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Meiosis SE 2 gizmo pdf
General Biology (BIO111)
University of California Los Angeles
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Student Exploration: Meiosis
Vocabulary: a naphase, chromosome, crossover, cytokinesis, diploid, DNA, dominant, gamete, genotype, germ cell, haploid, homologous chromosomes, interphase, meiosis, metaphase, mitosis, ovum, phenotype, prophase, recessive, sister chromatid, sperm cell, telophase, zygote
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
During mitosis , a single cell divides to produce two daughter cells. What must happen in the original cell so that each of the daughter cells has a complete set of chromosomes?
During sexual reproduction, two sex cells fuse to create a fertilized cell with a complete set of chromosomes. What must be true about the number of chromosomes in each sex cell?
Gizmo Warm-up Meiosis is a type of cell division that results in four daughter cells with half as many chromosomes as the parent cell. These daughter cells mature into gametes , or sex cells. In the Meiosis Gizmo, you will learn the steps in meiosis and experiment to produce customized sex cells and offspring.
On the STEPS tab, click Male. You are looking at a germ
cell , or a cell that will undergo meiosis to become gametes.
- Read the description of interphase at the bottom of the Gizmo. What happens to the cell at
the beginning of interphase?
Click on the DNA in the nucleus of the cell. Describe what happens.
Why is it necessary for the cell to grow and duplicate its DNA before the start of meiosis?
The original cells duplicate
The numbers of chromosomes in each sex cell
The cells grow and synthesize mRNA and proteins
The dna condenses into chromosomes
It doesn’t lose its dna and doesn’t lose size
Activity A:
Steps in meiosis
Get the Gizmo ready:
x Make sure the STEPS tab is selected. x If necessary, choose the Male cell. Click on the
DNA to copy it to proceed to prophase I.
Introduction: Unlike mitosis, which produces two identical daughter cells from one parent cell, meiosis creates four unique daughter cells with half the amount of DNA as the parent cell.
Question: How does meiosis create four daughter cells from one parent cell?
- Observe: ( Prophase I ) Click on the nucleus to break it down then click on the DNA to condense it into chromosomes. Drag the centrosomes to the top and bottom of the cell.
A. How many chromosomes does this cell have?
Each chromosome consists of a pair of sister chromatids , two identical strands of DNA that formed when DNA replicated during interphase.
B. On the image to the right, draw two lines connecting the pairs of homologous chromosomes (chromosomes of similar size with a matching set of genes).
In the Gizmo, drag the homologous chromosomes together. Click Continue.
- Observe: ( Metaphase I and Anaphase I) - Drag the groups of homologous chromosomes to the metaphase plate, then drag spindle fibers from each of the centrosomes to the chromosomes. Click the centrosome to pull the chromosomes apart.
How do the chromosomes separate in anaphase I?
- Compare: An image of the anaphase step in mitosis is shown to the right.
A. How does anaphase I in meiosis differ from anaphase
in mitosis?
B. At the end of anaphase I (meiosis), how many chromosomes are on each side?
(Activity A continued on next page)
8
They get pulled to opposite sides
Anaphase 1 in meiosis
4
Activity B:
Comparing female and male gametes
Get the Gizmo ready: x Make sure the STEPS tab is selected.
x Click Reset.
Introduction: Although both male and femal e gametes contain genetic material from the parent
organism, they perform different functions. A male gamete delivers genetic material to a female gamete. The fertilized female gamete, called a zygote , then grows into the offspring.
Question: What are the differences in meiosis between male and female cells?
- Compare: Click on the Female button. For the female cell, proceed through meiosis until you reach the end of anaphase I.
Up to this point, did you notice any differenc es between the development of male and
female gametes? Explain.
- Compare: Proceed through telophase I and cytokinesis I.
A. What do you notice about the size of the two resulting cells?
B. How does this compare to the two cells at the end of telophase I and cytokinesis I in
male cells?
- Compare: Continue through meiosis until you finish telophase II and cytokinesis II.
A. What do you notice about the four cells now?
B. What is the largest cell called?
The ovum is the largest cell in the human body. In contrast, the sperm cell is the smallest cell in the human body.
C. What are the small cells called?
Polar bodies are small cells that develop as a byproduct of meiosis in females. In humans and most other animals, these cells play no significant role and soon die.
- Think and discuss: Why do you think egg cells are large and sperm cells are small?
Male Male meiosis takes place in the testicles but female meiosis takes place in ovories
3 small 1 large
Many cells that undergo rapid meiosis
Ovum
All three of the cells are the same size
Polar bodies
An egg cell has to be able to create a new life while sperm cell just carries genetics
Activity C:
Genetic diversity
Get the Gizmo ready:
x Make sure the STEPS tab is selected. x Click Reset.
