Download Parental Alleles and Phenotypes

Lesson Plan
Unit: Mendelian Genetics
Position within Unit: Summary
Title: Purple People eater (by Jennifer Kloock)
OBJECTIVES(S)
PURPOSE
This lesson will help the students to review and crystallize knowledge of Mendelian
Genetics and give them an opportunity to demonstrate their mastery of the material. It also
gives them practice with Punnett Squares, calculating genotypic and phenotypic ratios, and
can be used to review the basics of meiosis.
CA STANDARDS
2. Mutation and sexual reproduction lead to genetic variation in a population. As a
basis for understanding this concept:
a. Students know meiosis is an early step in sexual reproduction in which the
pairs of chromosomes separate and segregate randomly during cell division to
produce gametes containing one chromosome of each type.
b. Students know only certain cells in a multicellular organism undergo meiosis.
c. Students know how random chromosome segregation explains the probability
that a particular allele will be in a gamete.
d. Students know new combinations of alleles may be generated in a zygote
through the fusion of male and female gametes (fertilization).
e. Students know why approximately half of an individual’s DNA sequence
comes from each parent.
f. Students know the role of chromosomes in determining an individual’s sex.
g. Students know how to predict possible combinations of alleles in a zygote
from the genetic makeup of the parents.
3. A multicellular organism develops from a single zygote, and its phenotype
depends on its genotype, which is established at fertilization. As a basis for
understanding this concept:
a. Students know how to predict the probable outcome of phenotypes in a genetic
cross from the genotypes of the parents and mode of inheritance (autosomal or
X-linked, dominant or recessive).
b. Students know the genetic basis for Mendel’s laws of segregation and
independent assortment.
MATERIALS
Purple people eater Genetic charts (below) with examples of proper pipe-cleaner segments
glued into appropriate boxes
Pipe Cleaners in enough different colors to supply at least two alleles for each trait (more if
multiple alleles are desired).
Worksheet (below) to use as a guide to the activity.
ACTIVITIES
Introduction
(Anticipatory Set)
(2 Minutes?)
Today we will use what we've learned about genetics to see how variation can be generated
by the processes of meiosis and fertilization: or, if you prefer, sex. To do this, we will look
at an interesting and rare organism, the flying purple people eater (show picture of Flying
purple people eater; there are many available on the web; here's one of them :http://www.soundry.com/images/PPE-Alone-On-Black.gif. If you can get – and stomach –
the song, you may consider playing it as well).
[Activity #1 Review
and terminology]
(5 minutes)
Spend a few minutes going over the possible variations in the flying purple people
eaters genetic traits (See Chart) and show students how to read the chart: Each group
should get one chart to refer to. Be sure to review the terminology on the chart, and for
each trait, ask students which phenotype would be present for some combination of alleles.
Review the terms genotype (genos=descent, type=form; therefore the inherited form)
and phenotype (phenos=to show, therefore the form that shows, or is visible)
[Activity #2 Purple
people Eaters]
(40 minutes)
Worksheet. It is pretty self explanatory. Have students go through the worksheet in pairs
to develop 10 offspring from the same mating. Each student can have a different genotype,
but make sure that they have a mix of homozygous dominant genotypes, homozygous
recessive genotypes, and heterozygous genotypes so that they will see a variety of patterns.
You do not want any individuals that are homozygous for all traits (too boring!).
Remember that this lesson is designed as a summary activity – if you try to use this to
teach the basics of Punnett squares, you will lose the students. This assumes a basic level
of acquaintance with the concepts.
At first glance, the worksheet can look overwhelming, but it is very repetitive. After the
first few iterations, students can start to see the basic pattern, and this helps them cement
the concept.
Conclusion: Timing
depends on choice
of homework or
classwork
Assign the write-up, either as homework or to do in another class period. Drawing the
purple people eaters is actually a key part of the activity: Students need this step to
visualize the variation produced by sexual reproduction. This also gives your students with
artistic ability a chance to stand out in class as they draw the creatures and turn the dry,
boring phenotype descriptions into a "living" product. – let them show off their drawings.
