid cell divides into four genetically different haploid sex cells (a.k.a. gametes; eggs or sperm). Diploid: a cell that contains two homologous copies of each
chromosome, one from the mother and one from the father.
Haploid: a cell that contains one copy of each chromosome. Sex cells, or gametes, are usually haploid.
Cytology: the study of cells. Cytokinesis: the division of the
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In plants, mitosis occurs predominantly in meristems: the root and stem tips, vascular and cork cambium, and in organs in their early stages of growth.
Interphase is divided into three segments:
1. G1: growth or gap 1. Proteins required for DNA
replication are made and organelle content doubles.
2. S: synthesis. DNA is replicated so that
chromosomes double (chromosomes are made of DNA). This is necessary because during mitosis the chromosomes of one nucleus are divided between the two new nuclei.
3. G2: growth or gap 2. Proteins required for cell
division are synthesized.
Mitosis is divided into four stages:
1. Prophase: chromatin condenses and chromosomes can be seen under the microscope.
Chromosomes migrate to opposite sides of the cell and spindle fibers begin to appear.
2. Metaphase: chromosomes line up along the metaphase plate. The centromeres of each
sister chromatid are attached to spindle fibers.
3. Anaphase: chromatids of each chromosome separate at the centromeres and move to
opposite sides of the cell. Each chromatid is now called a chromosome.
4. Telophase: the spindle apparatus disappears, and the nuclear membrane reappears and
forms two separate nuclei, one for each daughter cell. The chromosomes uncoil and become chromatin.
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Meiosis is divided into two parts and eight stages: Meiosis I
1. Prophase I: fully condensed chromosomes can be seen under the microscope. Spindle
fibers begin to appear. Crossing-over occurs between homologous chromosome pairs.
2. Metaphase I: homologous chromosomes line up along the metaphase plate. The
centromeres of each chromosome are attached to spindle fibers.
3. Anaphase I: homologous chromosomes (containing both sister chromatids) are pulled
apart by the spindle fibers and move to opposite sides of the cell.
4. Telophase I: the spindle apparatus disappears, and the nuclear membrane reappears
and forms two separate nuclei.
Meiosis II
5. Prophase II: spindle fibers begin to appear.
6. Metaphase II: chromosomes line up along the metaphase plate. The centromeres of
each sister chromatid are attached to spindle fibers.
7. Anaphase II: chromatids of each chromosome separate at the centromeres and move to
opposite sides of the cell. Each chromatid is now called a chromosome.
8. Telophase II: the spindle apparatus disappears, and the nuclear membrane reappears
and forms two separate nuclei, one for each daughter cell. The chromosomes uncoil and become chromatin.
Meiosis II is almost the same process as mitosis; Meiosis I is when genetic differences originate (during crossing-over and lining up along the metaphase plate).
IMPORTANT TERMS TO DIFFERENTIATE
Chromosome: a coiled mass of DNA that a carries genes. One chromosome contains only a portion of the DNA in a nucleus.
Sister chromatids: two pieces of DNA, attached at the centromere, containing identical DNA. Sister chromatids are the result of DNA replication. Sister chromatids separate in mitosis and during meiosis II.
Homologous chromosomes: members of pairs of chromosomes (one derived from each parent) that are similar in size and gene location. Homologous chromosomes pair and crossing over occurs during prophase I. Homologous chromosomes separate during meiosis I.
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5 Grading Rubric for Performances
CATEGORY 2 1 0 TOTAL
Content Shows a full
understanding of mitosis/meiosis. Shows a good understanding of parts of the topic.
Does not seem to understand the topic very well. Collaboration
with Peers Always listens to, shares with, and supports the efforts of others in the group. Tries to keep people working well together. Everyone participates in the presentation actively and to a roughly equal degree.
Often listens to, shares with, and supports the efforts of others in the group but sometimes is not an effective team member.
Rarely listens to, shares with, and supports the efforts of others in the group. Participation is not at all balanced among group members. Enthusiasm Facial expressions and
body language generate a strong interest and
enthusiasm about the topic in others. Facial expressions and body language generate moderate enthusiasm in others.
Very little use of facial expressions or body language. Did not generate much interest in topic being presented. Time-Limit Presentation is 2-3
minutes long. Presentation is more than 3 minutes long or less than 1 minute long.
Preparedness Given the short time to prepare, student is completely prepared, knows the material, and has obviously rehearsed.
Given the short time to prepare, the student is somewhat prepared, but it is clear that rehearsal and/or knowledge of the topic was lacking.
