SUBJECT: Analogies
DATE: 5/96; 1/97
In the fall, I'll be teaching cell
>biology to non-majors and I would like to incorporate more
>analogies in my presentations.
>
I've just finished marking genetics exams and I came across these two
analogies proposed by a student,
"Heterochromatin is like my wool sweaters in the summer - all neatly
and
tightly packed into my dresser drawer. Euchromatin would be like these
same sweaters in the winter - all loosely scattered around the floor of
my
room."
"Splicing mRNA is like me saying to my friend, "I'm so f$#%^@#*&
tired I
could just pass out". If I were speaking to my mom, I would just splice
out the f$#%^@#*& - same information, different form."
Tom Haffie Phone: 519-679-2111 (6502)
Department of Plant Sciences FAX: 661-3935
University of Western Ontario e-mail: thaffie@julian.uwo.ca
London, ON, Canada
N6A 5B7
My favorite analogies:
1. most connective tissues i.e. cartilage:
are like Jell-O (non-cellular matrix) with fruit cocktail (cells)
mixed in it
2. DNA is solution has the consistency of "baby snot" i.e. it
is thick
and viscous and if you were to stick a glass rod in it and then pull
it out the DNA stings along with the glass rod not unlike wiping a
baby's nose. I use this when discussing heating up of DNA in solution
as to break the hydrogen bonds and the solution becomes less viscous
(I find that if I can gross them out, they remember it!)
I have others but these are the two that I remember at the moment.
Jim Ingold
LSU-Shreveport, Louisiana
jingold@pilot.lsus.edu
My favorite analogy when discussing the semi-permability of a cell membrane;
The cell membrane is like the offensive line in football. It wants to let
the running back with the football out, without letting the defensive line
in...
The junior high boys love this...
Kirsten
University of Toledo
re: analogies
For covalent, polar and ionic bonds, think of sharing sweaters with a
sibling who wears the same size. Both of you want to wear a different
sweater each day of the week, but each of you has only 5. So if you
each share 2 of yours equally (covalent), both of you have a share in 7
sweaters. If one of you has extra sweaters and donates some to the
other (ionic), you both can have 7. If one of you if not playing fair and
takes the siblings sweaters more often than allows the sibling to use
them, you have unequal sharing (polar covalent bond).
For the difference between chromatin and chromosomes, think of a ball
or skein of yarn as you buy it from the store (wound up, as DNA in
chromosomes) and then what it is like after you let your pet cat play with
it (uncondensed, as in chromatin).
For glycolysis, finger-plays simulate the carbon chain. Glucose is three
fingers held up on each hand, hands held together. As a result of
glycolysis, the hands separate, yielding 2 hands, each with three fingers
up (3 C's). Continue folding down fingers for the decarboxylation
reactions that follow. Do the reverse for Calvin cycle; 5 fingers on one
hand plus 1 finger on the other is RuBP plus carbon dioxide, etc.
For electron transport chains and energy release as electrons pass
down carriers, think of a "hot potato" game, in which the heated
(high-energy) potato (electron) loses energy as it is passed from one
person (carrier) to another.
For n and 2n chromosomes in meiosis and fertilization, think of pairs of
socks and individual socks.
Hildy Sanders
Villa Julie College
Stevenson, MD 21153
Phone: 410-602-7303
Fax: 410-486-3552
I like Hildy's use of sweaters for illustrating the different types of
chemical bonds. But what I use most often is two students and one biology
textbook (lecture props that are already in the room). If two students
buy one biology book and they share it by having it every other day, then
you have an analogy for non-polar covalent bonding (equal sharing). If
two students buy one biology book and one of them hogs it by keeping it
for several days at a time, then you have an analogy for polar covalent
bonding (unequal sharing). If two students buy one biology book and one
decides it doesn't want to use the book, and relinquishes use of the book
to the other, then you have an analogy for ionic bonding (transfer of
electrons).
Obviously, students who share books have some sort of "bond" between
them!
