The Case of the Dividing Cell: Mitosis and Meiosis in the Cellular CourtFile

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The Case of the Dividing Cell: Mitosis and Meiosis in the
Cellular Court
Part I—The First Day of Testimony
by
Clyde Freeman Herreid
Department of Biological Sciences
University at Buffalo, State University of New York
Mitosis Exposed
“Hear ye. Hear ye. The Honorable Judge Cellular now presiding. All rise.”
The judge in his black robes came silently into the courtroom amid the usual bustle
that attended one of the special sessions. He slid into his high backed chair, glanced at
the papers on the bench before him, and as was his habit, he gazed first at the
defendant over his spectacles. Then giving the same attention to the prosecution, he looked over the
jury. If he could have pursed his lips, he would have done so, for he wondered greatly at this particular
jury that was filled with prokaryotic cells.
Prokaryotic cells? It hardly seemed fitting that they would be sitting in judgment of a eukaryotic matter.
Hardly fitting at all. Oh, well, both the prosecution and the defense seemed to want it that way. So be it.
He knew that the attorneys wanted to be impartial, but this was unseemly. Prokaryotes, what did they
know about eukaryotes? Harrumph.
The judge adjusted his plasma membrane over his shoulders and began speaking with a voice that
seemed to resonate from the bowels of his endoplasmic reticulum. “Ahem, let us see now. This is the
case of the State vs. Egg Cell Number 6624223. This presents an unusual situation involving an alleged
capital offence. The defendant is charged with being an undesirable mutant in the body politic. The
penalty is death. This is the most serious of matters. It requires our undivided attention. So let us begin,
but let us begin with the presumption of innocence. Please, now councilors, let us have the opening
statements. But, please keep your comments brief and to the point. The prosecution first, arguing the
position for the State. I believe it is Ms. Liv, is it not?”
“Yes, thank you, Your Honor. Members of the jury, I come to you today as a member of our cellular
community. I come from a long line of cells that stretches back to a time when the world was once filled
with only prokaryotic cells like yourselves. For over a billion years you ruled the world. We eukaryotic
cells are but recent upstarts. For the most part we live in colonies making up the bodies of animals,
plants, and fungi.”
“I, in fact, am a liver cell, one of several trillion cells living in a human I’ll call Martha. It is essential
that we all live in harmony with one purpose in life—that is, survival. If Martha doesn’t survive, we all
die—I, and the rest of the liver cells, the kidney cells, the muscle cells, the nerves, and all of the others
that make up this grand human being.
“Yet, this is not all. Our individual survival is only part of the story. We would not be here except for
the fact that we all are descendents of untold numbers of other organisms, many of them complex
colonies of cells, for the last 700 million years. And we have relied on sex. Yes, I know that this concept
is one that you asexual cells hardly understand. But as you have certainly read, in humans, like Martha,
the cells in her ovary produce some unusual cells called eggs. And in Martha’s husband there are some
cells called sperm. If these two cells get together they will produce a fertilized egg that may grow up to
be another colony of cells we call a baby.
“Now the point of all of this is that in order to produce a perfect baby, the sperm and the egg must be
perfect. This brings me to the central issue of this crime. The defendant on the stand today is one of
Martha’s cells. We all love Martha—some of us have lived with her for years—but as we will show, she
has been alive for 43 years and this has led to trouble. Many of her eggs are flawed. And this is exactly
the case with our defendant, Egg Cell Number 6624223. SHE IS NOT PERFECT. It is our contention
that she should be destroyed by apoptosis. She is not just contaminated by a simple point mutation. She
is disfigured by having an extra chromosome 21. This invariably leads to Down Syndrome. She should
be destroyed so that a pure lineage can go on. We believe that you will see the wisdom of this solution
by the end of the trial and trust in your good judgment.”
“Thank you, Ms. Liv. Now, Councilor Oocyte, would you give your opening remarks?”
