Download Unit 3 Ch. 10 - Genetics In Action

IIT/FIELD MUSEUM – High School Transformation Project
Biology
Genetics in Action
Biotechnology – Pasta Critters
Glencoe Biology: The Dynamics of Life
Unit 3 Genetics
Chapter 10 Sexual Reproduction and Genetics
Sec. 10.2 Mendelian Genetics
Context of Lesson
The purpose of this lesson is for students to reinforce observation skills, data collection skills, data
analysis skills, and how to make evidence based conclusions all in the context of applying their
understanding of Mendelian genetics. Students should have completed section 10.2 in the Glencoe text.
Students will be asked to infer the inheritance pattern of two Pasta Critter traits. Students will
contribute their observations to the class data. After analyzing the data students will suggest a pattern
of inheritance to explain their observations. They will use evidence from their observations and what
they have learned about Mendelian inheritance to support their inferences. Students should be familiar
with the Punnett Square and with dihybrid crosses. This lesson acts as an evaluation of student
understanding of Mendelian genetics as well as developing student understanding of (and abilities in)
the Nature of Science and Scientific Inquiry.
Main Goals/ Objectives:
By the conclusion of the lesson students will be able to:
 Explain the crosses leading to dihybrid cross ( F2) generations
 Explain the ratio of phenotypes in a dihybrid ( F2) generation (9:3:3:1)
 Explain the different genotypes present in a dihybrid (F2) generation
 Infer that the combinations they observed represent the dihybrid (F2) cross
 Make observations, analyze data, and report results
 Make inferences based on evidence
 Distinguish between observations and inferences
Nature of Science: Integrated Theme
 Distinguish observations from inferences, explain that inferences should be based on
observation, and explain that the development of scientific knowledge involves both
observation and inferences so scientific knowledge is partially inferential.
 Explain how scientific theories are different from scientific laws: Scientific laws are more likely
observable patterns and scientific theories are explanations fro observable patterns.
 Explain that scientists’ work is influenced by social and cultural environments.
 Explain that scientific knowledge should be based on empirical data.
Scientific Inquiry: Integrated Theme
 Explain that scientific investigations all begin with a question, but do not necessarily test a
hypothesis.
 Explain that research conclusions must be consistent with the data collected.
 Explain that scientific data are not the same as scientific evidence.
 Explain that explanations are developed from a combination of collected data and what is
already known.
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Biology
Facilitation
The Pasta Critters should be prepared three days before the lesson so the dyed Pasta Critters will be
dried and ready for students to determine phenotype and genotype when performing the test cross.
The actual activity can be completed in 1 class period. The activity involves students observing the
variety of combinations which will be used to determine the genotypes of the parents based on the
phenotypes of the offspring. Day 2 will provide enrichment practice utilizing the dihybrid 2-trait plant
genetics with fast plants (computer simulation)
Materials (Teacher Preparation: 3 Days Before Lesson)
For each group of 2 to 4 students provide:
2 brown lunch bags
20 to 40 colored objects with identical size and shape such as seashell pasta
40 to 60 clear (or yellow) objects with identical size and shape, such as seashell pasta
20 to 40 different colored objects with identical size and shape, such as curly pasta
40 to 60 clear (or yellow) objects with identical size and shape, such as curly pasta
1 waterproof marker
Green and Orange food coloring
Review
Monohybrid One-trait test cross
Select pasta with the same shape to represent the alleles for head color of the parents. It is preferable
to have one object that is relatively colorless to represent the recessive allele and one that is colored to
represent the dominant allele. This activity uses round, colored pasta to represent the dominant allele
and round colorless pasta to represent the recessive allele.
Dihybrid Two-trait test cross
For a two-trait cross, use two different pasta shapes to set up the bags. Label the bottom of the bags
with the set numbers so you know which set of alleles each group receives and to see if their results
correspond with the predictions.
The Lesson
Day 1
Bell Ringer
Place the transparency of the coins on the overhead. Ask students “What possible combinations can
result from combining one coin from each group? What is the ratio of the possible combinations? Ask
students if they think there is a dominant or recessive trait. The teacher should gather student ideas.
Textbook definitions are not as good as accurate descriptions in the students’ own words.
Activity
Distribute Student Pasta Critter Data Sheet
In a test cross, an organism showing the dominant trait is mated with (or crossed with) an organism that
has 2 recessive alleles for the trait (*homozygous recessive). In the Pasta Critters example, alleles for the
green pasta represents the dominant green allele (big “G”), and the clear or cream pasta represents the
recessive clear allele of the imaginary Pasta Critter (little “g”}.
Before the activity, have students predict the outcomes of each possible cross between green and clear
Pasta Critters with a Punnett square.
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Biology
Students receive an assigned cross, using 2 bags. Each bag represents one of the parents and contains
pieces of colored pasta that represent the parent’s alleles. Students draw one piece of the pasta from
each bag to simulate the outcome for possible offspring. This is done 20 times. The alleles and
appearance of each offspring is recorded, tallied, and compared to the offspring predicted by using a
Punnett square.