Peter Petokas
Since we cover chemical bonding early in the semester, I give this question
to
non-majors as an ice-breaker after I've described ionic, polar covalent,
non-polar covalent, and hydrogen bonds:
If you and a "significant other" are atoms that are going to form
a bond, what
type of bond would you want to form, and why?
I let them discuss it in small groups for a few minutes, then ask people
to
volunteer their answers. There is always someone for every type of bond,
and
the explanations are great. On the next Ricki Lake...women who marry men
for
their electrons...
Many of my students are confused about binomial nomenclature, especially
how
the specific epithet fits into the rest of the classification hierarchy
since
having the same specific epithet doesn't give any information about the
relatedness of two organisms. I use an analogy with our first name/surname.
The genus is like the surname; it indicates relatedness. The first name
is
just a name your parents liked. I'm Dickey, Jean. When you meet me you might
ask if I'm related to someone you know with the same last name, like James
Dickey. But you wouldn't ask if I'm related to Jean DeSaix.
Jean Dickey
dickeyj@clemson.edu
In addition to using three fingers of each hand to represent the initial
6-C glucose, color your thumb and little finger with your overhead pen,
and you can show the phosphates popping on and off at the appropriate
times.
***************************************************************
Louise Baxter email: baxterl@cwu.edu
Department of Biological Sciences phone: 509-963-2745
Central Washington University fax: 509-963-2730
Ellensburg, WA 98926
I have lots of fun with analogies, especially when the metaphor can
be extended. For example, to give students some idea of how truly
extraordinary mitosis is, I tell them that if you made a scale model of
a
single DNA molecule found in the average human chromosome you would get
a
piece of spaghetti about 2 mm wide and 40 miles long. Yes, I know it should
be in kilometers, but it has more impact this way. Now imagine that you
have
92 pieces of such spaghetti (4n after S phase) and you have to divide them
up
into two exactly equal piles without breaking any of them in about an hour.
Cells are pretty smart! Another is used to visualize the recent brouhaha
in
immunology about the immune system recognizing self vs. nonself or danger
vs.
nondanger. Both sides must be right as any bank security guard knows. A
security guard must let in strangers (customers) without starting to shoot
people, just like the immune system can't mount a vigorous attack on those
foreign carrot proteins you just ate. But when a robbery is in progress
and
the alarm sounds, the guard should be suspicious of anyone he doesn't know
and be careful not to shoot the tellers. The immune system similarly goes
on
high alert but must not attack its own cells (unless they are committing
treason by serving as a factory for replication of viruses) when tissue
damage signals an infection. Sometimes the immune system can be fooled by
false alarms (tissue damage due to a sprained ankle, invasion by ragweed
pollen) just like a poor guard can be fooled by a bell at an adjacent school,
and must be restrained with ice packs or antihistimines.
Perhaps my favorite graphic example is used to show the power of
ruling out alternatives as opposed to accumulating evidence for something.
I bring my stuffed rhinoceros to class and claim the he is a dog, and that
I'm going to prove it. After all, it has two ears, two eyes, four legs,
a
mouth, two nostrils and a tail just like a dog. With that much evidence
in
favor of him being a dog, how could I be wrong? Of course the horn instantly
rules out my "model" as the students immediately see. Getting
them to use
the same method in more complex situations is still hard, but when they
come
into my office and see my rhino they ask how my "dog" is doing.
Some have
remembered the demonstration years later.
Jim Eliason
Manhattan College/College of Mount St. Vincent
Biology Dept.
jeliason@mcs1.mancol.edu
To clarify my earlier post about the rhino that I "claim" is a
dog, the
rhino (I call him Gregor) is a foot long toy, not a taxidermy project. He
has given me some fun on two other occasions. Once, to underscore my point
in an unintentional fashion, one of my colleagues (One of the famous Blind
Men???) who saw Gregor only from the rear asked me what I was doing bringing
an elephant into class. I took Gregor to a meeting where I was giving a
talk
on critical thinking and a chemist who had just delivered a nice and very
detailed talk said that of course Gregor isn't a dog, he'
is slightly the wrong shape. I responded that biology, unlike chemistry,
isn't a six significant figure science, and general shapes aren't always
reliable (especially for extremely polymorphic species like dogs). Students
aren't the only people who suffer from tunnel vision and/or jump to
conclusions.