“Thank you, Your Honor. Cells of the jury, you have heard the remarks of my colleague. She argues that
my client is flawed. She bases that on unsound logic. We will stipulate that my client is unusual, but that
does not mean she is flawed or damaged. In every part of Martha’s body there are unusual cells. Some
cells in the lining of her digestive tract are triploid or have even higher numbers of polyploidy. Her liver
cells, and perhaps Ms. Liv herself, are filled with unusual numbers of chromosomes. Some have three,
four, five, six, seven, or more sets of chromosomes. Ms. Liv here appears in the pink of health! What’s
there to be troubled about? These cells are all living healthy lives and contributing to Martha’s welfare.
There is hardly a reason to get upset with my client who has a single extra chromosome 21. And, as is
well known, even if a Down baby is the result, these children live happy, wholesome lives. We will
clearly demonstrate to the jury that death is hardly a reasonable remedy, and that, in fact, there is no
crime that has been committed at all.”
“Thank you, councilor. Now Ms. Liv, you may call your first witness.”
The First State Witness: Mr. Nuclear Membrane Explains the
Secrets of Mitosis.
“Your Honor, I call Mr. Nuclear Membrane of the Epidermis to the stand.”
“Bailiff, administer the oath.”
“Do you swear to tell the truth, the whole truth, and nothing but the truth so help you DNA?”
“I do.”
“I am calling Mr. Nuclear Membrane here as an expert witness on the process of cell division.”
“I object Your Honor. Mr. Nuclear Membrane cannot serve in this capacity, as he is simply an expert in
the topic of cell division that occurs in skin cells. This is hardly the same as that which occurs in the sex
cells. And that is the subject of the case. Although cell division in the skin cells is just like cell division
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almost everywhere else in the body, cell division is entirely different in the ovaries and the testes where
the sex cells are manufactured. The skin cells divide by mitosis. The sperm and eggs are produced by
meiosis—an altogether different process.”
“Ms. Oocyte objects. Councilor Liv, what do you say?”
“I am not calling Mr. Nuclear Membrane as an expert in meiosis but as one on mitosis. I wish to lay the
groundwork for making the distinction between the two.”
“Then I withdraw my objection, Judge, and will so stipulate that the gentleman is
an expert in mitosis and nothing else. Go ahead, this should be interesting.”
“Now, Mr. Membrane, please describe the events of simple cell division that
occurs in the skin. I believe you have some diagrams to show the jury that will
help. Bailiff, would you please place the exhibits on the easel?”
“Yes, Ms. Liv, I do. First, I want to stress that the normal skin cell divides
repeatedly in its life. Skin cells are always being wiped away when Martha’s hands
rub against anything. We do indeed have a busy time keeping up with the wear and
tear of everyday living.
“When Martha’s cells get ready to divide, the genetic information has to be copied. You know what I
mean. If you’re going to make another cell just like yourself, you’ve got to make sure that the next
generation knows what to do; you’ve got to send the right information. Right? So the cell has to make a
copy of the instructions in the DNA—you know, the genetic material. So here’s the deal. The scientists
that study this stage in our life call it ‘Interphase,’ and that’s what’s shown in Exhibit A. This is the time
when we’re really livin’ it up, growing like crazy, making proteins like there’s no tomorrow, and
making little organelles. But then things change in a big way. The cell has gotten too big, you might say.
It’s got to divide. And that’s when the DNA makes a copy of itself.
“Now take a look at the diagrams that show the next steps. All of ’em have special names. There’s early
and late Prophase, Metaphase, Anaphase, and my favorite, Telophase.”
“Please, tell us the overall gist of what is happening.”
“Well, it’s no mystery. Look here at Exhibit B. The DNA that has made an extra copy of itself gets all
wrapped up into wads you call chromosomes. But each chromosome has two parts, you know, the
original part and the copy. They’re called chromatids—the parts, that is. The two parts of each
chromosome are linked together at a point in their middles.
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“So, what happens next?”
“Well, in Exhibit C you see the chromosomes lining up in the center of the cell, and then in Exhibit D
the pairs of chromatids split apart and go off to opposite sides of the cell. They’re pulled there by fibers.
