WORKSHOP #7

MITOSIS, MEIOSIS AND GAMETOGENESIS

I.    SIMULATIONS

    A.    Preparations

             1.    Using two templates and sets of chromosomes from the lab guides, set up two identical parent cells as they would look in the G-2 phase prior to cell division.
             2.    Make each cell heterozygous for both the B/b and R/r genes.  Check to see that they are genetically identical (carry the same alleles).
             3.    Record them in the large cells of Figures 1 and 2.

     B.    The Cell Divisions.  With one cell, you will carry out a mitosis simulation; with the other, a meiosis simulation.

            1.    For each cell arrange the chromosomes as they would be situated during prophase in mitosis and meiosis 1, respectively.
                    a.    Are there any differences? Explain.
                    b.    Briefly define the terms, synapsis and tetrad.
            2.    Now arrange the chromosomes as they would appear in metaphase.
                    a.    Describe their positions.
                    b.    Are there any differences?

Mitosis figure

Fig. 1 Mitosis
 

Meiosis figure
Fig. 2 Meiosis
 

             3.    Now simulate the chromosome movements during anaphase for each cell using the parent cell outlines.
                      a.    Describe the similarities for the two cells.
                      b.    Describe the differences.
             4.    Place the chromosomes in the daughter cells on the templates as they would be distributed by the end of telophase.
              a.    Draw the results in Figures 1 and 2.
              b.    How many chromosomes are in the daughter cells for:

                        Mitosis ________ Single or double?
                        Meiosis 1 _______ Single or double?

              c.     Compare the genetic makeup of (alleles present in) daughter cells from the two types of cell division:

                        Mitosis:  identical alleles?
                                 list the alleles in the two daughter cells as a genotype.
                        Meiosis 1: identical alleles?
                                 list the alleles in the two daughter cells as a genotype.

             5.     Now place the contents of one daughter cell from the meiosis division onto the parent cell template.  Record the appearance in Fig. 3.
             6.     Arrange the chromosomes as they would line up in metaphase of the Meiosis 2 (M-2) division.

M-2 Division figure
Fig. 3   Simulation of M-2 Division

             7.     Simulate the chromosome migration during anaphase-2.
                      a. How does M-2 anaphase compare with M-1 anaphase?
                      b. How does M-2 anaphase compare with anaphase of mitosis?
             8.     Place the chromosomes from the parent cell of the template onto the daughter cells.  Record the results in Fig. 3.
                      a.    Compare the genetic makeup of the two daughter cells you created by writing out the genotypes.
                      b.    If the other daughter cell from the M-1 division (see Fig. 2) had been used to do the M-2 simulation, what would be the genotypes of the resulting cells?
                      c.     In the two meiotic divisions of one original parent cell, how many different genotypes are there among the four daughter cells?
             9.     Explain why you do or don't agree with this statement? "The daughter cells produced in the meiotic divisions would change shape, grow tails, and become sperm.
             10.    Reassemble a diploid parent cell on the template which is identical to the ones you started with in Fig. 1. Record the results in Fig. 4.

M-1 Division figure
Fig. 4   Alternate Simulation of M-1 Division

         11.     Carry out an M-1 meiotic division so that the combination of alleles in the daughter cells is different from that in your first simulation.  Record the results in Fig. 4.
                  a.     What is the probability that this would be the outcome rather than the results of your first simulation?
                  b.     What would the genotype of the gametes be after the M-2 division?
                  c.     A cell that is heterozygous for two genes can produce gametes with how many different genotypes? List them from your own simulations.

