Biology Lesson: Traits and Inheritance
Biology 501, Summer 2007
Revised Lesson: August 13, 2007
Instructors: Dr. Ingrid Waldron
Jennifer Doherty
TA: Jennifer Tareila
Group Members:
Theresa Lewis-King,
Candace Randolph, and Bill Wagenborg
Biology 501
Summer 2007
Revised Lesson:
August 13, 2007
Instructors: Dr. Ingrid Waldron
Jennifer Doherty
TA: Jennifer Tareila
Group Members:
Theresa Lewis-King, Candace Randolph, and Bill Wagenborg
Biology Lesson: Traits and Inheritance
Lesson Plan Overview:
Human beings pass particular
characteristics from parent to offspring in an orderly process accomplished by
means of their genetic codes, which are contained in the DNA of fertilized egg
or sperm cells. Some characteristics will influence a studentÕs physical
appearance and others will not. Some children will resemble their parents
because of these inherited traits. However, even if children do not physically
look like their parents, they still have inherited genetic characteristics from
their parents.
Unit Objectives:
Students will learn:
Why
teach this Lesson?
School District of Philadelphia
7th Grade Core
Curriculum
Unit of Study: Cell, Heredity, and Classification
Objectives:
Pennsylvania Science
Standards
PA Standard:
Unifying Themes
PA Standard:
Inquiry and Design
PA Standard:
Biological Sciences
(School District of Philadelphia. Science Core
Curriculum, 2004)
Background For Teachers
Heredity and Inherited
Traits Lesson
Theresa Lewis-King, Candace Randolph, and William
Wagenborg
The process of instruction involving an organismÕs inherited traits should attempt to make clearer to students why some children resemble their parents and others do not. In this lesson, recognizing vocabulary is important, however being able to understand the processes and roles involved is the main goal. This information should be used to help students understand:
It is also important to recognize that although this information is being applied to human beings, it is also true for plants and other animals (Cummings, 2006). Human beings, like all living things, inherit their characteristics from their parents. These traits are passed on through a process that starts with meiosis in each parent and finishes with fertilization of a motherÕs egg from a fatherÕs sperm. The humanÕs individual characteristics and makeup depend on the variation of the gene that he or she receives from each parent. (Cummings, 2006)
As discussed in meiosis, the human gametes, sperm cells in males and egg cells in females, each contain twenty-three chromosomes. When the sperm and egg cell join in fertilization, a zygote containing forty-six chromosomes, twenty-three from the mother and twenty-from the father, is produced. These chromosomes contain genes that provide the ÔblueprintÕ for the developing embryo. The embryo has a pair of genes, one from each parent, which is responsible for specific characteristics. Each gene may contain different alleles, alternative versions of the same gene, for a particular characteristic. For example, an allele for the eye color gene might code for brown eyes, blue eyes, or hazel eyes. The trait that the infant will have when born is determined by the specific combination of alleles that it received from its parents (Oxford University Press, 2004).
In this lesson, we focus on two important classifications of gene alleles that determine a humanÕs biological and physical makeup, dominant or recessive. Dominant alleles code for proteins that perform specific functions in the cell and recessive alleles code for proteins that are either non-functioning or have little effect on the cell (Oxford University Press, 2004). For example, the gene that codes for a protein that produces the pigment melanin that affects skin color on chromosome 11 could have two alleles, the allele for the normal production of melanin (skin color), and the allele for non-production of melanin. The normal producing melanin allele is considered a dominant allele because it codes for a protein to produce the pigment for melanin. The non-melanin producing allele is considered recessive because it codes for a protein that does not produce the pigment for melanin. A dominant allele is expressed in humans when both the paternal and maternal alleles of his/her gene are dominant or if one of the alleles is the dominant and the other is recessive. If both the mother and fatherÕ gamete or one of their gametes provide the allele for the normal producing melanin, the child will have normal skin color. Consequently, the recessive allele is expressed in a human when both the paternal and maternal alleles are recessive. The mother and the fatherÕs gametes would both provide the allele for non-producing melanin and thus would result in albinism (white skin color and hair) in the child Cummings, 2006).
This link provides a list of common dominant and recessive traits in human being
http://www.blinn.edu/socialscience/LDThomas/Feldman/Handouts/0203hand.htm
(Thomas, 2007).