All of the chromosomes are doing the same thing, all at once. Half of their chromatids go to one side
and half go to the other. That way, each side of the cell gets a complete set.”
“Just a moment, Mr. Membrane, where did these fibers come from? It looks like they come from the
centrioles.”
“That’s right, but I’m not quite sure as I never have really been around to see that part of the story. I’ve
been told that…”
“Objection. That’s hearsay, Your Honor.”
“Objection sustained.”
“Let’s try this again, Mr. Membrane. What have you seen yourself?”
“The chromatids are separated and dragged to the opposite sides of the cell, and that’s when I
reappear—see, that’s me, right here in Exhibit E—in two places, actually. I make a nuclear membrane
that surrounds the chromosomes on both sides of the cell. You know, that’s my job, to surround the
DNA for the two new cells. I’m making two nuclei for the next generation of cells.”
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“Let me be sure I have this right. The chromosome material—the DNA—makes a copy of itself, then
bundles itself up so it can move to the center of the cell more easily. The two copies of the DNA are
wound into separate bundles called chromatids that are bound together. They line up in the center of the
cell and then become separated by some fibers that seem to pull them apart. So one set of chromatids (I
presume you call them chromosomes at this point) goes to one side of the cell and the other set goes to
the other side of the cell.”
“That’s right. You see, when the cell starts to divide, that is, when the cytoplasm in the center of the cell
begins to pinch off the two parts, both sides get a complete set of chromosomes. In humans, there are 46
chromosomes. So every time a skin cell makes a copy of itself, both cells get a complete set of 46
chromosomes. Then each cell reverts to Interphase. It’s wonderful, don’t you think?”
“Yes, I do. Thank you for your testimony. Now councilor Oocyte, the witness is yours for cross
examination.”
Ms. Oocyte Cross Examines
“Thank you, Judge. Now just to be sure I have this right, Mr. Nuclear Membrane, do I understand that
you disappear during this process and reappear at the end?”
“That’s right. I have to sort of break apart in the early Prophase so that the chromosomes can move to
the center of the cell. They couldn’t do this if I were in the way, could they?”
“No, I don’t suppose they could, Mr. Nuclear Membrane. Then the next time you see anything is when
you reassemble around the two new sets of chromosomes on opposite sides of the cell. That’s the reason
Telophase is your favorite time, isn’t it? So everything else you have told us about in between these two
times is mere scuttlebutt, isn’t it?”
“I would hardly call it that. It is well known that…”
“Let’s move on to another question, shall we? Tell me, when the DNA makes a copy of itself, is the
copy always perfect?”
“Well, you know…, most of the time. It has to be…, otherwise the cell might be sick, become cancerous
or something.”
“But that isn’t what always happens, is it?’
“Ah…, no. I guess not.”
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“Isn’t it true that many cells have so-called ‘imperfect copies’ of DNA during mitosis and things aren’t
disastrous? In fact things are often pretty good, aren’t they? Sometimes these somatic mutations turn out
well. I’m thinking of cases where a hair cell on the head of a person like Martha mutates and the person
has a nice stripe of white running through their hair. That’s pretty striking, isn’t it? You wouldn’t say
that is bad would you? Or abnormal? Or a reason to destroy Martha or her mutant cell? No? I thought
not, it depends upon the situation, doesn’t it?”
“Yes, I guess so.”
“No further questions, Your Honor.”
“You may step down, Mr. Nuclear Membrane. And I believe we have had enough testimony for today.
We will resume tomorrow at the same time. Court is in recess.”
Questions
1. What are the major events that occur during each of the stages in the life cycle of a cell such as a
skin cell, i.e., Interphase, Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis? Assume
you are a court reporter that has to explain these stages to your readers with as little jargon as
possible.
2. How does cell division differ in prokaryotes and eukaryotes? Clearly, these differences may be
difficult for the prokaryotes in the jury to follow unless you show the similarities and differences.

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