Lesson I: Genotype and Phenotype
Key Concepts:
Genotype/Phenotype
Dominant/ Recessive
Environment vs. Inheritance
Materials Needed:
Q-tips
Blue food coloring
PTC paper
Flashlights
Hand mirrors
Small cup for food coloring
Dissection Microscopes
Nematodes
Drosophila
Jelly Beans (can purchase from Jelly Belly Candy Co.)
Introduction
Start by introducing yourself and statement in a sentence or two what you work on and why it matters.
Use language that is appropriate for 7th grade. Have all volunteers do the same. Inform students that for this
class there is a 10 minute group discussion and then students will be divided into 3 groups and will go to a
workstation. We will rotate so that everyone spends time at each workstation.
Today’s class will begin with the discussion of how we acquire our characteristics or traits. Traits are
determined by (i) our genes, (ii) the environment or (iii) from a combination of our genes and our environment.
Ask students if they have heard of genes (not the pants). Where do we get our genes? Remind students
that we receive one copy of each gene from each of our parents, therefore, we have two copies of every gene.
Genes carry information that determines our inherited characteristics.
Start by discussing the inheritance of simple traits, those that are determined by single genes. Examples
of simple traits include: the ability to roll one's tongue, having attached earlobes, and the ability to bend ones
thumb back (hitchhiker's thumb)(see appendix, page 18). Ask students "Who can role your tongue?" Count
rollers vs non-rollers. Write numbers on the board If time, can do the same for other traits.
One of the simplest traits to examine is the ability to roll one’s tongue. It is believed that the ability to
roll one's tongue is due to the presence of a certain muscle in the tongue. If you have that muscle, you will be
able to roll your tongue. Give the example of the form of the gene symbolized by "R" that has the information
required to make the specific muscle in the tongue that allows us to roll the tongue. The form of the gene that
does not have the information is called “r”. If a person has one or two copies of the "big R" gene then he/she
will be able to roll their tongue.(write on board: genotype RR and Rr. Ask can they role their tongue?). If
he/she does not have this gene and instead has only two copies of the recessive "little r" gene (rr) then he/she
will not have the ability to roll their tongue. The big R form of the gene is said to be dominant to the little r
form because individuals who are Rr do make the muscle and can roll their tongue. Write on the board
RR, Rr, rR, rr and go over concept of genotype vs. phenotype.
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Ask: Are there any traits determined purely by environment? (may say painted nails or dyed hair)
[Hair color is determined by at least four genes, each one coding for the production of melanin, a brown
pigment. Because the effect of these genes is additive, hair color can range from blond (little melanin) to very
dark brown (much melanin). Hair color can also be just determined by our environment-ask the children why?
[from dying the hair]
Many traits result from a combination of our genes and the environment. Ask students for possible examples.
One example is height. Why might genes be important? (parents and children tend to be similar)
Ask the students, “What environmental factors could influence our height? Why are people generally taller than
they were 200 years ago? Ever visited a home built 200 years ago? The ceilings are generally lower than they
are today” Bring up issue of diet if students haven't mentioned it.
Height is determined primarily by our genes (80%) but are strongly influenced by the environment.
Activity: Ask for volunteers to come to the front of the room, choose one boy and one girl, and give them each a
coin with the allelic forms R and r written on each side (or one coin with only r on each side) representing a
hypothetical genotype for each parent.
Say: “Let’s pretend that this is a father and this is a mother and they are planning on having children”. They
each have two forms of the tongue rolling gene that they can pass on to their child. I am going to have them flip
the coin to determine which form they pass to their child. The students should flip the coins and the results of
each toss should be written on the board; the rest of the class is asked if the child can roll its tongue or not. Point
out that each time there is a 50:50 probability of passing one of your two genes. The same chance for each
child.
If time, set up a Punnet square on the board as being useful in determining what different genotypes children
could inherit based on the genotypes of their parents. We can also estimate frequency.
Workstations:
Divide children into three groups, they will spend about 10 minutes at each workstation.
1.
Nematodes

Dissection Microscopes should be set up for the students to look at wild-type worms before class starts
(adjust course and fine focus). Light should be on high setting and clear discs covering light source.
Show students how to adjust eye piece on microscopes.. Explain microscopes and adjusting the eye
piece. Students can put their finger on the clear disc and see how it looks magnified
a. Hold up a dish and ask if students can see anything. Explain that we will be looking at special worms
called nematodes. They are present in the soil when you pick up dirt but they are so small cannot be
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seen. With microscopes we can see the worms. They help fertilize the soil by eating bacteria produced
from dying plants and animals and excreting the waste products back into the soil. Key Point: Many
organisms are too small for us to see with our eyes. In the case of nematodes present in soil.

Ask students to look at dishes-what do you see? Do they notice any body parts.

