• Observe students and provide hints and feedback during the Phases of Meiosis activity.
• Assess their understanding of the information by randomly and frequently asking questions during the instructional portion to find out if students are grasping the information.
• Assess their understanding by asking them the review questions in the lesson.
• Observe students as they fill out Mitosis vs. Meiosis table. This will help assess whether or not they understand the differences between the two processes.
• Collect exit tickets for individual assessment.

Preparation: Use the instructions on the Phases of Meiosis resource (S-B-4-3_Phases of Meiosis.doc
). Place the index cards in a basket.

At the beginning of class, ask students if they have watched a TV program in which detectives or investigators obtain DNA samples to determine a person’s guilt or innocence in a crime. Then, inform students that a person’s unique DNA results from the combination of a mother’s DNA in her egg cell with a father’s DNA in his sperm cell. Relate that to this lesson by explaining that the egg and sperm result from the process of meiosis. Tell students, “The vocabulary words may look similar to mitosis, but they represent meiosis, a process with a similar-sounding name but a very different outcome.”

Write notes on the board that include the following major ideas:

“Sexual Reproduction

• Involves two parents, with the offspring receiving half its genetic information from one parent and half from the other.
• Results in greatly varied offspring.
• Meiosis is sexual reproduction on the cellular level.
• Meiosis forms gametes (sex cells). During meiosis, a diploid cell divides and the end result is four haploid cells.

Chromosomes

• Human somatic (body) cells have 23 pairs of chromosomes for a total of 46 chromosomes.
• The members of the 23 pairs are not identical; they are homologous chromosome pairs.
• The haploid number of human somatic cells (n) is 23 (23 unpaired chromosomes).
• The diploid number of human somatic cells (2n) is 46 (23 homologous chromosome pairs).
• The haploid and diploid numbers of different kinds of organisms are different (e.g., dogs have a haploid number of 34 chromosomes and a diploid number of 78 chromosomes).

Human Reproduction

• Human reproduction results from a haploid male gamete (sperm) fertilizing a haploid female gamete (egg) to form a diploid zygote.
• The 23 chromosomes from the male combine with the 23 chromosomes from the female to create offspring with 23 pairs of chromosomes in each somatic cell.”

Ask the class the following questions and have students write down their answers:

1.   “A horse has 32 pairs of homologous chromosomes. What is its haploid number?” (32) “What is its diploid number?” (64)

2.   “A new species being studied is found to have 19 pairs of chromosomes. Is this the haploid or diploid number?” (haploid number) “If this is the haploid, give the diploid number.” (38)

Have two to three students give their answers before revealing the correct answer. Briefly explain the correct answers for those who got them wrong. Say to the class, “Now that we have that information, let us look at the actual process of meiosis.” Tell students that meiosis occurs in two stages (meiosis I & II) with the phases of Meiosis II corresponding with the phases of mitosis. Ask students to recall the phases of mitosis, and have them say them out loud, writing them on the board in order: “Prophase, Metaphase, Anaphase, Telophase.”

Hand out the Meiosis Diagram sheets to students (S-B-4-3_Meiosis Diagram.doc). Have them read the descriptions and look at the pictures for the stages of meiosis for several minutes, then put the handout away. Have them check their understanding with the following activity.

Sequencing the Phases of Meiosis Activity

1.   Write the eight phases of meiosis across the board.

2.   Ask for eight volunteers to come to the front of the classroom and choose an index card from the basket.

3.   Have the volunteers read the description side of the card (keeping the other side with the phase name covered).

4.   Have the class arrange the volunteers in the order of the phases of meiosis and have the volunteers stand under their proper heading on the board.

5.   Once the class reaches a general consensus, have the volunteers read their cards one more time and give the class an opportunity to change the lineup.

6.   After the class settles on a sequence, rearrange the volunteers as needed to place them in the correct order under the proper headings. Have the volunteers read the phase names and proper sequence to the class.

Emphasize that Meiosis I results in 2 haploid cells that have duplicated chromosomes, so they need to undergo meiosis II.

Hand out the Additional Meiosis Information sheets (S-B-4-3_Additional Meiosis Info and KEY.doc). Go over the additional information, having students fill in the blanks as you read through and explain the sheet.

Tell the class, “Now we will examine the process of meiosis in human sex cells and reproduction.” Hand out the Gametogenesis sheet (S-B-4-3_Gametogenesis.doc). Have students take about 1–2 minutes to look over the differences between meiosis that results in sperm and in eggs.

Write the following notes on the board (or project them onto a screen with the overhead projector), and instruct students to copy them. Read each note aloud before you write it.

1.   “Male gametes grow a flagellum after telophase II.

2.   The flagellum allows the sperm to move in search of an egg.

3.   In females, one of the two cells produced at the end of telophase I takes most of the cytoplasm and organelles and is much bigger than the other.

4.   Both cells undergo meiosis II, but the smaller cell produces two very small gametes.

5.   When the big cell reaches telophase II, one of the gametes takes most of the cytoplasm and organelles and is much bigger than the other.

6.   Female meiosis II results in 3 small and 1 large gametes.

7.   The three small gametes are polar bodies.

8.   Only the large gamete, the egg, can produce a viable zygote if fertilized.

9.   Eggs are much larger than sperm.

10. Eggs are stationary but sperm are mobile.”

Say to the class, “We have studied mitosis and meiosis, now let us look at the differences between the two.”

Hand out the Mitosis vs. Meiosis sheet (S-B-4-3_Mitosis vs. Meiosis and KEY.doc) and have students take about 5 minutes to look over it and fill out the table. After giving them a chance to complete the table, go over the answers with them.

Ask the class the following questions and have students write down their answers:

• “A cellular reproduction process produces four diploid cells. Is this mitosis or meiosis?” (mitosis) “How many cells underwent this process?” (2 cells)
• “A cellular reproduction process produces four haploid cells. Is this mitosis or meiosis?” (meiosis) “How many cells underwent this process?” (1 cell)
• “A sperm cell swims to a polar body and attempts to fertilize it. Will a viable zygote develop?” (no)

Have two to three students give their answers before revealing the correct answers. Briefly review the correct answers and address any student questions.

Optional: Assign the Lesson 3 Meiosis Exit Ticket to students as a wrap-up to the lesson (S-B-4-3_Meiosis Exit Ticket and KEY.doc). This provides a quick assessment technique to identify any student deficiencies.

Extension:

• Students who may be going beyond the standards may research karyotyping. Define what a karyotype is, and write a paragraph on karyotyping and how it relates to chromosomes, haploid, and diploid cells.
• Students who might need an opportunity for additional learning can go to the Web site http://www.cellsalive.com/meiosis.htm and click on “Start the Animation.” Have students watch the animation and read descriptions of phases of meiosis to review the process.
• Students who might need an opportunity for additional learning can complete the Mitosis and Meiosis Review (S-B-4-3_Mitosis and Meiosis Review and KEY.docx).