In this lesson and the extensions provided the students should
have the opportunity to familiarize themselves with the relationship between
the DNA molecule, genes and chromosomes, and how each of these play an important
role in the processes of mitosis and meiosis. They will also have the opportunity
to perform two different hands on activities that will simulate the process
of meiosis and how genetic information is passed on from parent to offspring.
Some previous background understanding of the structure of the DNA molecule
and basic genetic terminology would be very helpful, to allow the students
to more fully understand the transfer process of genetic information. This
activity in addition to teaching genetic concepts could also provide several
opportunities to work with mathematical probabilities as they relate to
various genetic possibilities.
Our Human Body #3: What Are Cells Like?
Our Human Body #4: DNA Life's Controller
Students will be able to:
- discuss the role of DNA in genetics;
- describe the process by which cells reproduce;
- explain the difference between mitosis and meiosis;
- model the action of human chromosomes during meiosis and fertilization;
- analyze the patterns of inheritance that occur;
- compare expected offspring obtained using mathematical calculations
with observed offspring obtained through coin tossing.
Meiosis and Fertilization Activity
per pair of students
Phenotype Ratios with Two Traits Activity
- 1-pair scissors
- 1-bottle of glue
- 2-photo copies of six chromosomes for students to cut out
per pair of students
- two pennies
- two nickels
- small amount of masking tape
- marking pen
- Prokaryotic- a cell without a visibly evident nucleus.
- Eukaryotic- a cell having a visibly evident nucleus.
- DNA(deoxyribonucleic acid)- the molecular basis of heredity in organisms,
found in the cell nuclei of eukaryotic cells and constructed of a double
helix of nucleotides held together by hydrogen bonds.
- Mitosis- the first step of eukaryotic cell division; the nucleus divides
into two nuclei having identical genetic material. Meiosis- eukaryotic cell
division; each daughter cell has half the number of chromosomes of the parent
- Probability- the likelihood that an event will occur.
- Karyotype-a photograph showing the individual's chromosomes in homologous
To give students a specific responsibility while viewing remind
them that you will be pausing the video several times for review. The video
will have several places where a question will appear on the screen. Remind
the students they will be expected to answer the questions plus teacher
prepared questions at each of the pause locations.
Note to the Teacher: This video assumes students have a basic understanding
of the DNA molecule and its relationship to genes and chromosomes. If the
students background is such that they need to define these terms, it would
be best to review them before starting the video.
BEGIN the video Our Human Body #4 near the beginning
with sound and the title "Our Human Body; DNA: Life's Controller on
the screen. PAUSE after they ask the two questions," Why do
people have different colors of skin, hair and eyes?" " Why do
so many different forms of life exist?" Allow students to respond to
the questions. I prefer to accept all responses at this point.
RESUME the video and PAUSE when SciFax appears on the screen
with the question, "Can two brown-eyed parents have a blue-eyed baby?"
Allow the students to respond to the question. You may wish to show them
on the chalkboard how this is possible, if they do not understand how genes
are paired by this time. RESUME the video and PAUSE when the
word chromosome appears on the screen. At this time ask the students what
they think is the relationship between the terms DNA, genes and chromosomes.
You may also wish to introduce the terms haploid and diploid at this point,
if they are not already familiar with the terms. RESUME the video
and PAUSE when SciFax and the question, " How many codes for
genetic inheritance are there?" Allow the students to respond to the
question. Some additional questions you may which to ask at this time:"
How many yards of DNA does an average human cell contain?" " Who
were the three scientists mentioned that received a Nobel prize for their
work with DNA?" "Would a persons DNA reach to the sun and back?"
Challenge the students to calculate the number of miles of DNA in a human
body which may contain 60 trillion cells. FAST FORWARD to the point
where Human Genetics appears on the screen. RESUME the video and
STOP when the question, "How much of one's DNA is devoted to
genes?" appears on the screen. Allow students to respond to the question.
You may also choose to introduce the term karyotype at this point. Go to
the next video Our Human Body #3, What Are Cells Like? Have the video cued
to where the words "Cellular Reproduction" appear on the screen.
Teacher note: This is approximately 10 minutes into the video.
BEGIN the video with sound and PAUSE when the word "mitosis"
appears on the screen. At this point review with the students the difference
between asexual and sexual reproduction. RESUME the video and PAUSE
when SciFax appears on the screen along with the question, "Are cells
dividing in your body right now?" Remind students that millions of
cells divide in your body every second. RESUME the video and STOP
when the words "Instant Replay" appear on the screen. At this
time lead the students in a discussion that will allow them to compare and
contrast mitosis and meiosis. "How many chromosomes does each produce?"
"What organisms may use mitosis?" "What type of reproduction
uses the process of meiosis?" "Why is meiosis necessary for sexual
Meiosis and Fertilization Activity
Meiosis is the form of cell division that produces the special haploid cells
called gametes. In Meiosis chromosome are randomly shuffled. As a result
those organisms that reproduce sexually, have a mixture of the traits from
both parents. In humans, over 8 million genetically different gametes are
produced. In this activity you will determine genotypes and phenotypes for
gender, tongue rolling, earlobes, mid-digital hair, hairline and thumb shape.
