MITOSIS AND MEIOSIS PROJECT LAB REPORT

MITOSISAND MEIOSIS PROJECT LAB REPORT

Mitosisand MEiosis

LabFormat:This lab is a remote lab activity.

Relationshipto Theory:In this lab you will be examining the underlying processes that makeup the cell cycle.

Instructionsfor Instructors:This protocol is written under an open source CC BY license. You mayuse the procedure as is or modify as necessary for your class. Besure to let your students know if they should complete optionalexercises in this lab procedure as lab technicians will not know ifyou want your students to complete optional exercise.

RemoteResources:Primary – Microscope, Secondary – Mitosis and Meiosis slide set.

Instructionsfor Students:Read the complete laboratory procedure before coming to lab. Underthe experimental sections, complete all pre-lab materials beforelogging on to the remote lab, complete data collection sectionsduring your on-line period, and answer questions in analysis sectionsafter your on-line period. Your instructor will let you know if youare required to complete any optional exercises in this lab.

Contents

Mitosisand MEiosis 1

LearningObjectives 2

BackgroundInformation 2

Equipment 6

Preparingto Use the Remote Web-based Science Lab (RWSL) 7

Introductionto the Remote Equipment and Control Panel 7

Pre-LabQuestions 7

ExperimentalProcedure: 10

Exercise1: Mitosis in Animal and Plant Cells 10

Exercise2: Calculate the Percentage of Time Spent in Each Stage of Mitosis 11

Exercise3: Growth in the Onion Root 12

Exercise4: Stages of Meiosis 13

Exercise5: Meiosis in Humans (Optional) 13

Questions: Mitosis and Meiosis Experiment 14

AppendixA – Introduction to the RWSL Microscope 15

AppendixB – Loading Slides 16

AppendixC – Microscope Control 17

AppendixD – Manipulating the Microscope Image 18

AppendixE – Capturing and Saving a Microscope Image 20

AppendixF – Camera Controls 21

LearningObjectives

Aftercompleting this laboratory experiment, you should be able to do thefollowing things:

  • Describe the cell cycle.

  • Identify the stages of mitosis from prepared slides.

  • Calculate the percentage of time a cell spends in each stage of the cell cycle.

  • Quantify the relationship between cell division and cell growth.

  • Recognize the processes of meiosis and how it differs from mitosis.

  • Identify support cells from human spermatogenesis and oogenesis. (Optional)

BackgroundInformation

IfI asked you “Where do cells come from?” what would you answer? Inmodern biology our understanding of a the cell as the basic buildingblock of life is codified in a set of principles called the CellTheory which was first codified by Schleiden and Schwann in 1838-39. The cell theory is second only to the theory of evolution by naturalselection in understanding the relatedness of life. Cell Theory saysthe following:

1. All living organisms are composed of one or more cells.

2.Cells are the basic building blocks of all life.

3.All cells are descended from a preexisting cell.

Whilethese may seem like relative simple points it took scientists severalcenturies to produce the cell theory.

Thedevelopment of the cell theory directly follows the development ofthe microscope. The name “cell” was coined by Robert Hooke6in 1665. While observing a piece of cork under his microscope hethought that the microscopic units that made up the cork looked likethe rooms, or “cella” in Latin, that monks lived in. This wasclosely followed by the discovery of single celled organisms byAntoni van Leeuwenhoek3-5in 1676. Leeuwenhoek discovered motile microscopic particles byexamining scrapings from his teeth under his microscope. In 1838Metthias Schleiden7and Theodor Schwann8presented evidence that all plants and animals are composed of cells.However, there were still some questions as to where cells came from,as Schleiden believed cells formed through a process ofcrystallization. This theory was simply a variant on the belief ofAristotle that life could come into existence by spontaneousgeneration.

