BioLab3 Meiosis and Sexual Reproduction Lab Report Name, date, course and section required for password: The lab report is unique each semester and checks have been put into place to ensure students are doing their own work. Copying from other students or from outside resources will result in a zero on the accompanying lab quiz. I. Homologous Chromosomes 1. On a pair of homologous chromosomes, two alleles both code for blue eyes. Is this condition considered homozygous or heterozygous? 2. What does heterozygous mean? 3. What is the difference between diploid and haploid cells? 4. Based on Lab, Exercise 1, what do the letters F and B represent? II. Meiosis in Eukaryotes 1. At the end of meiosis II, are the resulting cells haploid or diploid? 2. Print the document found in Lab, Section 1. Use this document to follow along with Exercise 2 and draw the beads as they appear at the end of each stage of meiosis I and meiosis II. Sign and date your completed document and include with this lab report. III. Oogenesis and Spermatogenesis 1. What type of cells undergo meiosis? 2. Where does meiosis occur in human males and females? © 2016 Access Learning Systems SP22 1 3. After fertilization occurs, are the resulting cells diploid or haploid in chromosome number? IV. Summary of Mitosis and Meiosis 1. Compare mitosis and meiosis in the table below. Mitosis Meiosis Number of chromosomes in resulting cells Number of nuclear divisions V. Meiosis and Life Cycle 1. How many total chromosomes do frogs have? 2. How many pairs of chromosomes do frogs have? 3. Determine whether the following types of cells are haploid (1n) or diploid (2n). Type of cell Haploid or Diploid Body cell Sperm cell Egg cell Zygote Summary Questions 1. Distinguish between meiosis and mitosis. 2. If a horse has 64 chromosomes before meiosis, how many chromosomes would exist in each nucleus after meiosis I? After meiosis II? © 2016 Access Learning Systems SP22 2 3. Is meiosis I or meiosis II most like mitosis? Explain why. 4. Name the male and female gametes that are produced by meiosis. 5. A trait is given the alleles aa. It this homozygous or heterozygous? 6. Before mitosis begins one sister chromatid of a duplicated chromosome has the allele f, what allele will the other sister chromatid have? 7. What would happen if gametes were produced by mitosis instead of meiosis? 8. Differentiate between homologous chromosomes and sister chromatids. © 2016 Access Learning Systems SP22 3 Lab 10 – Meiosis and Sexual Reproduction EXERCISE 1 Construction of homologous chromosomes 1. Select twenty-four pop beads of one color and two magnets. Construct two strands of pop beads consisting of five beads of one color on one side of the magnet and seven beads of same color on other side of the magnet. Each colored bead represents a gene segment. Each strand represents a chromosome. The two strands represent a replicated chromosome (Figure 2). 2. Place a piece of tape with the letter F on the two top beads of one set and a letter B on the two bottom beads. Join these identical sections at their magnets representing the sister chromatids of a replicated chromosome (Figure 2). The magnets represent the centromere of the replicated chromosome. 3. Select a second color of pop beads. Construct the homologue to the replicated chromosome above. Construct the same size structure as the one in steps 1 and 2. Place a letter f on the top two beads of this set and a letter b on the bottom two beads of the set. Join this set by their magnets. 4. You have constructed a model of two replicated chromosomes that are homologous to each other. They have two gene positions along their length labeled F, B, or f, b (Figure 2). sister chromatids sister chromatids Figure 2 Model of Replicated homologous chromosomes EXERCISE 2 Modeling the stages of meiosis with pop beads Meiosis I begins with a nucleus that is diploid. The chromosomes are in their replicated state. Meiosis I has four stages: Prophase I, Metaphase I, Anaphase I, and Telophase I. 1. Place the strands of pop beads constructed in Exercise 1 on the lab table and draw a chalk circle representing the cell nucleus around the two sets of pop beads. During interphase the chromosomes are replicated and consist of two identical parts termed sister chromatids. The replicated chromosomes are randomly dispersed throughout the nucleus. Draw the pop beads during Interphase (Figure 4). Be sure to include the letters which represent the alleles. 