BIOTECH Project University of Arizona
Reproducing a Cootie and the Inheritance of Traits
Introduction:
Cooties are an unusual life form that have lived on opposite sides of the Sierra Madre Mountain range in
Mexico, and have not reproduced with each other for thousands of generations. The Cooties from the two
regions in the mountain range look very different. Cooties from the east side of the mountains where the
rocks are mostly red sandstones have red bodies. The Cooties from the west side where bluish rocks are
found to have blue bodies. We assume that these color differences help them survive in their different
environments.
We have observed a total 5 physical characteristics, traits, between the two groups of Cooties:
1. Body and head color that is either red or blue
2. Ears that are either wide ear or bow
3. Eyes that are either plain eyes or lashes on eyes
4. Mouths that are either lips or tongues
5. Feet that are either boots or feet
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
Cooties from the east side of the Sierras always have the following 5 traits: red body color, wide
ears, plain eyes, lips and boots. Because they always have these traits, these Cooties are “true
breeding” for these traits.
Cooties from the west side of the Sierras consistently have the other 5 traits: blue body color,
bows, lashes on eyes, tongue and feet. These Cooties are “true breeding” for these traits.
Recently researchers tried to mate the Cooties from the two different regions and found that they were
still able to reproduce. You will investigate what happens to the Cooties offspring’s five traits when they
are mated. A program has been written to help us visualize what the offspring will look like depending
on which cooties are used in the mating.
1. If a Cootie that is true breeding for red body color, wide-ear, plain eyes, lips and boots were to
mate with a Cootie that is true breeding for red body color, wide-ear, plain eyes, lips and boots,
what would you predict their babies would look like?
2. If a Cootie that is true breeding for blue body color, bow ears, lashes on eyes, tongue and feet were
to mate with a Cootie that is true breeding for blue body color, bow ears, lashes on eyes, tongue
and feet, what would you predict their babies would look like?
3. What if a Cootie that is true breeding for red body color, wide-ear, plain eyes, lips, and boots were
to mate with a Cootie that is true breeding for blue body color, bow ears, lashes on eyes, tongue
and feet, what do their babies look like?
4. What happened and why do you think this happened? Come up with a hypothesis as to why you
got these results and what could you do to test your hypothesis?
We will now take two of the above Cooties and mate them. Remember one of their parents had visible
traits of red body color, wide-ear, plain eyes, lips, and boots; the other parent had visible traits of blue
body color, bow ears, lashes on eyes, tongue and feet. We lost some of these traits in this generation,
what do you think will happen in the next generation if we mate two of these cooties?
(c) 2009-2010 The Arizona Board of Regents on Behalf of The University of Arizona
BIOTECH Project University of Arizona
To play the Cootie Genetics game, break up into groups of three:
 One of you will be the mother
 One of you will be the father
 The third person will record the offspring reproduction events (the doctor)
You will make 40 offspring, recording the five different traits by random selection of the ”trait factors” by
two individuals (the parents). Record factors in the computer program as was demonstrated in the
reproduction and offspring generation yesterday.
We will abbreviate the factors for trait that we see with the capital letter referring to the trait visible in this
generation, and the small letter referring to the trait we do not see if this generation. For the factors that
represent the five traits the one letter abbreviation that we will use are as follows:
Red body color (R) blue body color (r)
Wide-ear (W)
bow (w)
Plain eye (P)
lashes on eyes (p)
Lips (L)
tongue (l)
Boots (B)
feet (b)
The one-letter trait corresponds to one of the colors of the cubes, which you are going to use as the factor
that will determine the traits of your offspring. You will be randomly selecting for each of your
offspring’s traits Body color trait factors: R=red, r=blue; Ear trait factors: W=white, w=black; Eye
trait factors: P= purple, y=yellow; Mouth trait factors: L=Light green, l= orange; Feet trait factors
B=Brown, b=green.
To make the offspring you need to find out what traits it will have. It turns out that both parents start out
with factors for both red and blue body color, they should have the ability to give either of these factors to
their offspring. As a parent you have a cup with either a red or blue factor, you will randomly pick the
factor from the cup to give to your offspring. After the doctor has recorded each parents’ trait factors,
return the cubes to the cup. This way there is always a 50% chance for each of the trait factors.
To make the first offspring each parent will:
 Reach into cup 1 and pull out the factor for body color (either a red or a blue cube).