Itwas not until the 1850s that a group of scientist was able to showthat new cells were produced from preexisting cells9.However, most scientists believe the definitive test disprovingspontaneous creation of microbial life was conducted by Louis Pasteurin 186210.In Pasteur’s experiment two flasks were each set-up with bacterialgrowing broth (a liquid that is conducive to the growth of bacteria)and sterilized. Both flasks were left open to the air but in such away that dust could enter only flask 1 not flask 2. After a period oftime bacteria growth was seen in only flask 1 and not in flask 2. This showed that dust (bacteria) had to be added to the broth inorder for bacteria to grow.

Inthis lab we will be examining the mechanism underlying the thirdprinciple of the cell theory “that all cells are descended frompreexisting cells”. There are two processes involving theproduction on new cells, the first process, mitosis, is used forgrowth and to replace old or dead cells. The second process,meiosis, is used to produce gametes (egg and sperm) cells that areused for sexual reproduction. An important point to keep in mind isthat we name the type of cell cycle based on what is happening to thenucleus and genetic material.

Themitotic cell cycle (see figure 1) is used to produce new somatic(body) cells in the organism. The mitotic cell cycle in the simplestform is composed of two parts Interstage and Mitosis. However, eachof these parts can be further divided. Mitosis can be divided intofour parts: Prostage, Metastage, Anastage, and Telostage which willbe described below. Mitosis, in fact, means the division of thenucleus to produce two identical daughter cells. The division of thecell itself is called cytokinesis and overlaps telostage but is notactually classified as part of it. Interstage (the part of thecell cycle between actual divisions) is composed of three parts Gap1(sometimes referred to as growth1) the cell grows and performs normalcellular functions, Synthesis (s stage) DNA is replicated, and Gap2(sometimes referred to as growth2) is where the cellular organellesare replicated. There is one additional stage to the cell cycle Gap0.A cell that has stopped cycling (dividing) either temporarily orpermanently has entered Gap0.

Thedifferent stages of the cell cycle were identified as morphologicalchanges by Waclaw Mayzel in 18751,2. All these morphological changes can be observed in a compoundmicroscope. During Interstage (figure 2A) there is a clearly definednuclear envelope filled with dispersed chromosomes. As the cellenters Prostage (figure 2B) the chromosomes condense and the mitoticspindle forms. At this point each chromosome is composed of twosister chromatids joined at the centromere. Additionally, thenuclear envelope breaks down and the mitotic spindle begins attachingto the chromosomes at the centromere. (In some texts the breakdown ofthe nuclear envelope and the attachment of the mitotic spindle to thechromosomes is listed as an additional stage Prometaphase). InMetaphase (figure 2C) the chromosomes line up in the middle of thecell forming a structure called the metaphase plate. During Anaphase(figure 2D) the centromere splits and each chromatid now a chromosomeis pulled to opposite sides of the cell. In the last stage Telophase(figure 2E) the chromosomes become less condensed, two new nucleiform and the mitotic spindle de polymerizes. This officially endsmitosis which as mentioned before is the replication and division ofthe nucleus. The cell cycle ends with cytokinesis, the division ofthe cytoplasm, which often overlaps late telophase.

Theother type of cell cycle is called meiosis and is used in sexualreproduction to produce gametes (sperm and egg in most animals andplants). In plants and animals each organism contains two copies ofeach chromosome this is called diploid. In order for sexualreproduction to occur properly the number of chromosomes need to bereduced by half which is called haploid. If the chromosome numberwas not reduced by half then each new generation would have twice thenumber of chromosomes as the previous organism which is calledpolyploidy. In many organisms a state of polyploidy causesbiological defects.