Review with students ratio and percentages as they collect their data.
The predicted results can be described as a ration, fraction, or percentage. In this case, the ratio of allele
combinations for the offspring (genotype) is 1 GG:2 Gg: 1gg, which means 1 homozygous dominant to 2
heterozygous to 1 homozygous recessive. This can also be described as ¼ (or 23%) homozygous
dominant, ½ (or 50%) heterozygous, and ¼ (or 25%) homozygous recessive.
The appearance (phenotype) ratio of the offspring is also important. In this case some offspring would
be green (G, or Gg) and some will be yellow (gg). The ratio would be 3 green to 1 yellow. The fractions or
percentages would be three fourths (or 75%) green to one-fourth (or 25%) yellow.
Monohybrid Test Cross #1
In Test Cross 1, homozygous dominant is crossed with the homozygous recessive. All offspring are
heterozygous and express the dominant trait of green. (100% Gg)
Monohybrid Test Cross #2
In Test Cross 2, a heterozygous dominant (Gg) is crossed with a homozygous recessive (gg). Half the
offspring are heterozygous, expressing the dominant green trait, and half are homozygous recessive,
expressing the clear color. (50% Gg, 50% gg)
Review genetic terms before proceeding to Dihybrid Test Cross 3.
Review with students the terms gene, allele, phenotype, monohybrid and dihybrid cross, dominant and
recessive.
Show students the 2 bags with the one Pasta Critter that has a green head (G) and orange body (R), Ask
students to Predict the possible allele combination for each Pasta Critter that the bag represents.
Ask them, “If you find a Pasta Critter with a green head and orange body, how can you determine the
combination of the alleles?” and “If 2 green-head, orange body Pasta Critters mate, would all their
offspring be green head with orange bodies, or could they produce green head, clear/yellow body
offspring? Or any other colored organisms?”
Provide students with the following instructions, “Each group will receive 2 bags. One will represent the
alleles for a green head, orange body Pasta Critter, and the second will represent the alleles for a
clear/yellow head, clear/yellow body Pasta Critter. Two alleles from each bag will be contributed to the
offspring to represent what would be passed on from each parent in the egg or sperm. Shake the bag,
and without looking, pick a round piece of pasta and a squiggly piece of pasta to represent the alleles
contributed for each trait from each bag. Ask What is the proportion of allele combinations?
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Dihybrid Test Cross #3
In Test Cross 3, students receive an assigned cross, consisting of 2 bags. One bag with 1 of each pasta
shape represents the alleles of 1 parent; a second bag with one of each pasta shape represents the
alleles of the other parent. Each student (or group) draws one of each allele shape from each bag to
represent the parents’ contribution for the trait of the offspring. (G=green head, g=yellow head,
R=orange body, r=yellow body.)
The teacher should collect the data from each group showing each kind of phenotype. A member from
each group could record the group data on the board or the teacher could record the data on an
overhead/the board.
Class Discussion Questions to Determine the Pattern of Inheritance
Ask, “Why are we adding up the data from each group?” Students should respond that the more data
they have the more evidence they have for their inferences about the pattern of inheritance.
Ask, “From the class data, which phenotype is greatest in number? Which is least?”
Ask, “Which traits do you think are dominant? Which are recessive? How can we tell?” No matter what
the students answer, ask them to explain what evidence they used to come to their decision. Guessing
should be discouraged. Students should suggest explanations for the ratios of the phenotypes. Some
students might calculate the ratios for each of the phenotypes.
Ask students to calculate the ratios for each phenotype, for example:
# of Pasta Critters with Green heads and Yellow Bodies
total # of Pasta Critters
The ratios should exhibit the 9:3:3:1 ratio seen in dihybrid crosses. Ask “Where have you seen this kind
of ratio before?” Dihybrid crosses.
Ask “If this is the F2 generation, what was the genotype of the F1 generation? The phenotype?” If you
haven’t already, introduce an agreed upon notation for the dominant and recessive traits, such as that
described in the Teacher Background Knowledge section. Answers should be that the F1 generation was
Green Head and Orange Body , all GgRr. Ask, “What were the genotypes and phenotypes of the Parental
generations?” GGRR X ggrr. Lastly, ask students, in their groups, to conduct the Parental cross and the
F1 x F1 cross using the Punnett square. Students should display all the genotypes for the F2 generation
and match them to the phenotypes they observed in the Dihybrid Test Cross 3.
Day 2
Bell Ringer
Place the transparency of the seedling structure on the overhead. Ask students to label the parts of the
seedling on the overhead using the list of parts in the bottom corner. Ask them to briefly describe, in
their own words, what they think is the role of each of the seedling parts. The teacher should gather
student ideas. Textbook definitions are not as good as accurate descriptions in the students’ own words.
Distribute the Computer Prediction Sheet
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Teacher Background Knowledge:
There are two traits expressed in the following seeds:
Trait R/r
R = standard height
r = rosette-dwarf
Rosette-dwarf is a recessive trait to standard height. The designation for this trait is rosette-dwarf: ros,
standard: ROS. We will use “r” and “R” respectively.