An organism is homozygous for a trait when they possess two of the same allele, one maternal and one paternal, for a gene. This is true when both alleles are either dominant or recessive. An organism is heterozygous for a trait when they possess a dominant and a recessive allele for the same gene, in which case the dominant trait will be the expressed trait. If an organism is heterozygous, they will still have two copies of a gene, they are carriers of a recessive gene, even though it is not expressed. In this way a parent could pass along a trait to their child without it ever becoming apparent. This is important to the understanding of how disorders, such as Sickle Cell Anemia, can occur in a child after it has been carried and passed from previous generations without affecting them. (Oxford University Press, 2004)
Knowing the genetic make-up of the parents allows us to make prediction about the possible genetic makeup of the offspring. Using a table called a Punnett Square, it is possible to predict the possible character traits of the offspring. In order to identify and predict genetic traits, each gene is assigned a letter. If the allele for that gene is dominant, an uppercase letter is written. If the allele is recessive, then a lower case letter is written. For example, the melanin producing allele would be labeled ÒAÓ because it is dominant and the non-melanin producing allele would be labeled ÒaÓ because it is recessive. The grid, developed by R.C.Punnett, is constructed based on the number of all possible combinations of paternal and maternal alleles for particular genes. Generally, a parent only has two alleles for any one gene. To determine the number of square grids needed to compute the Punnett Square, multiply the number of possible egg genotypes by the number of possible sperm genotypes. For the purposes of this lesson, we are focusing on alleles of one gene, two alleles from each parent. Thus the grid will be 2 x 2 or 4 squares. Although it does not have an effect on the outcomes, consistency in the placing of the maternal and paternal alleles on the grid may help studentsÕ organization. The paternal alleles for example, are always listed horizontally on the grid, one above each block and the alleles of the maternal gene are always listed on the grid vertically, one next to each block. The paternal and maternal alleles are then put into pairs of two based on their location on the grid (Oxford University Press, 2004) (Friedman, 2004).
Below is an example of the use of A Punnett Square in predicting albinism in children.
Mother Aa (heterozygous gene-dominant- normal melanin production- she has normal
skin color, but is an albinism carrier)
Father Aa (heterozygous gene- dominant – normal melanin production- he has normal
skin color, but is an albinism carrier)
A
a
AA Melanin produced |
Aa Melanin produced |
Aa Melanin produced |
aa no melanin
produced-albinism |
A
a
This Punnett Square shows that each child has a 75% chance of normal skin color because three of the four quadrants show that the dominant trait would be expressed (AA, Aa and Aa). This Punnett Square also shows that each child has a 25 % chance of having albinism because one of the four quadrants shows that the recessive trait would be expressed (aa). The Punnett Square can be used for all allele pairs for all genes. It is not meant to be an exact calculation of what the individual offspring of these parents will be, but rather an expression of possibilities because it represents an exact calculation of probability. All of the children born to these two parents have the same probability of inheriting normal skin color and albinism because each pregnancy is an independent occurrence and the probability remains the same. This illustrates a very important concept that is a key to understanding heredity: there are traits that may appear in a child that do not appear in either of his/he parents or his/her siblings. (Friedman, 2004)
The genetic makeup of a human is the genotype based on the alleles that he/she obtains from his/her parents. The phenotype is the expression of the genotype modulated by the environment (Oxford University Press, 2004). The genotype is an organismÕs genetic make up. Specifically, it is the complete set of genetic information in every body cell of the organism. This genetic representation is inscribed in every humanÕs DNA and is replicated throughout the body. It is the listing of possible alleles for genes inherited from the mother and father that allow us to use a Punnett Square to predict the possible genetic makeup of the offspring. The phenotype is the observable characteristics of any organism that are determined by its genotype combination of alleles. These traits determine a humanÕs physical appearance, hair color, eye color, height, skin tone, etc. Along with genotype, the interaction a human has with the environment can play a crucial role in determining a personÕs phenotype. Factors such as diet, geography, (surroundings and climate) and physical activities can change or alter someoneÕs phenotype. For example, Phenylketonuria (PKU) is a recessive disorder associated with the bodiesÕ inability to metabolize an essential amino acid, phenylalanine. In Infants who are homozygous for PKU, phenylalanine builds up to toxic levels in their cells and causes severe mental retardation and other developmental problems. If the infant is given a restricted diet low in phenylalanine and maintain this diet throughout life, then the toxic affects of phenylalanine is reduced in the cell and some developmental delays can be avoided. This shows how the environment can affect a humanÕs phenotype (Snustad, 1997).
The Human Genome Project, completed in 2003 funded by the U.S. Department of Energy and the National Institutes of Health, is a way for the science world to examine human DNA and identify the estimated 30,000 genes that are present. This research will be used for a variety of reasons that include: understanding the different functions of DNA, shedding light on different genetic diseases and providing more of a basis for human identification through DNA samples that can used in such things as criminal cases. The project itself is finished, but the analysis of data will go on for some time. As more is learned from the data, a better sense of human genotype will be developed. (HGMIS, 2006)
Although we may understand a lot about human traits and inheritance, there is still more to be discovered. Students need to be aware that learning about heredity, like all of things in science, is an ongoing process. Many of their questions may be answered, but many more may arise.
Grade Level 7 Science: Traits
and Inheritance
Approximate Class Time:
Five Class Periods (45 minute periods)
Big Idea: Why do
some children resemble their parents more than others?