II.    OOGENESIS IN Ascaris: Use Fig. 5 to complete the following.

         1.     The stages in oogenesis have been scrambled in the diagram.  Use your lab notes to organize them in sequence by arranging the letters in order with arrows between them.
         2.     Give a short descriptive phrase or title under each figure within the diagram to explain what stage it illustrates.
         3.     Label the following:
                  a.    On A:  tetrads, fertilization membrane, sperm nucleus, shell.
                  b.    On B:  first polar body, egg cell membrane.
                  c.    On C:  spindle, migrating chromosomes, first polar body.
                  d.    On D:  sperm and egg pronuclei.
                  e.    On E:  stage of each cell in the figure.
                  f.    On F:  egg nucleus, sperm, food vacuoles.
                  g.    On G:  spindle, part of cell which will give rise to lst polar body.
                  h.    On H:  sperm nucleus, first polar body.
                  i.    On I:  first and second polar bodies.
                  j.    On J:  first and second polar bodies, cleavage furrows, migrating chromosomes.

Ascaris Reproduction
Fig. 5   Stages in Ascaris Reproduction

         4.        a.    What are polar bodies?
                    b.    Why are they produced in oogenesis but not spermatogenesis?
         5.        a.    What is the difference between sperm penetration and fertilization?
                    b.    Describe the time relationship between them.
         6.    Complete the Data Matrix below so the stages are in order, from earliest to the latest.  The matrix emphasizes diagnostic features that let you positively identify each stage.  One row has been filled out as an example.
 

DATA MATRIX 1.    Diagnostic Features of the Stages in Ascaris Reproduction

Stage     Letter   Name of Stage                          Diagnostic Features

1.             F                 unfertilized egg & sperm        sperm outside egg; no fertiliz.
                                                                                 membrane; I nucleus in egg;
2.

3.

4.

5.

6.

7.

8.

9.

10.
 
 

         7.     In which stage can we first say that a zygote has been formed? Explain.
         8.     a.     Which two of the drawings in Fig. 5 are not really part of oogenesis?
                 b.     They are stages in what process of development?

III. FERTILIZATION AND CLEAVAGE

The cell in Fig. 6 was formed when an egg nucleus and a sperm nucleus came together.  Use it to answer the following questions.
         1.     This kind of cell is called a ____________________.
         2.     The event which got "the sperm into the egg initially is called ___________________.
         3.     The event that occurred to bring the genetic material of the sperm & egg in close relationship as shown in Fig. 6 is called __________________.

Sperm & egg cell
Fig. 6   __________________ (title)

         4.     For this cell to begin developing into a multicellular organism, what process must occur next?
         5.     If the egg carried the "G" allele for the G/g gene, but the "t" allele for the T/t gene, what was the genotype of the sperm?
         6.      a.     Based on chromosome structure and number only, in what period of interphase is the cell as it is drawn (G-1, S, or G-2)? How can you tell?
                  b. For cell division to occur in this cell, what changes would have to take place first? Sketch the changes on Figure 6.
                  c.     Give a title to Fig. 6

IV.  CHECK ON MASTERY

 A.     Review.  Working with a study partner, review your answers to the questions. Check with your instructor if you are unsure about an answer.

B.    Multiple Matching.  Each of the numbered statements below applies to one or more of the eight processes (a-h) in the following list.  After the statement, give the letter for each process to which the statement applies.  Note that some statements may apply to two or more processes.  Item # 1 is given as an example.
                  a)     cytokinesis
                  b)     fertilization
                  c)     meiosis - 1
                  d)     meiosis - 2
                  e)     mitosis
                  f)     oogenesis
                  g)     spermatogenesis
                  h)     sperm penetration

         1.     Synapsis forms tetrads during prophase: c, f, g.
         2.     A second polar body is extruded from the cell.
         3.     The centromeres break and sister chromatids migrate to opposite poles.
         4.     One gamete enters the cytoplasm of another, different gamete.
         5.     The cytoplasm begins to pinch in at the equator of the cell.
         6.     The daughter cells from the division are about equal in size.
         7.     A spindle forms.
         8.     A new diploid cell forms from the union of two haploid cells.
         9.     The daughter cells have half as much DNA as the parent cell, but carry all the alleles of the parent.
       10.      The daughter cells are genetically identical to one another but not to the parent cell.
       11.      The daughter cells are genetically different from one another and from the parent cell.
       12.      Four gametes are formed from one parent cell by this process.