ASSESSMENT
See attached instructions for the write-up.
REFLECTION
Simplify or Add complexity:
This lesson can be simplified or have complexity added in a variety of ways as needed for
the level of your class.
In the example here, there is one trait that has multiple alleles, and another that
shows incomplete dominance. These traits can be removed to simplify the exercise, or
more can be added to make it more difficult.
The total number of traits can also be reduced, but I don't recommend going below
about 5 traits. Having more traits increases the diversity in the offspring, and if you
remove too many traits, you will lose this important aspect of the lesson.
By adding a stripe on some of the sex chromosomes, you can introduce a sex
linked trait (X or Y-linked). Linked traits on somatic cells can also be added via this
method.
Adjust the number of traits and the complexity to fit your class and time period.
They can easily do all the crosses given here in a single class period, but may need
more time to construct all of the Punnett squares and calculate frequencies: Can be
done as homework, or in another class period. My thanks to Jennifer Kloock (Biology
teacher, Garces High School), for allowing me to use this lesson.
One-Eyed, One-Horned, Flying Purple People Eaters
Chart 1: PURPLE PEOPLE EATER CODE EXPLANATIONS
TRAIT
DOMINANT ALLELE
RECESSIVE ALLELE
Yellow Eyes*
Red Eyes*
Dark Purple Fur
Pale Purple (Lavender) Fur
Eye Color*
Fur Color
Horn Color*
Orange Horn
Pink Horn
Red Horn
Fur Pattern
Striped Fur
Spotted Fur
Dark Blue Wings
Pale Blue Wings
Rounded Wings
Pointed Wings
Ringed Horn
Solid Horn
Pointed Ears
Rounded Ears
Male
Female
Wing Color
Wing
Shape
Horn
Pattern
Ear Shape
Gender
* Be Careful!!!!
Incomplete dominance
Eye color: red chromosomes
Brick (Y) codes for yellow eyes.
Red (y) codes for red eyes.
Multiple alleles
Horn color: orange chromosomes
Dark orange (H’) codes for orange horn
Bright orange (H) codes for a pink horn
Light orange (h) codes for a red horn
H’ is dominant to H and h. H is dominant to h.
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Each of us consists of a unique mixture of traits from our parents. Only identical
twins share a DNA code. (Even identical twins have minor differences due to mutation.)
All organisms that reproduce sexually have this in common. Here we are only going to
deal with 9 traits. As you do this and see how different the outcomes can be, imagine
how many different people just your parents could code for with their thousands of traits.
Never again will your genetic code be exactly reproduced. You are a unique individual.
When we look at only one trait at a time there can be many offspring with that particular
trait. It is when we look at a combination of traits that things start to get interesting.
You and your lab partner have each been given a set of chromosomes. You will use only these
chromosomes when you reproduce. You each should have two of each of the following colors (you may
have different shades of these colors: the different shades represent different alleles):
Blue
Purple
Green
Orange
Pink
Red
Yellow
Brown
Additionally you will need to have either two white or one white and one black. Black
represents the Y-chromosome and white represents the X chromosome; together, these
determine the gender of your purple people eater.
1. With your lab partner decide who is to be parent A and who is to be parent B.
2. Parent A is not to alter the shape of their chromosomes. Parent B is to bend each of
their chromosomes into a spring. This step helps ensure that you each get back your
own chromosomes after each mating.
3. Record both your and your partner’s genotypes and phenotypes as appropriate. Use
Chart 1 to determine your phenotype.
4. Each of you needs to separate your chromosomes into color pairs.
5. Close your eyes and select one of that pair. DO NOT LOOK. This is the random
assortment that occurs during meiosis.
6. Place the one that you have selected with the one your partner has selected in the
same way.
7. Continue to do this, one trait at a time, for each of the 8 traits. This new combination
of chromosomes is your first offspring.
