MEIOSIS AND PUNNETT SQUARES
Teachers: Joy Paul, Joy Bryson, Kathleen Tait, and Paul McNally
Grade level: Eighth Grade
Student Misconceptions based on the research:
a. Separation of homologous chromosomes (meiosis I)
b. Separation of sister chromatids (meiosis II)
c. Incorrect gamete formation in Punnett Squares
d. Replication of DNA
Life Science Standard C from NCES:
-Understand ideas about reproduction and hereditary
-Hereditary information is contained within genes
-Half of the genetic information comes from the father and half from the mother
a. Students will understand the process of meiosis in the genetic variation of
b. Students will understand that meiosis takes place in specialized cells in the
a. Students will describe the steps in the process of meiosis
b. Students will be able to describe the differences between a haploid cell and
a diploid cell
c. Students will be able to identify and differentiate between a somatic cell and a
gamete cell and a genome
a. Students will have an understanding of mitosis and the process of mitosis in
b. Students will be acquainted with the terms DNA, genes, chromosomes and
Anticipation of Questions
We expect students to have difficulty with the process of meiosis. Some of the questions we anticipate the students asking are as follows:
-Why doesnÕt each gamete cell contain 23 pairs of chromosomes?
-How do the chromosomes know which side of the line they should be on to split?
-What is a homologous chromosome and how is it different from a chromotid?
-Why isnÕt meiosis like mitosis?
We are sure that more questions will arise as the lesson proceeds.
Each group will consist of three students
-4 one-inch balls of modeling clay of four different colors: red, blue, yellow and green
-1 large oval cut from white paper
-4smaller ovals cut from white paper
-1 pair of scissors
-1 2.5 feet of thick brown yarn
-4 1 ft lengths of thick brown yarn
-1 1ft length of white string
Who do you look like, your mom or your dad?
How do we get to resemble one parent more than the other?
Why is there sometimes a mix of looking like both parents?
Students will view a simulation of Meiosis as presented on KroghÕs Biology CD-Rom
Students you are going to study the process of meiosis by working with chromosomes from a mythical organism known as Sevenia. Sevenia has a diploid chromosome with a number of four. You will follow these procedures until you are able to complete the process without the need of instruction.
1. Place the large white oval paper in the center of your table. The boundary of the paper is the cell membrane. This oval represents one precursor sex cell of the Sevenia.
2. Now you will set up the genome. You are going to create a diploid nucleus, which will contain two pairs of chromosomes. Take one stick of colored clay and divide it in half.
3. Take one half of each ball and roll it between your hands to form an elongated piece like a snake. You will have four chromosome models. Make the green and yellow chromosomes about four inches long and the red and blue pair about 6 inches long. The yellow/green pair is Pair 1 and the red/blue is Pair 2.
A chromosome is a tightly coiled strand of DNA and within each chromosome there are many, many genes. The chromosomes within each pair are homologous. Homologous chromosomes contain the same in size and function but they do have different alleles. For instance, the homologous chromosome may contain the same gene such as eye color but the allele form might be for one blue and the other brown.
4. We will look at four traits of the Sevenia. We will look at their location
on each chromosome. With a marker place write a G at the top of the green chromosome and a c at the bottom. On the yellow chromosome write a g at the top of chromosome and a C at the bottom. For the blue chromosome, write a B at the top and an L at the bottom. For the red chromosome, write a b at the top and an l at the bottom.
Genes on PAIR 1
Genes on PAIR 1
G (green fur)
c (straight fur)
g (yellow Fur)
C (curly fur)
Genes on PAIR 2
Genes on PAIR 2
B (blue eyes)
L (long eyelashes)
b (red eyes)
l (short eyelashes)
Remember that we are looking at two pairs of alleles on two genes
Each chromosome is replicated by DNA replication. Create a matching
chromosome, same shape and color by using the remaining clay.
Connect sister chromatids together at the centromere by pinching them
Question: How many chromatids are present in the nucleus after DNA replication? How
6. Prophase I
Pair up each newly replicated chromosome with its homologous chromosome. You will now have two tetrads that contain 4 sister chromatids each, 8 chromatids in all.
Now that the homologous chromosomes are near each other, crossing over can occur. In each tetrad, trade one allele between two non-sister chromatids by overlapping chromosome arms to form a crossover.
Break the clay to separate chromosomes and join the exchanged parts to their new chromosomes.
6. Metaphase I
Nuclear membrane has broken down in your cell.
Line the two tetrads end to end across the center of the cell.
Attach a piece of black yarn representing spindle fiber stretching from the centromere of each chromosome to the end of the cell nearest to it.
Question: Was there a reason why the red chromosome ended up on the same side as the
green chromosome, or was it random? Why or why not?
7. Anaphase I
Separate each tetrad and use the spindle fibers to move the homologous chromosomes to opposite poles of the cell.
8. Telophase I
Cytokinesis (cell division) occurs to form two daughter cells. These daughter cells are either haploid or diploid, but rather exist in some intermediate stage.
Question: Are the two daughter cells identical (in genetic make-up)? Why or why not?
9. Prophase II + Metaphase II
Line up the chromosomes in each cell end to end along the centerline. Attach spindle fibers to the centromeres.
10. Anaphase II
Separate the two sister chromatids and use the spindle fibers to move them to opposite poles.
Question: In anaphase II, what must happen to the centromere region?
11. Telophase II
Cytokinesis occurs again, producing a total of four daughter cells.
Are these cells haploids?
Write the genotype beneath each of the resulting daughter cells in the diagram above.
Students will discuss the answers to the questions presented in the lab. Students will also discuss any confusion they may have concerning the process of meiosis. At this point, the purpose of the activity must be discussed. The teacher may ask the students the questions presented In the beginning of the activity to demonstrate students understanding of the lesson. The questions were as follows:
Why do you resemble one parent more than another?
Why do you look like you mom or your dad?
How can you resemble both of your parents?
By refocusing the questions at the end of the lesson, students will demonstrate the level of understanding that they have achieved from this activity.
The next step to take in the process is taking this information and making Punnett Squares to find out the number of possible zygotes one could have when the sperm fertilizes the egg.
Students will create a flipbook that shows the process of meiosis step by step. Students will be provided with blank template pages in which they will illustrate the steps In the process of meiosis. See attached forms.
The following is the rubric to be used in the assessment.
Rubric ID: 1250162
Created: March 15, 2006
Lesson was taken from (with little adapatation):
Biology Lessons Part 2: Population Biology
Lesson 2.5: How Do Organisms Reproduce?
Rubric was from Rubistar
Meiosis templates were from
American Falls High School
American Falls, ID
Figure copied from Google Images http://www.accessexcellence.org/RC/VL/GG/images/meiosis.gif