Jim Eliason
Manhattan College/College of Mount St. Vincent
Biology Dept.
Hi, labbers:
My favorite analogies aren't nearly as nifty as those of Tom's students
(I
love the splicing one!). But my students seem to find these helpful.
For chromatin vs. chromosomes: chromosomes are skeins of yarn as they come
back from the store (complexly folded and wound into nice, neat bundles);
chromatin is the same bundles after they've been exposed to a two-year old
(or cat). I like this one because, if I tell the students the yarn is
two-ply, I can build on the analogy for other aspects of DNA function.
For energy: at the beginning of the semester, I tell my students that the
fundamental analogy here is simple -- energy = pain. Then, throughout the
semester, I build on that. For example:
For the energy content of different wavelengths of light: imagine each"wave"
of light
has a sledgehammer poised at the peak. Which hurts more, short wavelength
or long
wavelength?
For the potential energy "content" of a concentration gradient:
imagine that the solute
is junk shoved into the closet because your parents are making asurprise
visit. The more
junk, the more pain when you open the door and it all falls on your head.
For the function of electron transport chains in chloroplasts and mitochondria
(for my
classes, the function is just to release energy in small increments): imagine
a bowling
ball perched at the top of a mobile staircase (such as those used at airports).
The
bowling ball has to get to the bottom of the stairs, and can do so two ways
-- over the
"back" of the staircase (straight down) or down the steps. <here,
it gets tricky,
because I ask which way releases more energy -- they all want to say over
the back,
and I need to review potential energy before they all agree that it doesn't
matter>.
Then I ask how *they'd* rather "catch" the bowling ball -- would
they prefer to stand
at the bottom and catch it as it fell off the back, or would they rather
stand one
step below the ball, catch it, move down one step, etc.
For transcription/translation, I use a pretty standard "library"
example --
the nucleus is like a reference library with lots and lots of books, none
of
which can be taken home. That's why we need transcription. I like that
analogy because it lets me talk about how we find, say, a particular
sentence in a book (we find the right volume, the right page, the right
paragraph -- how do our cells do that???? -- we key in on a period, a couple
of spaces, then a capital letter for the beginning of the sentence; our
cells use specific sequences, etc.).
Looking forward to seeing what y'all use :)
Kerry Kilburn
ODU Biological Sciences
I have used an analogy similar to that of Kerry Kilburn. I tell students
that
if they want to know what a nucleus is like they should buy several skeins
of
knitting yarn, unravel it, and stuff it into a plastic bag. Later, when
they
need chromosomes, they send a dwarf with knitting needles into the bag to
knit the skeins into scarves.
Dave Williams
Hi all,
For the transcription-translation scenario I tell the class to
imagine they want to read some famous Russian (or other) novel, but the
only copies in the library are in Russian and in the Russian alphabet.
They have access to a Russian-English dictionary that uses the English-type
alphabet only. The first thing they have to do is to is TRANSCRIBE the
original letters into more familiar English notation. They then can
TRANSLATE the novel using the dictionary. Another variant is to use the
spy trying to decode a message that is in a language other than his/her
own. The first step is to transcribe the coded message into the original
language, and then to translate it into the spy's native tongue.
These analogies have been great. I look forward to incorporating
many of them into future lectures. As someone already commented - seems
like the stranger I make the story the more likely the students will
remember the point I'm making.
Liane Cochran-Stafira
Dept. of Ecology and Evolution
The University of Chicago
1101 East 57th Street
Chicago, Illinois 60637-5415
phone: 312-702-1930
e-mail: lcochran@midway.uchicago.edu
I have had a great deal of trouble introducing students to the concepts
of
hydrophobic interactions in an aqueous environment. What has finally worked
for me is to use a social analogy. Imagine a cocktail party filled with
socially adept people. Each of them forms a series of transient "bonds"
with
others, so that there is a continual ebb and flow of interactions, but in
general, each participant is in contact with others in the group. Now,
into this assemblage walks a "socially challenged" individual.
