Biology Assignment 25

Cell Division:

Experiment Instructions

LEARNING GOALS

By the end of this unit, you should be able to do the following:

1. Describe the phases of Interphase and Mitosis and the key event that

occurs during each phase.

2. Identify the phases of Meiosis I that differ from Mitosis and the key

event that differs.

3. Identify which phase of Mitosis a fish or onion cell is in from a

microscope picture.

4. Identify which phase of Mitosis or Meiosis a cell is in from a bead

picture.

MATERIALS NEEDED

Two small bowls or tupperware containers (Nucleus)

Two colors of yarn, pipe cleaners, wire, or straws (Chromosomes)

Two pieces of paper (Cytoplasm and Plasma Membrane)

There is no report, but there is a worksheet to fill out. You will need to

take pictures of each stage of Interphase, Mitosis, and Meiosis to put in

the worksheet. TAKE PICTURES. Put a label for the phase into the

picture so you know which phase you have photographed.

You will be using yarn or other materials to simulate chromosomes during

the various stages of the cell cycle. Follow the pictures below and use your

own materials to mimic the phases.

SETUP (Demonstration)

1. The picture below shows example materials for this demonstration.

Your yarn, pipe cleaners, or whatever you chose to be your

chromosomes needs to have two long strands and two short strands

of each color. Ex. You need two long and two short strands of blue

yarn and two long and two short strands of red yarn. The long

strands of both colors should be equal length, as should the short

strands.

3. Set aside one of each chromosome (yarn) so that you have four

pieces on the table.

4. Put the chromosomes inside one bowl and cover with the other

bowl. This way you cannot see individual chromosomes, just like in

real interphase. Slide the pieces of paper together. This is the

starting state.

INTERPHASE (Demonstration)

G1 - The cell grows. Slide the pieces of paper apart.

S - The DNA is replicated. Add to the nucleus the four sister chromatids

that were held aside. Leave one or two hanging out so that you know you

replicated the DNA.

G2 - The cell grows a little more and confirms that all chromosomes were

copied. Count out your chromosomes one more time to simulate the cell

counting, and slide the papers a little farther apart.

MITOSIS (Demonstration)

Prophase - The chromosomes condense (become visible). Take off the bowl

covering your nucleus. (Note - This is not the nucleus breaking down; it's

simply a way of showing the chromosomes that were hidden before.)

Prometaphase - The nuclear envelope breaks down. Dump the

chromosomes into a pile on your paper.

Metaphase - The chromosomes line up along the center of the cell. Match

the sister chromatids (yarn of the same length and color) together and line

them up. The chromosomes must lie along the spot where the two pieces of

paper overlap. (Note - Sister chromatids were attached to each other way

back in S phase. Our model isn't good enough to do that.)

Anaphase - Sister chromatids separate. Move the sisters towards opposite

ends of the paper.

Telophase - Nuclei reform. Put the two sets of chromosomes into two

different bowls. (Note - Cytokinesis may be shown by separating the two

sheets of paper. Remember that this event could have begun as early as

Anaphase and that it is not a key event of any phase.)

Observations - Compare your cells now to the cell you had back before G1

began. Notice that you have the same number of chromosomes (four) in

each cell and that they are both the size of one sheet of paper.

Practice - Repeat the steps until you can do the actions and also recite the

key event of each stage from memory.

MEIOSIS (Demonstration)

To run meiosis, first start at the steps of Interphase. Interphase occurs the

same way regardless of if the cell is going through mitosis or meiosis.

Prophase I - The chromosomes condense and crossing over occurs. Remove

the second bowl. Use scissors and tape to cut off a small portion of one long

"red" strand and one long "yellow" strand and swap them. Leave the other

long sister chromatids alone. You can do this crossing over with the short

strands as well.

Prometaphase I - The nuclear envelope breaks down. Dump the

chromosomes into a pile on your paper.

Metaphase I - The chromosomes line up as homologous pairs along the

center of the cell. Match the sister chromatids (yarn of the same length and

color) together and also the homologues (the long "red" and long "yellow"

sister pairs are a homologous pair). The chromosomes must lie along the

spot where the two pieces of paper overlap. (Note - Compare this

arrangement to what you did in metaphase of mitosis. How is it different?)

Anaphase I - Homologues separate. Move the two sets of long strands to

opposite ends of the paper. Do the same with the short strands. (Note -

Compare this to what you did in anaphase of mitosis. How is it different?)

Telophase I - Nuclei reform. Put the two sets of chromosomes into two

different bowls. (Note - Cytokinesis may be shown by separating the two

sheets of paper.)

MEIOSIS II

Continue with Meiosis II as if you were simply running mitosis in these two

cells. DO NOT go through Interphase again. Start immediately with

Prophase II.

You MAY NOT use the same pictures you used for Meiosis I! The steps

are identical to Mitosis except you have half the number of chromosomes!

(You may not use your pictures of Mitosis either. Take new pictures!)

Observations - Compare your cells now to the cell you had back before G1

began. Notice that you have the half the number of chromosomes (two) in

each cell and that they are half the size of the original cell. Instead of having

a long "yellow" and a long "red," each cell only has one long

chromosome. The same with the short chromosome. This is the difference

between two of each chromosome (diploid) and one of each

(haploid). Combining any two of the haploid calls you made would result in

a diploid cell again.

Practice - Repeat the steps until you can do the actions and also recite the

key event of each stage from memory.

WORKSHEET #2

Your first worksheet required identifying the phases of mitosis in

microscope slides. The next worksheet is a template for you to insert

pictures of your Interphase, Mitosis, and Meiosis phases. Remember to also

fill in the key events.