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

Goals:

a. Students will understand the process of meiosis in the genetic variation of

a population.

b. Students will understand that meiosis takes place in specialized cells in the

reproductive structures

Objectives:

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

Background Knowledge:

a. Students will have an understanding of mitosis and the process of mitosis in

cell division.

b. Students will be acquainted with the terms DNA, genes, chromosomes and

chromotids.

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 doesn’t 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 isn’t meiosis like mitosis?

We are sure that more questions will arise as the lesson proceeds.

Vocabulary:

Diploid cell

Haploid cell

Gamete cell

Homologous chromosome

Chromotid

Meiosis

Somatic cells

Tetrads

Genome

Materials:

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

-Markers

Day one:

Motivational questions:

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 Krogh’s Biology CD-Rom

Introduction:

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.

Procedure:

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.

Thought:

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
	Fur Color	Fur Type
Green Chromosome	G (green fur)	c (straight fur)
Yellow Chromosome	g (yellow Fur)	C (curly fur)
	Genes on PAIR 2	Genes on PAIR 2
	Eye color	Eyelash Length
Blue Chromosome	B (blue eyes)	L (long eyelashes)
Red Chromosome	b (red eyes)	l (short eyelashes)

Remember that we are looking at two pairs of alleles on two genes

5. Interphase

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

together.

Question: How many chromatids are present in the nucleus after DNA replication? How

many chromosomes?

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.

Conclusion/Wrap-Up

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.

Assessment

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.

Rubric

The following is the rubric to be used in the assessment.

Rubric ID: 1250162

Scientific Drawings : Meiosis Flip Book

CATEGORY	5	4	3	2	1
Phases and Stages	All phases have stages that at lease 3 stages. 50-40 points	One or more of the phases is missing a stage so that the book does not flip cohesively 39-30 points	There are few stages for each of the phases of Meiosis 29-20 points	There are phases missing or not stages are present 19-10 points	There are not stages and phases are missing 9-0 points
Correct Depiction of Phases	All the phases are drawn correctly. 30-25 points	A few of the phases are drawn incorrectly or ther is missing parts. 25-20 points	There are moderate mistakes in the depictions of the phases and stages 19-15 points	There are big mistakes in the drawing or sequencing of the phases or stages 14-10 points	One or more phases is missing from the flip book. 9-0 points
Color and Labeling	All the drawings are colored and labeled correctly 20-15 points	There are mistakes in labeling or not all the drawings are colored in the same colors. 14-10 points	There are major mistakes in labeling. Not all drawings are colored in the flipbook. 9-5 points	Theres is little color on the drawings or inconsistant colors used. Liitle or no labeling on the drawings 5-1 points	There is no color or labels on the drawing in the flipbook. 0 points