2. Prophase I During this stage the nuclear envelope disassociates and the replicated chromosomes become condensed. The spindle apparatus will begin to extend toward opposite poles. The spindle apparatus can be represented with pieces of string as the spindle fibers and two X’s as the centrosomes. Prophase I is unique because homologous chromosomes pair with each other and intertwine as a tetrad. This pairing process is called synapsis. Using the 2 strands of each color bead representing the homologous pair, illustrate synapsis. During synapsis the non-sister chromatids exchange genes at the F and f positions. When gene segments are exchanged between non-sister chromatids of homologous chromosome pairs, it is termed crossing-over (Figure 3). Remove one color bead with the F and exchange with the other color bead f. In late prophase, the homologous chromosome pairs begin to move to the spindle equator as a tetrad and the spindle fibers attach to the centromeres. Tie a length of string to each of the two homologues at the centromere region. Draw the pop beads during prophase I (Figure 4). Include the letters indicating the alleles of each sister chromatid. Figure 3 Model of gene exchange between homologous chromosomes 3. Metaphase I The centromeres of each homologue are situated on opposite sides of the equator and spindle fibers attach each one to opposite spindle poles. Position the loose ends of the strings that are attached to each homologue at opposite poles. Illustrate this step of meiosis I with the pop beads. Draw the pop beads during metaphase I (Figure 4). 4. Anaphase I During anaphase I, homologous chromosomes separate and are pulled to opposite poles by the shortening of the spindle fibers. Each homologue still contains two sister chromatids. Demonstrate this step by pulling the strings attached to each homologue in opposite directions toward a pole marked with an “X” on your lab table. Draw the pop beads during anaphase I (Figure 4). 5. Telophase I Each homologue is now at its respective pole and cytokinesis is completed. Demonstrate this by drawing a chalk circle around each of the two homologues, or replicated chromosomes, representing the two cells formed by cytokinesis. Draw the pop beads during telophase I (Figure 4). The first meiotic division is complete. There are two daughter cells each containing one replicated chromosome consisting of two sister chromatids. The nucleus of each cell is now haploid. This is why meiosis is known as reduction division, reducing the number of chromosomes in the cells by half. Indicate the alleles on each of the chromatids in the 2 cells. Meiosis II occurs in each of the daughter cells that resulted from meiosis I which contain half the amount of chromosome material as the beginning cell nucleus. Meiosis II has four stages: Prophase II, Metaphase II, Anaphase II, and Telophase II. 6. Prophase II The sister chromatids are still attached by their centromeres. The spindle apparatus forms again and begins to migrate and spindle fibers attach to the centromeres. Draw the pop beads during Prophase II (Figure 4). Indicate the alleles on each of the chromatids. 7. Metaphase II The replicated chromosomes align along the equator, the centromeres lying on the equator. The spindle fibers attach each chromatid to opposite spindle poles. Draw the pop beads during metaphase II (Figure 4). Indicate the alleles on each of the chromatids. 8. Anaphase II The sister chromatids separate, moving toward the opposite poles. After the sister chromatids separate, each is an individual (not replicated) chromosome. Cytokinesis (cytoplasmic division) begins during anaphase II. Separate the two lengths of pop beads at the magnet and pull them toward opposite polls. Change the chalk circle so that it dips inward in the center to illustrate cytokinesis. Draw the pop beads illustrating anaphase II (Figure 4). Indicate the alleles on each of the chromatids. 9. Telophase II The two chromosomes are at opposite poles. The nuclear envelope forms around each set and cytokinesis is completed forming four cells. Four daughter nuclei now exist. Each nucleus contains one individual chromosome of the homologous pair originally present within the parental nucleus. Illustrate telophase with the pop beads, and with the use of chalk, complete the nuclear membrane around the beads and the plasma membrane of the new cells formed by cytokinesis. Draw the result of telophase II (Figure 4). Indicate the alleles in each cell. Interphase (2n) MEIOSIS I Prophase I Metaphase I Anaphase I Telophase I (Continued) * * Figure 4 Stages of meiosis (Meiosis continued) * MEIOSIS II * Prophase II Metaphase II Anaphase II Telophase II Figure 4 Stages of meiosis (continued) 01231004672689 711 1 112 31!2 9 9 1″19 0 01 212 Introduction of Meiosis I https://www.youtube.com/watch?v=U6gcga65vEE Prophase I https://www.youtube.com/watch?v=4K4nhPV_ghU Metaphase I https://www.youtube.com/watch?v=iPuF0QZSEGI Anaphase I and Telophase I https://www.youtube.com/watch?v=ITzHmGFGZq
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