Mechanisticallymeiosis differs from mitosis in that two rounds of cell divisionoccur, referred to as meiosis I and meiosis II, with only one roundof DNA synthesis. Figure #3 shows the stages of meiosis were thereare differences between the corresponding mitotic and meiotic stages. This produces 4 haploid cells the number of mature gametes variesdepending on whether the final mature cell is a sperm cell or eggcell (Figure 3). In meiosis I S stage occurs as normal. The firstdifference between mitosis and meiosis I occurs in Prophase I, duringProphase I the homologous chromosomes pair up and exchange geneticmaterial by crossover (Figure 3). This exchange of genetic materialincreases the genetic variation in the offspring. The nextdifference occurs in anaphaseI, during anaphase I instead of the centromere dividing it staysconnected and the homologous chromosomes are segregated to theopposite poles (Figure 3). During Cytokinesis I we see the firstdifference between spermatogenesis (sperm formation) and oogenesis(egg formation). During cytokinesis of the egg the cytoplasm dividesunequally with one of the daughter cells getting most of thecytoplasm, the smaller cell is called a polar body (Figure 3B). Thepresperm cells undergo an equal cytokinesis (Figure 3A). The cellswill then enter a second cell cycle, meiosis II, without replicatingDNA. The length of interphase between meiosis I and meiosis IIvaries from nonexistent too years depending on the organism. Inmeiosis II during Anaphase II the kinetochore divides and the sisterchromatids are pulled to opposite poles of the cell. Again the inoogenesis the cell undergoes unequal cytokinesis producing an oogoniaand another polar body, while the sperm cells divide equally. Thisproduces four haploid spermatocytes in the male line and one haploidoogonia and 2 or 3 haploid polar bodies in the female line. Thespermatocytes and oogonia go on to mature in to sperm and egg cells,which will give rise to a new generation.

Nowthat we have and understanding of the mechanisms of mitosis andmeiosis it is clear how each separately links to the third principleof the cell theory: all cells descend from preexisting cells. Forinstance we know that new somatic cells arise from mitosis, when anolder cell divides. Additionally, we know that the development of anew multi cellular organism starts with the fusion of two gametes(fertilization) which produces a zygote. The remaining questionthough is how does mitosis and meiosis relate to each other. Theanswer to this question depends on whether we are talking about amulti cellular animal or plant. In multicellar animals the zygotedivides a few times mitotically then the cells are separated into twopopulations one population will continue to divide mitotically andwill go on to form all the somatic cells. The second population willform the germline (Figure 4A). In plants the first few stages arethe same, the difference occurs in that a population of cells is notset aside to form a germline (Figure 4B). Instead germline cells arerecruited from the somatic cells when they are needed.

References:

Medycyna,czasopismo tygodniowe dla lekarzy (1875 3(45), 409/0412)

Centralblattf. die Med. Wissenschaften (1875 50: 849–852)

Dobell,C. Antony van Leeuwenhoek and His “Little Animals” (Dover, NewYork, 1960).

Wolpert,L. Curr. Biol. 6, 225–228 (1995).

Singer,S. A Short History of Biology (Clarendon, Oxford, 1931).

Westfall,R. S. Hooke, Robert in Dictionary of Scientific Biography Vol. 7 (ed.Gillespie, C.) 481–488 (Scribner, New York, 1980).

Schleiden,M. J. Arch. Anat. Physiol. Wiss. Med. 13, 137–176 (1838).

Schwann,T. Mikroskopische Untersuchungen über die Übereinstimmung in derStruktur und dem Wachstum der Tiere und Pflanzen (Sander’schenBuchhandlung, Berlin, 1839).

Mayr,E. The Growth of the Biological Thought (Belknap, Cambridge, MA,1982).

Pasteur,L. A. Ann. Sci. Nat. (part. zool.) 16, 5–98 (1861).

Equipment

  • Paper

  • Pencil/pen

  • Slides

  • Onion Root Tip

  • Whitefish Blastula

  • Mammal Graafian Follicles

  • Human Testis

  • Ascaris lumbricoides

  • Grasshopper Testis

  • Computer with Internet access (for the remote laboratory and for data analysis)

Preparingto Use the Remote Web-based Science Lab (RWSL)

Clickon this link to access the Installguide for the RWSL: http://denverlabinfo.nanslo.org

Followall the directions on this webpage to get your computer ready forconnecting to the remote lab.

Introductionto the Remote Equipment and Control Panel

Watchthis short tutorial video to see how to use the RWSL control panel:http://denverlabinfo.nanslo.org/video/microscope.html

Thereare appendices at the end of this document that you can refer toduring your lab if you need to remind yourself how to accomplish someof the tasks using the RWSL control panel.