This person is
unable to interact with others, and wanders around randomly, finally ending
up in the corner reading the magazines. If a second person of this type
enters the room, this one also is shunted around and eventually ends up
in the
same corner, reading a different magazine-but not really interacting with
the
first person. etc.
This indicates not only something about the nature of the water interactions,
but also shows that the hydrophobic molecules are not really bound by anything
intrinsic, but by the common feature of being "rejected" from
interaction
with the others.
This model can be extended even further to include charge intereactions
by
including couples that are strongly attracted to each other, and even
discuss solvation of charges by surrounding each of the members of the couple
with others who are somewhat attracted. You can show how this could lead
to dissolution of the strong bond.
Finally, I can model amphipathic systems by discussing couples in which
one
member is socially adept and the other member inept.
The students seem to tolerate this. It may even be helpful.
Joel B. Sheffield
Biology Department
Temple University
Philadelphia, PA 19122
jbs@sgibio.chem.temple.edu or
v5415e@TEMPLEVM.bitnet
(215) 204 8854
Although I do use some analogies for teaching basic chemistry concepts,
I
have found a nice practical example for students to understand and apply
basic chemical bonding concepts.
Difference between covalent and hydrogen bonding can be effectively
discussed using grooming techniques. Curlers and curling irons through
the addition of heat (energy) change hydrogen bonding patterns in
individual hairs, whereas permanent wave solutions modify covalent bonds
in hairs. This can be used to discuss protein interactions, the
strength of different types of bonding and the application of chemistry
to daily life.
Terry Favero
Biology
University of Portland
I use my favorite analogy when discussing enzymes and their interactions
with substrates. I bring a basketball and a bucket, a golf ball, and my
trusty softball glove and ball to class. Lock and key type interactions
are easily demonstrated with the basketball and bucket, it fits perfectly
into the bucket and kind of sticks inside. The golf ball (wrong
substrate) falls out of the bucket and doesn't make good contact with the
"active site". For induced fit, the softball and glove work great.
Everyone can see how the glove "forms" around the softball to
make it fit
better. The golf ball or basketball doesn't have the same effect on the
glove, and gets a good laugh when a student tosses it to the professor
who then looks kind of silly trying to catch it!
Guy Farish
Biology Department
Adams State College
Alamosa, CO 81102
(719) 589-7969 FAX (719) 589-7242
I too use a ball to simulate enzyme-substrate interaction. However, all
I
use is a soft rubber ball about the size of a softball (with the added
bonus of a built-in squeak). I ask a student to catch the ball
(substrate) with the open palm of one hand held flat (enzyme) -- it's just
about impossible to catch the ball! I then ask the student to catch the
ball as he/she normally would -- the ball is caught when the hand closes
around it -- voila! an induced fit! The added bonus is that the ball
squeaks when caught, indicating that the ball has been squeezed and thus
distorted -- neato! the distortion suggests how chemical bonds in a
substrate may be weakened or stressed by an enzyme, thus lowering the
activation energy required to break the chemical bonds!
Peter Petokas
Department of Biology
Shippensburg University of Pennsylvania
I consider models to be three-dimensional analogies. Eight pinpong balls
glued
together in 2 sets of 4 make a handy model for demonstrating the difference
between spiral and radial cleavage in protostomes and deuterostomes,
respectively.
A sheet of rubber (like a cut balloon) is useful for demonstrating surface
tension of water. If one person stretches it out and another person pushes
her
finger into it, the further she pushes the more the balloon pushes back.
This
is because the balloon, like water, tends to minimize its surface area.
The
surface tension of water in the spongy mesophyll of a leaf provides the
power
for transpiration. Evaporation of water increases the surface area of the
meniscus; the resulting increase in surface tension pulls water out of adjacent
cells. The balloon trick seems to help students with this difficult idea.