Introduction: The activities above shows that organisms can p roduce at least four different
gametes. In reality, organisms can produce millions of genetically unique gametes.
Question: How can meiosis create an unlimited number of unique gametes?
- Experiment: Use the following abbreviations for the chromosomes. Dark green – DG; Light green – LG; Dark purple – DP, Light purple – LP. Choose a Male or Female cell.
A. Proceed though meiosis to anaphase I. W hich chromosomes went up and which
went down? Up: Down:
B. Click Back and run anaphase I again a few times. Did the results ever change?
Explain.
C. Chromosomes are distributed randomly during anaphase I. What are the possible chromosome combinations in the two daughter cells? (Use DG, LG, DP, and LP.)
- Experiment: Click Reset. Choose a Male or Female cell. Proceed through meiosis until the chromosomes are condensed in Prophase I.
Drag the LG (light green) chromosome to the Allele map on the left. This shows the alleles (or variations of a gene) that are present on the chromosome. A genotype is a list of alleles. The genotype of the LG chromosome, for example, is EEFFGGHHJJ.
A. What are the genotypes of the remaining chromosomes? DG:
LP: DP:
B. After moving the centrosomes, drag the pairs of homologous chromosomes together.
Click on a chromosome. What happens?
When homologous chromosomes are paired up, they can exchange sections. This exchange of genes is called a crossover.
C. Click on several segments to creat e crossovers, and then click Continue. Proceed to anaphase I. Drag each chromosome to the Allele map and write its genotype.
LG: DG: LP: DP:
(Activity C continued on next page)
Chromosomes Anaphase
Chromosomes are distributed randoml during anaphase 1
There are 223 possible combinations
Light green
Dark green Light purple
It creates a crossover
Dg
Lp Do Lp
Activity D:
Crossover challenge
Get the Gizmo ready: x Select the EXPERIMENTATION tab. x Select the Free explore radio button.
Introduction: Earlier, you learned how crossovers can result in genetically diverse gametes. In this activity, you will perform crossovers in parent cells undergoing meiosis and combine the resulting gametes to produce offspring with specific genotypes.
Question: How can offspring be created that have a specific phenotype and genotype?
- Explore: The EXPERIMENTATION tab shows a simplified fruit fly genome, with a single pair of homologous chromosomes. Each chromosome has genes that control wing shape, body color, antenna type, and eye color. The uppercase alleles are dominant and the lower case alleles are recessive. The allele key is given at lower left. (Note that real fruit flies have eight chromosomes and many more genes.)
A. Click Reset. Without creating any crossovers, click Divide into gametes. What are
the possible genotypes of the gametes?
B. Drag a gamete from each parent into the box below to create a zygote. What are the
different combinations of possible offspring genotypes?
C. Click Show phenotype for each combination. What are the resulting phenotypes?
- Experiment: Click Reset. You can create crossovers by clicking on the middle chromatids in each of the parent cells.
A. Create a gamete with the genotype C b l r. First, click on the c gene in one of the parent cells to create the crossover. Then, click Divide into gametes.
Did you create a gamete with the genotype C b l r?
B. Click Reset. Create a gamete with the genotype: c b L R. How many crossover were
needed to create this gamete?
When a crossover occurs, the entire portion of genetic material is swapped between the two homologous chromosomes, so gene C is swapped along with gene B and gene R is swapped along with gene L.
C. Click Reset. Create a c B L r gamete. How many crossovers were needed?
(Activity D continued on next page)
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BbAa Ab
Yes
Just one
Two
Activity D (continued from previous page)
- Challenge: Select the Challenge radio button. Make sure that Target offspring 1 is selected in the dropdown menu.
Target offspring 1 is a fruit fly with normal wings (cc), a black body (bb), normal antenna (ll) and red eyes (Rr). Because the offspring receives one chromatid from each parent, each chromatid should come from a different parent.
A. Using the Gizmo, create a fruit fly with the correct genotype. Explain how you did it.
B. Is there another way to get the correct phenotype, but not the correct genotype?
Explain.
- Challenge: Use the dropdown menu to switch to the next target offspring. While creating target offspring 2-5, fill out the table below.
Target offspring
Genotype of chromatid 1
Genotype of chromatid 2
Number of crossovers Parent 1
Number of crossovers Parent 2 2 3 4
5
To produc e target offspring 5, why were two crossovers needed on one chromatid arm?
5. Think and discuss: Suppose there are two homologous chromosomes. Each chromosome
contains a single mutant allele in different parts of the chromosome. How can crossovers be beneficial in this situation? (Hint: How can you create a single, mutation-free chromosome?)
I crossed over with a lowercase r
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Meiosis SE 2 gizmo pdf
Course: General Biology (BIO111)
University: University of California Los Angeles
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