C.    Relationships.  State one or more relationships between each pair of terms by drawing a small concept map.  Be as specific as you can.
         1.    fertilization and zygote.
         2.    gametogenesis and spermatogenesis.
         3.    chromatids and tetrads.
         4.    meiosis-1 and first polar body.
         5.     haploid and diploid.
         6.     mitosis and meiosis.
         7.     independent assortment and alleles.
         8.     cytokinesis and meiosis.
         9.     mitosis and cleavage.
       10.     egg and pronucleus.
       11.    chromatids and chromosomes.

D.     Scholarly Definitions: Evaluate the definitions in 1-10.  Circle any items that are incorrect and change the words to make them correct.  Write TRUE if all information is already correct.

         1.     Polar body: a tiny cell produced by both M-1 and M-2 divisions in spermatogenesis; contains one-half of the parent cell's DNA, but little of its cytoplasm; develops further to form a gamete.

         2.     Cleavage: includes mitosis plus cytokinesis; results in daughter cells which differ genetically; if repeated several times can transform a zygote into a multicellular ball; one of the earliest stages in the development of a multicellular organism.

         3.     Diploid: the condition of gametes only; the remainder of our cells are haploid; having two alleles for each gene; twice as many alleles present as compared to the haploid condition.

         4.     Law of Independent Assortment: talks about distribution of alleles in formation of gametes; indicates that alleles on different chromosomes tend to be inherited together as pairs; applies only to genes located on different chromosomes.

         5.     Meiosis-2: produces a polar body in oogenesis; the formation of tetrads occurs in prophase; centromeres break and chromatids migrate in anaphase; daughter cells from the division are genetically identical.

         6.     Oogenesis: means the origin of an ovum or egg; occurs in the ovaries before ovulation; occurs through two mitotic divisions; produces one egg for each cell that starts the process.

          7.     Meiosis-1: occurs in oogenesis but not spermatogenesis; reduces the number of chromosomes to make the daughter cells haploid; breaks in the centromeres occur at the start of anaphase; produces a polar body in oogenesis.

         8.     Gametes: eggs and sperm; haploid; produced in ovaries and testes; one is mobile while the other stores food for early development; coming together involves sperm penetration and fertilization.

         9.     Spermatogenesis: occurs in the epididymis; four sperm are produced for each cell that begins the process; involves two meiotic divisions; two polar bodies are produced; is exactly the same as oogenesis; products of the process are haploid cells.

     10.     Fertilization: the coming together of two diploid gametes to form a haploid zygote; occurs before sperm penetration; happens in the oviducts of the female; involves the physical union of the genetic material of the gametes.

E.    Mitosis vs. Meiosis.  Answer the questions below to check your understanding of how mitosis and meiosis compare.

         1.     Contrast the behavior of chromosomes in the following stages of mitosis and meiosis:
                  a.     prophase M-1 vs. prophase of mitosis.
                  b.     anaphase M-1 vs. anaphase of mitosis.
                  c.     anaphase M-2 vs. anaphase of mitosis.
                  d.     anaphase M-2 vs. anaphase of M-1.

         2.     The daughter cells of the first meiotic division have half as much genetic material as the parent cell.  The same is true after a mitotic division.  There is a big difference, however.  What is it?

         3.     Immediately after the second meiotic division, how much genetic material remains in the daughter cells compared to the parent cell?

         4.     True or false?: The daughter cells following the first meiotic division are genetically identical (carry the same alleles).  Explain your answer.

         5.     When does DNA replication occur for meiosis as compared to mitosis?

         6.     What is the number of chromosomes for human cells in each of the following stages? Indicate if they are single or double chromosomes.
                  a.     prophase of mitosis.
                  b.     telophase of mitosis after cytokinesis.
                  c.     telophase of meiosis 1 after cytokinesis.
                  d.     telophase of meiosis 2 after cytokinesis.

         7.     In your own words, summarize the process of meiosis without using names of the phases.  Compare your summary with that of a study partner.
 

Chromosome Models
 

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