Tim Watkins
Univ. Cal. Irvine
twatkins@uci.edu
In the same vein one can liken the plant cell wall to reinforced
concrete. The cellulose fibers are the rods and the lignin and other
amorphous materials form the matrix. It's all laid down differently but
the end result is much the same. Interesting to note that nature got there
first in both cases.
Doug
G. Douglas Crandall, PhD
Biology Department, Emmanuel College
400 The Fenway, Boston, MA 02115
(617) 735-9959
Here are several analogies that I use in general biology.
To describe what happens during crossing over, I bring in a general biology
text that we are not using, and a chemistry book. I ask the students what
would happen if while studying for a test, I took a chapter out of their
text, and replaced it with the same chapter from another text. Someone
usually sees that there will be slight differences between the chapters,
but the general information and hopefully the final product --their grade--
will be similar or the same. However, if I take a chapter from their text,
and replace it with a chapter from a chemistry text. Complete loss of
information, and a change in the final product - their grade.
When discussing the function of enzymes, I ask them to imagine that they
are in a singles bar looking for a date. They can move around until they
bump into someone, and get a date, but that may take a while. If we
increase the numbers of the opposite sex (reactants), there is a better
chance that they will make a connection (product). If we remove all
couples (products) from the bar as soon as they pair up, we increase the
chances of the singles bumping into one another. However, the easiest way
to find a date is to go to have a friend fix them up with someone. This
friend does not get paired up, but is free to fix other freinds until all
the friends get fixed up, or the matchmaker gets tired of matchmaking.
Terry Davin
Biology and Allied Health
Penn Valley Community College
Kansas City MO 64111
davin@kcmetro.cc.mo.us
From: Carol Morris <MORRISC@sunytccc.edu>
To: biolab@hubcap.clemson.edu, petokas@peach.epix.net
Subject: Re: Chemical Bond analogies -Reply
For covalent and ionic bonding, I use a pen to represent electrons.
In ionic bonding, I give the pen to a student; s/he becomes reduced,
I become oxidized. For covalent bonding, we both hold onto the pen;
for polar covalent bonding, we both hold on, but it's closer to one
of us. Simple, easy to do, easy to see, involves the student
audience, and the class usually laughs!
A slinky is a great way to demonstrate the 3D shape of a globular
protein or enzyme. It can have an active site (shove a tennis ball
"substrate" into) and can easily denature. I'm sure everyone already
knows about the tennis balls. I'm afraid I don't know who to give credit
to for this one. Tennis balls (with a big "e-" written on the
side) are
used to represent electrons. They are passed and in pairs from student
to student to represent oxidation and reduction.
Karen McCort
El Paso Community College
I found that I can help students visualize the effects of surface tension
of water by asking them what happens when they push two drops of water
toward each other until they contact. Why don't you get a figure 8? What
will happen if the water is soapy instead? Then I describe placing a
steel needle on water and floating it. They also may be familiar with
tiny depressions in the surface of the water when an insect or other light
object floats on it. They seem to understand these examples without
having to make the transition from an analogy.
Janice
***********************************
Janice M. Glime, Professor
Department of Biological Sciences
Michigan Technological University
Houghton, MI 49931-1295
jmglime@mtu.edu
906-487-2546
FAX 906-487-3167
***********************************
The Super Bowl provided me with a good analogy a couple of years ago. I
use it
when describing the maintenance of central arterial blood pressure in order
to
adjust flow to one organ bed without siultaneously affecting flow to another
organ bed. Municipal water systems are designed on the same principle: by
maintaining a central pressure, the water department can guarantee that
you can
water out of your tap even when your neighbors turn on theirs. The ability
to
regulate that central pressure has been exceeded: The Los Angeles Dept.
of Water
and Power put out a general request that people not flush their toilets
during
every Super Bowl commercial break. Apparently in the past, the sudden demand
to
refill toilets in millions of homes was sufficient to cause a substantial
pressure drop in the lines supplying water to fire hydrants, hospitals,
etc.