Lesson Structure:
The School District of Philadelphia
uses the Benchmarks for Science Literacy developed by the American Association
for the Advancement of Science (AAAS) and the National Science Education
Standards developed by the National Research Council to provide teachers a
framework for science instructions. The overall goal is to provide students
with an opportunity to fully engage in the learning process by asking
questions, making predictions, conducting experiments and investigations,
analyzing data, using technology, communicating using acceptable scientific
language.
This lesson will follow the Science
of Philadelphia K-8 Instructional Model. (The School District of Philadelphia,
2004):
á
Engage
á
Explore
á
Explain
á
Extend
á
Evaluate
Student Background
Knowledge
Lesson#1:
Misconceptions: Students may think that if they look more like one
parent, then they have more of that parentÕs genes. Students sometimes believe
that they have inherited traits from only one parent or the other. (Holt, et.
al, 2005) It is important that the teacher is aware of what students already
know because research on how students learn stress the importance of
identifying the concepts that students bring with them into the classroom. When
confronted with new information, it is believed that students will either; 1.)
Totally delete prior knowledge in favor of new information, 2.) Modify or
change the prior knowledge so it is in line with the new information, 3.)
Modify or change the new information so it is in line with the prior knowledge,
4.) Totally reject the new information. (Sewell, 2002)
Engage: During this part of the lesson, the teacher should
raise questions that will hopefully get students interested in the topic of
study. This part of the lesson will also give the teacher an idea of what
students already know, and also insight into misconceptions that might
interfere with students learning new concepts.
Warm-up Activity
Teacher: Record responses on chart paper and put the studentÕs name beside their idea. Look for possible themes that can be grouped together, this will indicated general areas of misconceptions. At the end of the unit, it is important to revisit these responses with students to determine if and how any of their original ideas have changed.
Teacher asks:
Group Activity: Clothing Combos
Teacher: Make a Class Chart, record student combinations
Wrap-up questions:
Journal Reflections: (children can share reflections if time permits)
Lesson #2: Teacher Directed Lesson
Explain: This part of the lesson is a formal
introduction of key concepts and vocabulary that students will need to
understand and achieve the learning outcomes stated in the lesson objectives.
Students should have an opportunity to ask questions for clarification, explain
concepts in their own words, and do additional research.
Teacher: Whole-Group Lesson
Unit Vocabulary:
Teacher: Introduce and discuss key vocabulary
terms, give students examples where appropriate and allow times for students to
add words to science journal.
*Student should create and maintain a science journal that contains key
vocabulary and concepts in words, pictures, diagrams, and formulas.
Wrap up: Homework Assignment:
Lesson
#3 and #4: Hands-on Lab Traits and Inheritance
Engage:
Teacher states: Many
times children and adults wonder why they do or do not resemble their parents.
As you have learned, you inherit genes from your parents that determine
specific characteristics such as their complexion, hair texture, and the
structure of your nose, eye color, and many more numerous characteristics.
Where are your genes located in
your body?
Student should make the connection
that genes are part of DNA molecules and DNA molecules are contained in the
chromosomes located in the nucleus of the cell.
How does a child inherit genes
from his or her mother and father?
Students should be able to explain
the process of meiosis, how a child gets twenty-three chromosomes from the
mother and twenty-three chromosomes from the father.
In todayÕs lab, we will consider
a very common characteristic in people, cheek dimples.
Explore: Allow students to work together in groups to
generate and test ideas that they may have concerning the topic of study.
Explain: Students should be able to ÒshowÓ what they know.
This is the part of the lesson that gives students an opportunity to do a hands
on lab designed to increase their understanding of key concepts.
Activity One:
Cheek Dimples are a very common
characteristic in people. One allele for the gene that codes for cheek dimples
is given the symbol ÒDÓ. The other
allele that codes for no dimples is given the symbol ÒdÓ. A person that has cheek dimples will have a
genotype of either DD (homozygous)
or Dd (heterozygous). Both of
these combinations of alleles will result in a child with dimples.
Why will both of these
combinations produce a child with dimples?
A person without cheek dimples will
have a genotype for dd (homozygous).
Why will this combination result
in a child that has no dimples?
Biologists use a Punnett Square to help show the possible genetic combinations of
zygotes. The alleles for each parent must be crossed with the other. For the
purposes of this lesson, we are focusing on alleles of one gene, two alleles
from each parent. Thus the grid will be 2 x 2 or 4 squares. The paternal
alleles are listed horizontally on the grid, one above each block and the
alleles of the maternal gene are listed on the grid vertically, one next to
each block. The paternal and maternal alleles are then put into pairs of two
based on their location on the grid (Oxford University Press, 2004) (Friedman,
2004).
