Experiment 3: Following Chromosomal DNA Movement through Meiosis

Experiment 3: Following Chromosomal DNA Movement through Meiosis

Materials 2 Sets of Different Colored Pop-it® Beads (32 of each - these may be any color) (4) 5-Holed Pop-it® Beads (used as centromeres)

Procedure:

Trial 1

As prophase I begins, the replicated chromosomes coil and condense…

1. Build a pair of replicated, homologous chromosomes. 10 beads should be used to create each individual sister chromatid (20 beads per chromosome pair). The five-holed bead represents the centromere. To do this...
1. Start with 20 red beads to create your first sister chromatid pair. Five beads must be snapped together for each of the four different strands. Two strands create the first chromatid, and two strands create the second chromatid.
2. Place the five-holed bead flat on a work surface with the node positioned up. Then, snap each of the four strands into the bead to create an "X" shaped pair of sister chromosomes.
3. Repeat this process using 20 new beads (of a different color) to create the second sister chromatid pair. See Figure 6 (located in Experiment 2) for reference.
2. Assemble a second pair of replicated sister chromatids; this time using 12 beads, instead of 20, per pair (six beads per each complete sister chromatid strand). Snap each of the four pieces into a new fiveholed bead to complete the set up. See Figure 7 (located in Experiment 2) for reference.
3. Pair up the homologous chromosome pairs created in Step 1 and 2. DO NOT SIMULATE CROSSING OVER IN THIS TRIAL. You will simulate crossing over in Trial 2.

1. Configure the chromosomes as they would appear in each of the stages of meiotic division (prophase I and II, metaphase I and II, anaphase I and II, telophase I and II, and cytokinesis).
2. Diagram the corresponding images for each stage in the sections titled “Trial 1 - Meiotic Division Beads Diagram”. Be sure to indicate the number of chromosomes present in each cell for each phase.
3. Disassemble the beads used in Trial 1. You will need to recycle these beads for a second meiosis trial in Steps 7 - 11.

Trial 1 - Meiotic Division Beads Diagram

Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase II

Metaphase II

Anaphase II

Telophase II

Cytokinesis

Trial 2

1. Build a pair of replicated, homologous chromosomes. 10 beads should be used to create each individual sister chromatid (20 beads per chromosome pair). The five-holed bead represents the centromere. To do this...
1. Start with 20 red beads to create your first sister chromatid pair. Five beads must be snapped together for each of the four different strands. Two strands create the first chromatid, and two strands create the second chromatid.
2. Place the five-holed bead flat on a work surface with the node positioned up. Then, snap each of the four strands into the bead to create an "X" shaped pair of sister chromosomes.
3. Repeat this process using 20 new beads (of a different color) to create the second sister chromatid pair. See Figure 6 (located in Experiment 2) for reference.
2. Assemble a second pair of replicated sister chromatids; this time using 12 beads, instead of 20, per pair (six beads per each complete sister chromatid strand). Snap each of the four pieces into a new five-holed bead to complete the set up. See Figure 7 (located in Experiment 2) for reference.
3. Pair up the homologous chromosomes created in Step 8 and 9.
4. SIMULATE CROSSING OVER. To do this, bring the two homologous pairs of sister chromatids together (creating the chiasma) and exchange an equal number of beads between the two. This will result in chromatids of the same original length, there will now be new combinations of chromatid colors.
5. Configure the chromosomes as they would appear in each of the stages of meiotic division (prophase I and II, metaphase I and II, anaphase I and II, telophase I and II, and cytokinesis).
6. Diagram the corresponding images for each stage in the section titled “Trial 2 - Meiotic Division Beads Diagram”. Be sure to indicate the number of chromosomes present in each cell for each phase. Also, indicate how the crossing over affected the genetic content in the gametes from Trial 1 versus Trial 2.

Trial 2 - Meiotic Division Beads Diagram:

Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase II

Metaphase II

Anaphase II

Telophase II

Cytokinesis

1. What is the state of the DNA at the end of meiosis I? What about at the end of meiosis II?
2. How are meiosis I and meiosis II different?
3. Why do you use non-sister chromatids to demonstrate crossing over?
4. What combinations of alleles could result from a crossover between BD and bd chromosomes?
5. How many chromosomes were present when meiosis I started?
6. How many nuclei are present at the end of meiosis II? How many chromosomes are in each?
7. Identify two ways that meiosis contributes to genetic recombination.
8. Why is it necessary to reduce the number of chromosomes in gametes, but not in other cells?
9. Blue whales have 44 chromosomes in every cell. Determine how many chromosomes you would expect to find in the following:
   Sperm Cell:
   Egg Cell:
   Daughter Cell from Mitosis:
   Daughter Cell from Meiosis II:
10. Research and find a disease that is caused by chromosomal mutations. When does the mutation occur?
11. What chromosomes are affected? What are the consequences?
12. Diagram what would happen if sexual reproduction took place for four generations using diploid (2n) cells.