Tim Watkins
UC Irvine
To get my students to remember surface tension, I tell them about the
experiment I did as a kid, with a tiny bug on the surface of water in a
bowl. How does it not sink? Then you dip a toothpick in soap, touch it
to the water, and the bug drowns!! Sick, eh? But they remember
surface tension!!
Also, to get them to remember mRNA structure, I come to class with
a baseball cap with an upside-down G on it, and I made a tail out of an
old belt that I covered with "AAAAA" stickers. I look incredibly
stupid,
but believe it or not, that's the one question the students always get
right on their comprehensive exams, 3 years after that class!
-Bob Moss
Wofford College
MOSSRE@WOFFORD.EDU
Bob Moss wrote:
"To get my students to remember surface tension, I tell them about
the
experiment I did as a kid, with a tiny bug on the surface of water in a
bowl. How does it not sink? Then you dip a toothpick in soap, touch it
to the water, and the bug drowns!! Sick, eh? But they remember
surface tension!!"
One portion of a several-day lab regarding surface tension, diffusion, and
emulsion is to have students pour milk (whole milk, not nonfat) into a
shallow glass bowl; finger bowls are great, watch glass is too small.
After it sits for a minute so that it is mostly "still" with no
currents,
have each group *carefully* drop one drop of each of 2 or 3 or 4 colors
of
food coloring in various places around the surface. It only takes one drop
of each. They observe for a minute, seeing only slow mixing; much slower
than what they previously observed when doing the same experiment with
water. Then they touch the tip of a toothpick into a liquid dishwashing
soap, get a good-sized drop of it on the end of the toothpick, and gently
touch the surface of the milk. The results are truly astonishing, and can
keep anyone fascinated for several minutes as the milkfat emulsifies and
the food colors swirl in psychedelic kaleidoscopic patterns. This is also
just plain fun with a small child, or with anyone who is still a little
curious kid at heart.
JodyLee
JodyLee Estrada Duek jduek@u.arizona.edu
Faculty Development Specialist 520/626-2203
Division of Academic Resources 520/626-6707
U. of Arizona School of Medicine 520/626-4879 (fax)
1501 N. Campbell Avenue
Tucson, Arizona 85724-5120
Hi folks,
I have really enjoyed some of the analogies presented here, so I will
throw in one of mine.
Fluidity of Membranes: Any of your out there with young children have
undoubtedly been introduced to the "ball rooms" at MacDonalds.
I use
this to describe how proteins can move through biological membranes. I
liken the balls to phopholipids and my son to an integral protein. When
my son is in the ball room, he never stays in one place, rather he moves
around, and the balls give way to him. Nonetheless, the integrity of the
ball room itself is not compromised by his movement. Okay, I know that
the balls don't form a bilayer, but they get the idea!!
Fun with Ballons: It is amazing what you can do with those long balloons
that clowns use for making animals etc. I often use a few of these to
demonstrate the interactions of chromosomes during mitosis and meiosis.
You can make homologs, show how chiasma form by winding two balloons
together (although you never can finish the crossing over mechanism
without busting your balloons!!). The bonus is if a balloon pops---it
wakes everybody up!!
Dr. Kevin Piers
Box 5005
Red Deer, Alberta T4N 5H5
Canada
Here's one I like to use. Coevolution: the highway patrol and speeders.
The patrolmen got radar. The speeders got radar detectors. The patrolmen
got a new band. The speeders spent more on their detectors. The patrolmen
got instant on. The speeders got jammers. For some reason the students on
a campus that is 50% commuters can relate to this.
Also. I learned this one from Roger Thibault here at BGSU. To explain
sister chromatids, homologous chromosomes, genes, alleles and crossing over
I bring in two sets of newspapers. Two copies of today's BGNEWS are sister
chromatids. A copy of today's BGNEWS and a copy of yesterday's BGNEWS are
homologous chromosomes. The sports section represents a gene. Today's
sports news about the hockey win is one allele. Yesterdays news about the
hockey loss is a different allele. Same gene --sports different allele --
win versus lose. Crossing over happens when you mix up the two papers and
yesterday's sports section gets mixed into today's paper. Roger has made
some simple plexiglass rings to represent the centromeres.
