Lab

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Meiosis

Experiment 1: Following Chromosomal DNA Movement through Meiosis

In this experiment, you will model the movement of the chromosomes through meiosis I and II to create gam-

etes.

Procedure Part 1: Modeling Meiosis without Crossing Over

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

1. Build a pair of replicated, homologous chromosomes

(Figure 3). 10 beads should be used to create each indi-

vidual sister chromatid (20 beads per chromosome pair).

Two five-holed beads represent each centromere. To do

this...

a. Start with 20 beads of the same color 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 with a 5-

holed bead at the center of each chromatid. This

creates an “I” shape.

b. Connect the “I” shaped sister chromatids by the 5-holed beads to create an “X” shape.

c. Repeat this process using 20 new beads (of a different color) to create the second sister chromatid

pair.

2. Assemble a second pair of replicated sister chromatids (Figure

4); this time using 12 beads, instead of 20, per pair (six beads

per each complete sister chromatid strand).

3. Pair up the homologous chromosome pairs created in Step 1

and 2. DO NOT SIMULATE CROSSING OVER IN THIS TRI-

AL. You will simulate crossing over in Part 2.

4. 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 Sets of Different Colored Pop-it® Beads (32 of

each - these may be any color)

8 5-Holed Pop-it® Beads (used as centromeres)

Materials

Figure 3: Bead set-up. The blue beads repre-

sent one pair of sister chromatids and the

black beads represent a second pair of sister

chromatids. The black and blue pair are ho-

mologous.

Figure 4: Second set of replicated chromo-

somes.

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Meiosis

5. 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.

6. Disassemble the beads used in Part 1. You will need to recycle these beads for a second meiosis trial

in Steps 7 - 12.

Part 1 - Meiotic Division Beads Diagram

Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase II

Metaphase II

Anaphase II

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Meiosis

Telophase II

Cytokinesis

Part 2: Modeling Meiosis with Crossing Over

7. Build a pair of replicated, homologous chromosomes. 10 beads should be used to create each individual

sister chromatid (20 beads per chromosome pair). Two five-holed beads represent each centromere. To

do this...

a. Start with 20 beads of the same color 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 with a 5-holed bead at the center of each chroma-

tid. This creates an “I” shape.

b. Connect the “I” shaped sister chromatids by the 5-holed beads to create an “X” shape.

c. Repeat this process using 20 new beads (of a different color) to create the second sister chroma-

tid pair.

8. 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.

9. Pair up the homologous chromosomes created in Step 8 and 9.

10. 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 chro-

matids of the same original length, there will now be new combinations of chromatid colors.

11. 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).

12. 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 Part1 versus Part 2.

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Meiosis

Part 2 - Meiotic Division Beads Diagram:

Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase II

Metaphase II

Anaphase II

Telophase II

Cytokinesis