Trait A/a
A = standard Purple stem
a = non-purple stem (green)
Non-purple stem is recessive trait to standard (purple) stem color. The designation for this trait is nonpurple: anl, standard: ANL. We will use “a” and “A” respectively.
P Generation  F1 x F1  F2 Generation
During this lesson students will be viewing the F2 generation.
Here are the crosses that produced the F2 generation:
P generation:
RRAA x rraa =
F1 generation all RrAa
F1 x F1:
RrAa x RrAa =
F2 generation, arranged by phenotype/ratio:
(9) Standard height/Standard Purple stem
RRAA
RRAa
RrAA
RrAa
F2
Generation
9:3:3:1
(3) Standard height/Non-purple stem
RRaa
Rraa
(3) Rosette-dwarf/Standard Purple stem
rrAA
rrAa
(1) Rosette-dwarf/Non-Purple stem
rraa
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Day 2: Two-Trait Plant Genetics with Fast Plants (computer simulation)
Materials
One computer for every two students
Computer Prediction Sheet (see link below)
Computer Data Sheet (see link below)
Part 2
Conducting the Simulations
Students ideally can complete the project in groups of two, either at the computer lab or with a
classroom set of laptops. However, the computer simulation could be completed as a class, with the
teacher projecting the simulation in the classroom and students recording data from the simulation.
If the students haven’t completed the Computer Prediction Sheet for homework, have them do so at the
start of class. Students will make predictions for the crosses they will conduct during the simulation
using the following Computer Prediction Sheet:
http://www.fastplants.org/genetics/pdfs/ModelPred.pdf
The Simulation can be found at the following website:
http://www.fastplants.org/genetics/Introductions/index.htm
At this site you will find three simulations. Select the Two-Trait Plant Genetics simulation, number 2.
Number 3 might also be interesting to try with more advanced students. Be aware that after selecting
the simulation, the first page you will see is an instructions page. Read carefully and then scroll to the
bottom to find the link to the simulation.
Instruct the students to conduct the crosses at the simulation website using the following Computer
Data worksheet to record their findings: http://www.fastplants.org/genetics/pdfs/CompXDataSheet.pdf
Evaluation
The teacher will assess student understanding during Part 1 by looking at the work each group produces,
as well as student answers to the class discussion questions. Student Prediction and Data sheets from
Part 2 are also forms of assessment of student understanding.
Modifications/ Accommodations
Pairing challenged students with regular education students is an appropriate accommodation if
students will be working in pairs or in groups. Challenged students should be allowed to answer orally or
to make drawings of their ideas. A teacher can complete portion of the Computer Prediction sheet with
students and then let students practice on their own. Likewise students who need more help can follow
along as the teacher manipulates the simulation. Students can record the results on their Computer
Data sheet.
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Extensions:
 Fast Plants will complete a life cycle, producing seeds, in just 40 days. See the following link to
learn about other genetic variants, to learn how easy it is to maintain the plants and how to
cross them for continued study of genetics, plant anatomy, etc:
http://www.fastplants.org/intro.php
 Conduct a similar exploration during Section 12.3 using the Variegated Fast Plant seeds. The
BioLab on pg. 330-331 explores cytoplasmic inheritance (chloroplast DNA). In the case of the
Variegated variety, a mutant gene found in the chloroplast DNA of the ova lead to blotchy leaves
in the offspring.
 Transfer the seedlings to soil and observe them for growth and development as well as
reproduction in preparation for or as part of Unit 7. See the following lesson, “An Inquiry
Approach to Wisconsin Fast Plants”:
www.csip.cornell.edu/Curriculum_Resources/CEIRP/Fast_Plants.doc
 Reinforce photosynthesis principles by conducting a lesson to see the effects of different
variables such as light intensity, light color, temperature, water, soil, and pH on Fast Plant
growth.
 A reusable set of 30 dihybrid corn ears can be purchased from Carolina Biological. There are two
traits with two alleles each. (P) for Purple color is dominant to yellow seed color (p). (S) starchy
kernels are dominant to those with low starch and more sugar (s). The (S) are full and round
while the (s) have a wrinkled appearance. Students can count the various phenotypes and
determine they follow a 9:3:3:1 ratio. See the following website for info and to order the Corn
Dihybrid Genetics BioKit:
https://www2.carolina.com/webapp/wcs/stores/servlet/ProductDisplay?jdeAddressId=&catalo
gId=10101&storeId=10151&productId=4344&langId=-1&parent_category_rn=&crumbs=n
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Seedling Structure
Seedling Parts
Roots
Seed leaves (cotyledons)
Stem
Adult leaves
http://etc.usf.edu/clipart/4700/4740/seedling_8.htm
File Name: seedling_8
Description: A more advanced seedling of the cherry.
Source: Asa Gray, How Plants Grow, A Simple Introduction to Structural Botany (New York:American Book Company, 1858)
Keywords: Botany, seed, seedling, cotyledon, cherry
Copyright: 2003, Florida Center for Instructional Technology.