Experiment 1: Following Chromosomal DNA Movement through Meiosis

Your Full Name:

Biology 102/103

Lab 5: Meiosis

INSTRUCTIONS:

· On your own and without assistance, complete thisLab 5Answer Sheet electronically and submit it via theAssignments Folder by the date listed in theCourse Schedule (underSyllabus).

· To conduct your laboratory exercises, use the Laboratory Manual located under Course Content. Read the introduction and the directions for each exercise/experiment carefully before completing the exercises/experiments and answering the questions.

· Save your Lab 5 Answer Sheet in the following format: LastName_Lab5 (e.g., Smith_Lab5).

· You should submit your document as a Word (.doc or .docx) or Rich Text Format (.rtf) file for best compatibility.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pre-Lab Questions

1. Compare and contrast mitosis and meiosis.

 

Both mitosis and meiosis are involved with the dividing of cells and the splitting of DNA between the new cells that are made. They can also be parts of reproduction. In meiosis I, tetrad form and crossing over occurs during prophase I. This does not occur during mitosis. In metaphase I of meiosis, tetrads align at the spindle equator. The paired chromosomes have a total of four chromatids each. In mitosis, dyads align at the spindle equator. During meiosis two nuclear divisions are required but in mitosis only one nuclear division required.

Mitosis is the process, in the cell cycle, by which the chromosomes in the cell nucleus are separated into two identical sets of chromosomes. Mitosis immediately followed by cytokinesis resulting in two daughter cellscrating two diploid cells that are genetically the same to each other and the parent crating two diploid cells.

Meiosis produces four daughter divisions and four daughter cells which results in four haploid cells with half the chromosome number as the parent cell. During meiosis there is crossing over of the DNA which means that the DNA on

two different chromosomes can mix to create genetic diversity. This is why the daughter cells are genetically not the same to each other and to the parent.

 

2. What major event occurs during interphase?

 

During interphase, the cell duplicates it DNA. The cell does most of its growing in this stage. This phase also produces the components needed for cell division. Interphase consists of three phases: one synthesis phase and two gap phases. During early interphase the G1 (gap) stage growth occurs and in the late interphase (the G2 stage). DNA replication takes place during mid-interphase the S (synthesis) stage.

 

Experiment 1: Following Chromosomal DNA Movement

through Meiosis

 

Data Tables and Post-Lab Assessment

Trial 1 - Meiotic Division Beads Diagram:

Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase II

Metaphase II

Anaphase II

Telophase I

Cytokinesis

Trial 2 - Meiotic Division Beads Diagram:

Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase II

Metaphase II

Anaphase II

Telophase I

Cytokinesis

 

 

 

 

 

Post-Lab Questions

1. Poloidy of the DNA at What is the the end of meiosis I? What about at the end of meiosis II?

Meiosis I is the reductional division because it halves the number of chromosome sets per cell - a reduction from two sets (the diploid state) to one set (the haploid state). The sister chromatids then separate during the second meiotic division, meiosis II, producing haploid daughter cells.

 

2. How are meiosis I and meiosis II different?

At the end of meiosis I, both of the resulting daughter cells are haploid (definitely not diploid). However, the chromosomes are still double-stranded. The homologous pairs have already been separated. In humans, this means that the original cell had 23 pairs of chromosomes, and the cells at the end of meiosis I have 23 chromosomes (not pairs), each of which still have two sister chromatids. At the end of meiosis II, there are a total of four daughter cells, each of which is diploid. At this point, the sister chromatids have separated from each other. In humans, this means that these gametes each have 23 chromosomes, each of which has one chromatid.

 

3. Why do you use non-sister chromatids to demonstrate crossing over?

Crossing over occurs between homologous chromosomes, which are not identical, as one member of each pair of homologous chromosomes comes from the mother, and one member comes from the father. Sister chromatids are identical and crossing over would have no effect.

 

4. What combinations of alleles could result from a crossover between BD and bd chromosomes?

 

 

5. How many chromosomes were present when meiosis I started?

There are 46 chromosomes at the beginning of meiosis I.

 

6. How many nuclei are present at the end of meiosis II? How many chromosomes are in each?

There are 4 nuclei and there are 2 chromosomes in each.

 

7. Identify two ways that meiosis contributes to genetic recombination.

 

 

 

Crossing over during prophase I, corresponding segments of non-sister chromatids are exchanged and independent assortment of homologous chromosomes.

8. Why is it necessary to reduce the number of chromosomes in gametes, but not in other cells?

Gametes have fewer chromosomes then other cells so that the offspring has the same amount of chromosomes as the parents

9. Blue whales have 44 chromosomes in every cell. Determine how many chromosomes you would expect to find in the following:

 

 

 

i. Sperm Cell: 22

 

i. Egg Cell: 22

 

iii. Daughter Cell from Mitosis: 44

 

iv. Daughter Cell from Meiosis II: 22

 

10. Research and find a disease that is caused by chromosomal mutations. When does the mutation occur? What chromosomes are affected? What are the consequences?

The human body has 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes. This gives humans 46 chromosomes in total. Chromosomal genetic disorders occur when chromosomes are partially or completely missing, altered or duplicated. An example of a chromosomal genetic disorder is Down syndrome. Down syndrome is the result of an extra, third copy of chromosome 21 being present in a person. This extra chromosome results in extra protein production and upsets the body’s balanced systems. During pregnancy chromosomal abnormalities can cause the death of an embryo or fetus. Chromosomal disorders can result in mental retardation or other developmental problems. Older pregnant women have a higher risk of passing on chromosomal genetic disorders.
 

11. Diagram what would happen if sexual reproduction took place for four generations using diploid (2n) cells.

Experiment 2: The Importance of Cell Cycle Control

Data Tables and Post-Lab Assessment

1.

 

2.

 

3.

 

4.

 

5.

 

Post-Lab Questions

1. Record your hypothesis from Step 1 in the Procedure section here.

I might observe if all the chromosomes are normal except for one added chromosomes then there will be an abnormality in the cell and it will shape different from the rest.
 

2. What do your results indicate about cell cycle control?

 

3. Suppose a person developed a mutation in a somatic cell which diminishes the performance of the body’s natural cell cycle control proteins. This mutation resulted in cancer, but was effectively treated with a cocktail of cancer-fighting techniques. Is it possible for this person’s future children to inherit this cancer-causing mutation? Be specific when you explain why or why not.

 

4. Why do cells which lack cell cycle control exhibit karyotypes which look physically different than cells with normal cell cycle.

 

5. What are HeLa cells? Why are HeLa cells appropriate for this experiment?