Let's keep this thread going. I've gotten a lot of great ideas. Thanks.
--cmw
Charlene M. Waggoner, Ph.D. "Great art is eternal;
Department of Biological Sciences great science tends to be
Bowling Green, State University replaced by greater science."
Bowling Green, OH 43403
-- John A. Moore
cwaggon@bgnet.bgsu.edu
Charlene,
Thanks a million for the newspaper analogy. My students had a terrible
time understanding the difference between chromosomes and chromatids and
how a chromatid could become a chromosome. I finally resorted to using an
analogy of a room with 10 pregnant women. If we count them, we only count
10 people, but the baby is already formed. Later, if we go into the room
and all 10 have had their babies and are holding them, we count 20 people,
but the babies have not really changed, only separated from the mothers.
The parallel is not so good, but it seemed to have helped my students see
how a 2 chromatids could be counted as one chromosome, then later be
counted as two chromosomes just because they separated.
Janice
***********************************
Janice M. Glime, Professor
Department of Biological Sciences
Michigan Technological University
Houghton, MI 49931-1295
jmglime@mtu.edu
For demonstrating how maternal and paternal chromosomes can segregate
during meiosis (sans crossing-over), I use two "decks" of common
Bicycle
playing cards. Each "deck" consists of the 13 cards of a single
suit (eg. A
thru K of hearts), and represents a complete set (N) of chromosomes. One
deck has a red back (the maternal chromosomes) and the other has the dark
blue back (the paternal chromosomes).
The students can see that each parent is contributing a complete set of
13
cards (chromosomes) to the zygote which will have 26 chromosomes after
fusion of the two decks or gametes. Now mitosis eventually produces the
2N
cell that is destined to undergo meiosis in the sexually mature parent.
The
cards and mixed around face up.
I a student to pick a complete set of cards (chromosomes) from the pile.
They realize that meiosis is not just halving the 26 to 13, but meiosis
guarantees gametes with complete sets. After they have created their own
complete set, they turn the cards over and see that some of the chromosomes
in their new gamete were originally maternal (red) and some paternal
(blue). We then figure what the chances are of this imaginary critter (with
N = 13) coming up with a sperm just like the sperm that made it. Without
even considering crossing-over, it is 2 to the 13th. We then figure out
the
probability of a guy in the class making a sperm just like the sperm that
dear old dad used to make him (again, no crossing over).
ED BURLING
DeAnza College
E-mail: eb04124@tiptoe.fhda.edu
Tel: (408) 864-8625
Cupertino, CA 94014
An idea that works for my students when we discuss the behavior of
chromosomes during mitosis and meiosis is shoes. We all know that
shoes come in recognizable pairs (homologous chromosomes) which are
identifiable as members of a particular pair (red dress shoes, for
example), altho they are not identical (left vs. right: each homolog
may carry different alleles). During interphase, the "shoes" are
in a
jumbled pile. During prophase of mitosis, they sort themselves out in
the closet; during prophase I they find their mates and pair up.
If only my closet worked those chromosomes do!
Carol Morris
Tompkins cortland community College
Dryden NY 13053
607.844.8211 ext 4425
morrisc@sunytccc.edu
On Mon, 6 May 1996 Jim Ingold wrote:
> My favorite analogies:
>
> 1. most connective tissues i.e. cartilage:
>
> are like Jell-O (non-cellular matrix) with fruit cocktail (cells)
> mixed in it
I've used Jim's fruit jello analogy for connective tissue, but I like
using REINFORCED CONCRETE better. It's HARD (like bone), it contains
GRAVEL (like bone cells), it contains REINFORCING RODS (like fibrous
proteins), and it's all bound together with CEMENT & SAND (the matrix
of
bone).
Peter Petokas