 The “doctor” will record which body color factors the offspring received from the parents. Be
careful to record which factor (cube) is from mom and which is from dad.
 Reach into cup 2 and pull out the factor for auditory appendage (either a white or a black cube).
 The “doctor” will record the auditory appendage factors the offspring received from the parents.
 Reach into cup 3 and pull out the factor for ocular appendage (either a purple or a yellow cube).
 The “doctor” will record which ocular appendage factors the offspring received from the parents.
 Reach into cup 4 and pull out the factor for vocal appendage (either a light green or an orange
cube).
 The “doctor” will record which vocal appendage factors the offspring received from the parents.
 Reach into cup 5 and pull out the factor for motile appendage (either a brown or a green cube).
 The “doctor” will record which motile appendage factors the offspring received from the parents.
Once the first offspring is completed, check out your baby, what traits does it have? Same as Mom and
Dad? Different? Any of the grandparent’s traits show up? Do the same thing to make the second
offspring, then the third and so on. The key is to keep it random, so don’t look in the cup and try to get a
specific color cube.
(c) 2009-2010 The Arizona Board of Regents on Behalf of The University of Arizona
BIOTECH Project University of Arizona
Analysis of Cootie Genetics
Let’s review what we have learned about the inheritance of traits by Cooties:
Recall the original Cooties were either true breeding for red body, wide-ear, plain eyes, lips and boots or
true breeding for blue body, bow, lashes on eyes, tongue and feet
True breeding means that if two Cooties with red body, wide-ear, plain eyes, lips and boots mate, they
will only have babies with red body, wide-ear, plain eyes, lips and boots. If two Cooties with blue body,
bow, lashes on eyes, tongue and feet mate, they will only have babies with blue body, bow, lashes on
eyes, tongue and feet.
We discovered that a Cootie with red body, wide-ear, plain eyes, lips and boots mates with a Cootie
Cooties with blue body, bow, lashes on eyes, tongue and feet, all of the offspring look like this:
Red body, Wide-eared, Plain eyes, with Lips and Boots. These babies looked just like mom and had
nothing of dad….What happened to Dad’s traits?
We then took two of those Cooties and mated them to see what the offspring looked like:
1. How many different Cooties did you have (look at the traits)?
2. How many Cooties had traits that you did not see in the parents?
3.
How many of your Cooties had the same factors as the parents (look at the factors recorded by the
doctor) how many Cooties had factors that were different from the parents?
4. Did the Grandfather’s traits reemerge?
Using the data you recorded in the Cootie offspring file to fill in the following:
Total # of
RR
Total # of
Rr
Total # of
rR
Total # of
rr
Total # of
Red
Total # of
blue
WW
Ww
wW
ww
Wide-ear
bow
PP
Pp
pP
pp
Plain eyes
lashes on eyes
LL
Ll
lL
ll
Lips
tongue
BB
Bb
bB
bb
Boots
feet
Recall the factors correspond to the following cubes: R=Red & r=blue, W=White& w=black, P=Purple &
p=yellow, L=Light green & l=orange, and B=Brown & b=green.
(c) 2009-2010 The Arizona Board of Regents on Behalf of The University of Arizona
BIOTECH Project University of Arizona
Look at each trait individually and determine the percentage of Cooties for each trait:
1. How many red Cooties were there compared to blue, compared to total number of Cooties; how
many of your Cooties had wide-ears and how may bows, etc?
2. Do you see a trend? Does one trait appear more often than the other? If yes, why do you think
this is the case?
3. Are both grandparents’ traits represented in the Cootie offspring of your reproductions? If yes, are
they represented equally? Why do you think you had the number of offspring with each
represented trait (Red versus blue, plain eyes versus lashes, wide ear versus bow, etc)
We know what factors were involved in the representation of each of the traits for all of your Cootie
offspring. Each parent had two possible factors that they could offer each of their offspring, however they
could only give them one. For example both mom and dad have the R trait factor (for the red cube) and
the r trait factor (for the blue cube), however each can only give one of these trait factors to their child.
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What are the four possible trait factor representations that Mom and Dad could give their child for
body color (represent Mom first)?
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From your data, at what ratio are the four possible factor combinations represented in your Cootie
offspring?
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What can you say about this ratio?
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How do the ratios for the trait factor combinations compare to the ratio for your traits?
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What conclusions can you make from your data?
(c) 2009-2010 The Arizona Board of Regents on Behalf of The University of Arizona