8. Record the results as appropriate. Use Chart 1 as needed.
9. Separate your chromosomes from your partners. so that you have your original
genotype.
10. Continue doing steps 4 – 9 until you have produced 10 offspring.
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Parental Alleles and Phenotypes
Trait
Parent A
Parent B
Allele A Allele B Phenotype Allele A Allele B Phenotype
Eye color
Fur color
Horn color
Fur pattern
Wing color
Wing shape
Horn pattern
Ear shape
Gender
Offspring Genotypes
Offspring
number
Contributing
parent
A
Eye
color
Fur
color
Horn
color
Fur
pattern
Wing
color
Wing
shape
Horn
pattern
Ear
shape
Gender
1.
B
A
2.
B
A
3.
B
A
4.
B
A
5.
B
A
6.
B
A
7.
B
A
8.
B
A
9.
B
A
10.
B
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Offspring Phenotypes
Offsprin
g
number
1.
Eye
color
Fur color
Horn
color
Fur
pattern
Wing
color
Wing
shape
Horn
pattern
Ear shape
2.
3.
4.
5.
6.
7.
8.
9.
10.
Single-trait Punnett Squares:
Eye Color
Fur Color
Horn Color
Parent A
P
a
r
e
n
t
Parent A
P
a
r
e
n
t
Parent A
P
a
r
e
n
t
B
B
B
Fur Pattern
Wing Color
Wing Shape
Parent A
P
a
r
e
n
t
Parent A
P
a
r
e
n
t
Parent A
P
a
r
e
n
t
B
B
B
Horn Pattern
Ear Shape
Gender
Parent A
P
a
r
e
n
t
Parent A
P
a
r
e
n
t
Parent A
P
a
r
e
n
t
B
B
B
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Gender
Single-trait Statistics:
Phenotype
Expected
fraction
Actual
fraction
Expected
percentage
Actual
percentage
Yellow eyes *
/4
/10
%
%
Purple fur
/4
/10
%
%
Orange horn *
/4
/10
%
%
Striped fur
/4
/10
%
%
Dark blue
wings
Rounded
wings
Ringed horn
/4
/10
%
%
/4
/10
%
%
/4
/10
%
%
Pointed ears
/4
/10
%
%
Male
/4
/10
%
%
* Be sure to pay very close attention here!!
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Double-trait Punnett Squares:
Fur Pattern and Fur Color
Wing Color and Wing Shape
Parent A
Parent A
P
a
r
e
n
t
P
a
r
e
n
t
B
B
Eye Color and Horn Color
Ear Shape and Gender
Parent A
Parent A
P
a
r
e
n
t
P
a
r
e
n
t
B
B
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Write-up:
1. Draw a portrait of yourself and your mate. Be sure to use the traits that you are given.
2. Draw portraits of at least three of your offspring. Try to show as many different outcomes as
possible when you select the ones you want to do.
3. Fill in the statistical information above.
4. Fill in the Punnett squares above.
5. Address the following questions:
What are alleles?
What are phenotypes?
Do your children look exactly like you or your mate?
Why or why not?
Do all of your children look exactly like each other?
Why or why not?
Do all of your children have similar traits?
Why or why not?
How does a parent being homozygous for a trait affect the children?
How does a parent being heterozygous for a trait affect the children?
Explain how each of Mendel’s three laws was demonstrated here. What specific steps did we
do in the lab to represent each of Mendel’s principles?
Explain how genotype and phenotype are related.
How does the presence of multiple alleles affect the genotypes? The phenotypes? What is
meant by multiple alleles?
How does incomplete dominance affect phenotypes?
How does incomplete dominance affect the statistical outcomes?
Examine the genotypic and phenotypic ratios for ear shape and gender? How does this
compare with what you would expect to find without incomplete dominance?
In general, explain what happened in the lab overall. What did you learn? Why is this such an
important concept?
Explain any differences between the predicted outcomes and the actual outcomes.
Note: . It will probably take a minimum of two pages in the conclusion to fully explain this
lab.
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