Pre-LabQuestions

Pre-lab1:

Newcells are produced in animals and plants by the division of oldcells. These new cells can be used for growth or to replace dead ordamaged cells. As stated in the introduction, the cell cycle isdivided into two parts the replication and division of the geneticmaterial (mitosis) and the division of the cytoplasm (cytokinesis). In this experiment you will use prepared slides of an onion root tipand a whitefish blastula to identify the stages of mitosis.

Theonion root tip is divided into four sections based on the behaviorand function of the cells (Figure 5). The first region is the rootcap which protects the growing root. The second is the meristeam, aregion of highly mitotically active cells. Then there are theelongation regions where cells are growing, and then lastly thematuration region where cells become fully mature root cells. Whilethe onion root tip is divided into four cell population (root cap,meristeam, elongation and maturation) at the developmental stage ofdevelopment you are looking at, the cells in the white fish blastulaare a uniform population.

Pre-lab1 Questions:

  • Do you think you will see any differences between plant or animal cells? What differences do you think you will see?

Yes.There would be differences between plant and animal cells. In aninstance, I expect to find plant cells bigger than the animal cells.Plant cells would have chloroplast, which animal cells lack. Plantcells are expected to have cell walls while animal cells lack cellwalls. Plant cells have centrosome, which animal cells lack. Plantcells are expected to have larger central vacuole than the animalcells. Animal cells would have more lysosomes than the plant cellsand at the same time, plant cells are expected to have plasticideswhich animal cells lack.

  • Rewrite your answer to question one in the form of an If … Then … hypotheses.

Ifa cell has chloroplast, cell wall, centrosome, large central vacuoleand few lysosomes, then it is a plant cell.

Pre-Lab2:

Atthe time when the whitefish blastula slide was prepared, the cellswere arrested at their current stage within the cell cycle byfixation, which is a chemical reaction that stops the biologicalprocess in the cell. Fixation also preserves the tissues byimmobilizes the cells, organelles, and proteins through chemicalcross linking. The duration of each stage of the cell cycle in theblastula can be estimated by determining the proportion of cellsarrested at each stage of mitosis with respect to the number of cellsin interstage.

Let’sassume that you examined a slide and determined the stage at which100 cells were arrested by fixation. It is known that whitefishblastula cells take about 24 hours to complete the cell cycle. Bydetermining the percentage of cells in each stage of mitosis and inInterstage, you can calculate the amount of time spent in each stage.For example, if ten cells out of 100 were found to be in Prostage,the percentage of cells is 10/100 x 100 = 10%. This shows that anyone of the hypothetical cells spends 10% of the time in Prostage, sothey spend 0.10 x 24 hours or 2.4 hr (2 hr and 24 min) in that stage.

Pre-lab2 Questions:

  • Create a table to record your data. [Insert it below]

Cell cycle stage

Number of cells arrested by fixation.

Interphase

170

Prophase

20

Metaphase

15

Anaphase

6

Telophase

5

Pre-Lab3:

Inthis exercise we are going to study the growth of the onion root. Growth can be effected by both the number of cells and the size ofthe cells. You will look at four areas of the onion root the tip,one each in: the cap cells, the meristeam, the elongation region, andthe maturations region. In each region you will determine the lengthof the cells and the percentage of cells that are in any stagemitosis (often called the mitotic index).

Pre-lab3 Questions:

  • Based on your knowledge of the cell cycle, what kind of relationship do you think you will see between cell size and the mitotic index?

Mitoticindex is the measure of a cell proliferation status. It is the ratiobetween the number of cells in mitosis and the total number of cells.A relationship would exist between the cell population and mitoticindex in a nature that the higher the cell population the lower themitotic index.

  • Using the If … Then … format, rewrite your answer to question on in the form of a hypothesis.

Ifan organism is found to have a high number of cell populations atdistinct fixation stages, then the organism has a low mitotic index.