Then compare phenotypes of worms in different plates (could be dumpy, roller, etc). Discuss worms
(see points below)
For your information if they ask: Each dish has agar on bottom with bacteria spread on top (circle). A piece of
agar from another plate with worms is put on new plate. The worms migrate towards the food.
Points for Discussion on Worms:
b. Nematodes are present in the soil but we can’t see them with the naked eye. They are so abundant that
the only place on earth one can pick up a handful of soil without a nematode is in Antarctica.
c. They help fertilize the soil by eating bacteria produced from dying plants and animals and
excreting the waste products back into the soil.
d. Nematodes are either males or hermaphrodites meaning that one animal has both female and male parts;
because the nematode can self-fertilize, it's offspring are genetically identical to itself.
Disadvantage of being a hermaphrodite vs. having a mother and father. Lack diversity
Advantage-don’t need to find a mate.
e. There are many different kinds of Nematodes, many of which are benign but some are
parasitic such as the ringworm, heartworm, and tapeworm.
Note: Some of the students may have a fear of worms. Explain that the worms are under the plastic lid and that
it is safe to touch the dish.
2.
Drosophila
Supplies: Drosophila life cycle cards, magnifying glasses, flies
Questions: Start by asking students if they have heard of fruit flies.
Ask the students why we call them fruit flies. When have they seen fruit flies before? (around rotting fruit)
The technical name for the fruit fly is Drosophila (word is written on the life cycle cards). The flies eat the fruit
or the mold on the fruit and lay their eggs in it.
Before passing out flies, hold up picture of fly life cycle. Observe different stages of life cycle: egg-larvaepupae adult. Introduce and define word “METAMORPHOSIS” and ask students to repeat. Ask students about
other insects that have similar life cycles? (e.g. butterflies/moths). The complete cycle for the fruit fly is 10
days. Key Point: different stages of insect development and concept of metamorphosis
Hold up vial. Explain that food is on the bottom (molasses, cornmeal and yeast).
Ask the students what they see in the vials. There are adult flies, but there are also larvae in the food and on
the walls and pupae on the walls. (The eggs are too small to see). Egg hatches, larvae eat for a week. Then
climbs up onto the wall of the vial. It finds a good spot, then secretes a hard shell and enters the pupal stage.
During this stage the fly metamorphoses from the larva into the adult.
Fruit flies have easily visible phenotypes. What color are their eyes? What shape are their wings? Wild-type
flies have red eyes and straight wings. Their bodies are a cream color with black strips on the back. Now ask
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the students to compare the flies with a different phenotype (curly wings, white eyes, ebony body, etc.). What
is different?
If there is time, here are some Drosophila facts:


The females are larger than the males. Males have a dark tip at the base of their abdomens. Can the
students spot the difference? Make point that male is not always bigger in different species
Fruit flies can survive for weeks without food. They can only survive for a few days if they don’t have
enough moisture (water), similar to humans.
Turn vial upside down and watch what happens.
3. Heritable Traits and Taste Buds
(Place this workstation as close to a sink as possible)
Question: How do we taste things (ask students)?
Five tastes: sour, bitter, sweet, salty and unami ( savory, detects flavor enhancer monosodium glutamate)
Show card with picture of tongue and different tastes.
Question: Is smell involved in our ability to taste?
Tongue Activity
Start by asking, "Does everyone taste food the same way"? How do you know that? Key Point: There
are genetic differences in how we taste some things. We have a piece of paper with a chemical substance on
it (phenylthiocarbamide (PTC). We will hand out the paper and when you put it on your tongue you will either
taste something or not. Because the paper will taste bitter to some people, you can rinse your mouth at the sink
if necessary. Tell the children that participation is optional.
 Hand out the taster paper but have the students wait until everyone has a piece before putting on
their tongues. Tell them we will all put the paper on the tip of your tongue on the count of 3. Count 1,2,3.
Watch the reactions. Most will taste the PTC paper but there will be some students who do not. Make the
other students aware of the student who can taste and who cannot. Tasters can rinse their mouth if needed.
 Turns out that a structure on the tongue containing taste buds is called a fungiform papillae.
Have students say Fungiform papillae. In adults, people who taste less, have larger and fewer papillae
whereas strong tasters have many small papillae. (Phenylthiocarbamide (PTC) tastes bitter to about 7 out of
10 adults but less is known about children).
 Explain to students that we can observe their fungiform papillae by placing blue food coloring on
the tongue. Papillae don't absorb food coloring so they look pink on a blue background. Let’s see what the
tastebuds look like on the tasters and non-tasters.? (again options).
 Start with one taster and one non-taster so students can see if the papillae are different.
 Have ready a small bowl with blue food coloring, Q-tips, flashlights and mirrors. Take a clean
Q-tip and absorb a small amount of the food coloring. Roll it on the end of the students' tongue. Shine a
light on the tongue to see the papillae. Give children a flashlight and mirror to see for themselves. Make
sure you are the only one putting on the food coloring. Allow students to rinse their mouth if they would
like. Food coloring is not harmful if swallowed. Inform students it will be gone by the end of the day
Smell activity
Ask “Is there anything else besides the taste buds on our tongue that affect our ability to taste
things? “ Don’t give the answer. Do the experiment first and then ask question again.
1. Give children a few jelly beans and have then hold their nose
2. Put jelly beans in their mouth and begin to chew (I use jelly bellys-not all kinds work well)
3. Release nose. Do they now taste flavors that they could not before
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(Note: if chew for a long time will start to taste flavors as molecules can enter nose either directly from
the air or through the mouth.). Key Point: Smell affects are ability to taste.
Note: some children do not want to participate—that is just fine. No one should feel pressured to participate.
Also, try to have a non-taster run the taste bud station. The students are rather reluctant to taste the
PROP strips if the leader does not taste it with them
Points for Discussion:
(i) We have hundreds of receptors for smell (about 400). The combination of receptors that are activated
determine what we sense.
(ii) Ask: What happens when we have a cold and our nose is stuffed up. Do we taste food as well?
With age our ability to smell decreases and we don’t taste as well.
(iii) What might be the advantages and disadvantages of people tasting differently.
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