Meiosis and Sexual Reproduction Activity 13 Meiosis and Sexual Reproduction

REVIEW… 1. How many cells result when one cell divides by mitosis? 2. How many chromosomes will be in the daughter cells compared to the number of chromosomes that were in the parent cell? 3. How many chromosomes are in human body cells? 4. What kinds of cells are made by mitosis? 5. What kinds of cells are NOT made by mitosis?

Assume that gametes (egg & sperm) are made by mitosis… 46 How many chromosomes would be in a human egg? How many chromosomes would be in a human sperm? How many chromosomes would be in a human zygote when the egg & sperm unite during fertilization? 46

Chromosome number would DOUBLE in every generation IF gametes were made by MITOSIS like all other body cells of an organism 92

Read the 2nd paragraph of the introduction. What is MEIOSIS? Where does meiosis occur? What is the significance of meiosis? Briefly review the history of scientific knowledge about the passing of hereditary information from parents to offspring. Also closely review the photographs in the student book with the class. For more information on having this class discussion see the Teacher’s Edition for this activity.

MEIOSIS… Like mitosis…is a form of cell division Reduces the chromosome number to HALF the number of chromosomes in the body cells of an organism occurs in developing sex cells. Ensures that the chromosome number does not DOUBLE in the next generation of the species

How do chromosomes divide during the formation of egg and sperm cells? Challenge How do chromosomes divide during the formation of egg and sperm cells?

MEIOSIS SIMULATION: SEPUP Link to the simulation on my pbworks page You will draw & describe each phase of meiosis You will model the process by using popbeads

Stages of meiosis Prophase I Prophase II Metaphase I Metaphase II Anaphase I Anaphase II Telophase I Telophase II Sample answers to Student Sheet 13.1, “Meiosis,” and 13.2, “Mitosis and Meiosis Comparison” can be found on the Science and Global Issues website (sepuplhs.org/sgi).

Homologous Chromosomes A key difference between Mitosis & Meiosis…is that the chromosomes form HOMOLOGOUS PAIRS Chromosomes that have the genes for the same traits. These genes must be in the same order on the chromosome. They do not have to be identical alleles. EXAMPLE: Can be S and S, S and s, or s and s. ARRANGE THE CHROMOSOMES AT YOUR DESK INTO HOMOLOGOUS PAIRS

Homologous Chromosomes Before Replication After Replication Before Replication After Replication

Cell Types A cell with two of each kind of chromosome is called a DIPLOID cell. All Body cells Chromosomes form homologous pairs A cell with only one of each type of chromosome is called a HAPLOID cell. Sex cells or gametes. No homologous pairs ½ the chromosomes found in body cells

Interphase The period between cell division Cell is growing & metabolizing Cell replicates its DNA NO CHROMOSOMES VISIBLE

Prophase I DNA coils into chromosomes which are now visible Centrioles separate & Spindles form Nucleus disappears Homologous chromosomes line up next to each other

CROSSING OVER Homologous chromosomes can exchange pieces of genetic material Occurs during PROPHASE 1 Increases genetic variety

Metaphase I Spindle is complete Centromeres become attached to a spindle fiber. The homologous chromosomes (tetrad) line up in the middle of the cell.

Anaphase I Homologous chromosomes separate One chromosome from each pair moves to opposite ends of the cell

Telophase I Chromosomes have reached opposite sides of cell Spindles break down Nucleus reforms Cytoplasm divides to form two new cells. RESULT: 2 cells ½ # chromosomes

Prophase II New spindles form Chromosomes are still made up of sister chromatids (replicated copy of DNA)

Metaphase II Chromosomes line up at the equator This time, they are single file as in mitosis

ANAPHASE II Sister chromatids separate and move to opposite ends of each cell.

Telophase II Cytoplasm divides Meiosis produces four haploid cells. Are they identical to the chromosomes that began? What is different? There are two chromosomes instead Of 4 (1/2 the number of parent cell) The chromosomes do not have a matched (homologous) pair

IN MALES… These 4 cells would be SPERM cells Sperm cells have tails so they can swim to find the egg Made in the TESTES

IN FEMALES… One cell would be very large…receive most of the cell material so that if fertilized it can support developing offspring The other 3 (polar bodies) are so small they die The egg doesn’t move Made in the OVARIES

In Conclusion… Meiosis is the process by which sex cells are produced. Meiosis reduces the number of chromosomes in sex cells to half the normal number Meiosis keeps the number of chromosomes from doubling when offspring are produced.

What are the similarities and differences between mitosis and meiosis? Complete web simulations on my pbworks page Complete worksheets Prepare a Venn Diagram…use the SEPUP simulation You may use students’ responses to Procedure Step 11 for a Quick Check to monitor their understanding of mitosis and meiosis. For more information on having this class discussion see the Teacher’s Edition for this activity.

How do chromosomes divide during the formation of egg and sperm cells? Revisit the Challenge How do chromosomes divide during the formation of egg and sperm cells? Students should be able to explain meiosis, including specific details about meiosis I and II. See the Teacher’s Edition for this activity for more information.

chromosome crossing over daughter cell DNA gametes gene meiosis Key Vocabulary chromosome crossing over daughter cell DNA gametes gene meiosis mitosis parent cell See Teacher Resources III: Literacy for more information on key vocabulary and the most effective strategies to enhance student vocabulary learning. Note that bold words are formally defined in this activity. Words in regular font are used in the activity, but not formally defined. The definition of a key vocabulary word should not be discussed as a class prior to the formal definition being introduced.