Father (sperm)
Mother (egg)
|
D |
D |
D |
|
|
D |
|
|
Each square that you crossed
represents a possible offspringÕs genotype.
How many have the genotypeÉ
DD _____
Dd _____
dd _____
What fraction of them is? DD
_____, Dd ________, dd _________
How many of these offspring will
have dimples? Why?
Given the parentÕs genotype,
will any of the offspring have no dimples? Why?
In the above example, both parents
have the same allele for the gene that codes for cheek dimples, however there
are other combination of gene alleles that parents can possess.
What are some other possible
combinations that two parents could have?
Let examine another possible
parent combination.
Father (sperm)
Mother
(egg)
|
D |
d |
D |
|
|
d |
|
|
Each square that you crossed
represents a possible offspringÕs genotype.
How many have the genotypeÉÉ
DD _____
Dd _____
dd _____
What fraction of them is? DD
_____, Dd ________, dd _________
How many of these offspring will
have dimples? ______.
What are their genotypes?
________, _________.
How many of these offspring will
not have dimples? ______.
What are their genotypes?
_________.
Given the parentÕs genotype,
will any of the offspring have no dimples? Why?
Extend: Allow
students to use what they have just learned. They can apply this information to
an example that they make themselves.
Father (sperm)
Mother (egg)
|
|
|
|
|
|
|
|
|
Each square that you crossed
represents a possible offspringÕs genotype.
How many have the genotypeÉÉ
DD _____
Dd _____
dd _____
What fraction of them is? DD
_____, Dd ________, dd _________
How many of these offspring will
have dimples? ______.
What are their genotypes?
________, _________.
How many of these offspring will
not have dimples? ______.
What are their genotypes?
_________.
Write the phenotypes (will the
child have dimples or no dimples?) for
each set of alleles, and draw a picture to represent it.
DD Dd dd
_______________ _______________ _______________
Explain how two individuals with
the same phenotype can have different genotypes?
Activity Two:
Genotype Probability
Because children receive half of
their genetic makeup from each parent, biologist can use their understanding of
probability to predict the possible outcomes of a childÕs genotype and therefore their phenotype. However, random variation in which sperm will
fertilize which egg may produce very different results from the predicted
outcome.
What can be done to control for
random variation?
The Punnett Square below
illustrates the possible combinations of genotypes when both parents are
heterozygous for cheek dimples, ÒDdÓ.
Father (sperm)
Mother (egg)
|
D |
d |
D |
DD |
Dd |
d |
Dd |
dd |
What fraction of this coupleÕs
children will have a genotype of ÒDDÓ? __________
What fraction of this coupleÕs
children will have a genotype of ÒDdÓ? __________
What fraction of this coupleÕs
children will have a genotype of ÒddÓ? __________
The fraction of different genotypes
can be expressed in the ratio, 1:2:1.
What is the probability (change
the fractions to percents) of the following outcomes?
DD ________
Dd _________
dd ________
Explore: Allow students to work together in groups to
generate and test ideas that they may have concerning the topic of study.
In this activity, we will use a
two-side coin to help simulate the random assortment of gene alleles. There is
a 50-50 chance that egg or sperm cell will have the ÒDÓ or ÒdÓ allele.
|
DD |
Dd |
dd |
First four offspring |
|
|
|
Second four offspring |
|
|
|
Third four offspring |
|
|
|
Fourth four offspring |
|
|
|
Total |
|
|
|
|
/16 |
/16 |
/16 |
Predicted fractions from
Punnett Square |
|
|
|
Wrap-up Hands-on Lab
á
Students complete activity sheets and discuss their
results in-group.
Lesson adapted from: North Central Regional Technology in
Education Consortium.
Genetics, Dr. Scott Poethig, Dr.
Ingrid Waldron, and Jennifer Doherty, Department of Biology, University of
Pennsylvania.
Lesson #5
Evaluate: Evaluation of student learning is an ongoing process
during these lessons. The teacher will have numerous opportunities to listen
and observe students as they talk and interact with each other. There will also
be formal assessment that will provide feedback for the students to heal them
monitor their own learning.
Formal Assessment:
References
Online.
Oxford University Press. University of Pennsylvania. 7
July 2007 http://www.oxfordreference.com/views/ENTRY.html?subview=Main&entry=t6.e147
Australia:Thomson/Brooks/Cole.
Evolution. Ed. Mark Pagel. Oxford University Press 2003.
University of
Pennsylvania. 11 July
2007 <http://www.oxfordreference.com/views/ENTRY.html?subview=Main&entry=t169.e267>
Human genome project information.
Retrieved July 14, 2007 from
www.ornl.gov/sci/techresources/Human_Genome/home.shtml.
History, Mathematics, And Science In The Classroom. National Research
Council
the National Academies. The National Academies Press. Washington, D.C.
Extensions of mendelism Principles of genetics. New York: John Wiley& Sons