Use the following criteria for the determination of which genotypes you
with to choose, in comparison to your lab partner. Hairline (widow's peak
is dominant, (WW or Ww), to recessive (ww), no peak); Thumb (curves back
is dominant (TT,Tt) to recessive (tt), straight); Tongue Rolling (Ability
to roll tongue is dominant (RR,Rr), to recessive (rr), inability to roll
); Ears (Lobed (LL,Ll) is dominant to recessive (ll), attached); Hands (mid-digital
hair (HH,Hh) is dominant to recessive (hh), lack of mid-digital hair), and
sex (female is XX and male is XY).
Teacher Note: Pictures showing these traits may be helpful, or have the
students see if they can identify each of the traits on each other.
In your lab notebook prepare a data table that will allow you to choose
one of each of the above genotypes and phenotypes. (Use all six traits).
Have your lab partner do the same, but choose different gene combinations.
Since you will be using these genotypes in a process representing fertilization,
try to make choices that will produce as much variety as possible.
Select your six chromosomes and write the corresponding genotype on each
chromosome.(See chromosome handout in appendix). Write the name of the characteristic
in the line where it is labeled phenotype. Put your name in the parent space,
to keep track of the chromosomes later in the activity.
Cut along the dotted line. Fold them in half and glue them together.
You and your partner should stand about one meter apart, facing each other.
Each should drop his or her chromosomes to the floor. Match the numbers
on the chromosomes with each other. Example: Put both chromosomes labeled
number one together. You should now have one of the following combinations
(WW,Ww,ww). Record in your notebook, the genotype and phenotype of the combined
chromosomes from each of the six pairs.
Repeat steps 5 and 6 two more times. Also record this information in your
notebook. This should now give your three "children".
You may wish to name "your children" based on the genotype combination
of the sex chromosomes.
Upon completion, answer the following questions:
Which step in the activity simulated the random assortment of genes that
occurs during meiosis?
Which step simulated fertilization?
List the traits which ended up being homozygous recessive.
List the traits that were homozygous dominant.
Could two children in a row have the same genotype? Explain.
What is the probability of your three children, all being either male, or
Does the combination of genes in the first child change what genes will
be available to subsequent children? Explain why or why not?
PHENOTYPE RATIOS WITH TWO TRAITS ACTIVITY
In genetics the probability of certain traits appearing in offspring is
often expressed as a ratio. For example, parents that are both heterozygous
for normal skin pigment(Aa) can produce two types of offspring, normal and
albino. The expected ratio in the offspring is 3:1. This means that for
every four children, three are expected to be normal and one is expected
to be an albino. In this activity you will substitute marked coins to substitute
for gamete cells and toss the coins to represent offspring.
Construct a Punnett square to represent the two characteristics, skin pigment
and body height. The parents genotypes are AaMm and Aamm.
Assume that capital letters represent dominant genes.
A=normal skin pigment; a=albinism(no pigment); M=normal body height; m=short
Determine the four phenotypes and how many offspring of each there are.
Based on the information in your competed Punnett square, complete the expected
column for 16 offspring in the correct column. Results of Cross Between
AaMm and Aamm
Phenotype Number Toss Results Total
combinations expected number
for 16 for 96 observed
Normal skin and
6. Mathematically determine the expected number for each trait and record
your response in the expected column for 96 offspring.
7. Obtain two pennies and two nickels:
a. cover both sides of two pennies and two nickels with masking tape.
b. mark an "A" on one side and an "a" on the other side
of both pennies.
c. mark an "M" and an "m" on one nickel, and an "m"
on both sides of the other nickel.
d. toss the four coins, the pennies in one hand and the nickels in the other
hand a total of 96 times. After each toss, record the phenotype that appears
in the appropriate column.
Answer the Following Questions, Based on Your Data in the Above Table:
Explain how the number of expected offspring compares to the number of observed.
What was the phenotype ratio in your completed Punnett square.
Is this a typical ratio of a dihybrid cross? Explain your answer.
Which of Mendel's Laws would tossing the pennies and nickels represent?
Give the ratio of your results of observed to the nearest whole number ratio.
Explain how the observed and expected offspring ratio might have compared
if only 16 coin tosses were used instead of 96.
Explain the need for using large numbers of observed offspring when
attempting to prove that genetic totals of expected results do agree with
What is the advantage of tossing and reading properly marked coins over
using living organisms?
If the ratio in #5 above is not 9:3:3:1, what could you do about the coin
tossing to arrive at a closer ratio?
Would you get a closer ratio by doubling your numbers in the 96 times column,
or toss the coins 192 times, and record the data? Explain.
Have a geneticist from the community talk to the class about
new technologies in the field of genetics.
If a dairy farm is located in your community, have someone come to class
and discuss the process of artificial insemination, and its advantages.
Visit a local nursery and have them explain the use of genetics in obtaining
numerous varieties of flowers.
Invite a pharmacist to class to talk about the use of genetic engineering
in the making of products such as insulin and the human growth hormone.
Invite a genetic counselor to class and discuss the probabilities of inheriting
certain genetic defects.
Have students write to various organizations such as the March of Dimes
and determine what new advances are being made in the battle against various
Math: Do a variety of ratio and probability problems.
Example: What is the probability that two people would have the same birthday
in a class of 25 students.
Science: Research the progress of the human genome project.
Industrial Technology: Construct a scale model of DNA showing the
double helix design.
Science and Social Studies: Discuss the possible benefits and hazards
of genetic engineering.
Science: Make slides from an actively growing onion root tip, stain
and observe under the microscope on high power.
Art and Science: Draw and label the various stages of mitosis.
Master Teachers: Dennis Reule and Cindy Yocum
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worksheet associated with this lesson.
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