  • Create a table to record your data. [insert the data table below]

Onion root tip regions

Length in interphase

Cap cells

4mm

The meristem

100mm

The elongation region

200mm

Maturation region

150mm

Pre-Lab4:

Observingthe different stages of meiosis is often difficult do to thestructure of the organs in which meiosis and fertilization occur. One way scientist gets around this type of problem is through the useof model organisms. A model organism is an organism in which aparticular biological process is easily observed or manipulated. Twoexamples of model organisms used in the study of meiosis are thegrasshopper testis and the Ascarislumbricoidesovary. The reason that these are good model organisms for theprocess of meiosis is that meiotic cells travel down the organ in aliner path. Later stages of meiosis are farther along in the organthan earlier. For example in a grasshopper testis it is oftenpossible to observe all stages of both meiosis I and meiosis II. Theovary of the Ascarislumbricoides (anematode worm) is similarly arranged. However, in the case of theAscarislumbricoides ovaryyou can see the polar bodies produced during oogenesis as their lifetime is long enough that they are preserved in the fixed tissue. Additionally, fertilization also occurs in the ovary allowing for theobservation of the pronuclei in early fertilization. In this lab weare going to use these two model organisms to observe the processesof meiosis and fertilization.

Pre-lab4 Questions:

  • Why are we not using human ovaries and testis to observe meiosis and pronuclei?

Inthe human ovary and testicles, meiotic division does not travel downthe organ in a linear path. In this instance, the later stages ofmeiosis are not clearly visible and tend to intermingle with theearly stages of meiosis. In the human ovary and testis therefore, itis impossible to clearly observe all the stages of both meiosis I andmeiosis II. In this instance, the use of model organism is advisableto observe the meiotic stage hence the testicles of a grasshopper orthe ovaries of Ascaris lumbricoides are applicable.

Inthe model organisms, additional fertilization occurs in the ovaryallowing for the observation of pronuclear in the earlyfertilization. This process is difficult to observe when a humanovary is used.

Pre-Lab5:

Inhumans meiosis occurs in special tissues in specialized organs, theovary in females and the testes in males. The biological function ofthese organs is to isolate, protect, support, and deliver thegametes. Early in the process of development the cells that willbecome the gametes temporally exit the cell cycle and are segregatedto a region of the embryo that will become the testes or ovaries.This process of segregation helps protect the DNA of germline cellsfrom damage in two ways. The first is that these cells will undergofewer rounds of division and therefore DNA synthesis then the othercells in the body. This is important because DNA synthesis is one ofthe most common ways DNA modification can occur. Second these cellslive inside the structure of the testes or ovary and get someprotection from the outside world. In this exercise we will observethe cells needed to support the development of the sperm and eggs inhumans in this exercise. In addition to identifying fully developedsperm and eggs.

Pre-lab5 Questions:

  • Do you think the appearance of the chromosomes will look any different in the meiotic cell cycle stages then in the mitotic cell cycle stages you observed earlier, explain

Theappearance of the chromosomes would be different between meiosis Istage of cell division from the appearance of a chromosome in mitoticdivision. This is because chromosomes do not divide in meiosis I butdivide in mitotic stage. However, there would be no appearancedifferences between chromosome appearance in meiotic II stage andmitotic stage of cell cycle.

ExperimentalProcedure:

Onceyou have logged on to the microscope you will perform the followingLaboratory procedures:

Exercise1: Mitosis in Animal and Plant Cells

DataCollection:

  • Select the prepared slide of the whitefish blastula (Slide Cassette 1: #7) using the RWSL microscope controls.

  • Locate the blastula then carefully work your way through all the objectives, focusing with each one, until you reach the 40X or 60X objective and working as a group identify a cell in each stage of mitosis. Use the “capture image” feature on the RWSL microscope control panel to capture an image of each stage. (Each member of your group should use the microscope to identify at least one stage.)

  • Select the prepared slide of the onion root tip (Slide Cassette 1: #8) using the RWSL microscope controls.

  • Locate the onion root tip then carefully work your way through all the objectives, focusing with each one, until you reach the 40X or 60X objective and working as a group identify the stages of mitosis. Use the “capture image” feature on the RWSL control panel to capture an image of each stage. (Each member of your group should use the microscope to identify at least one stage.)

Analysis:

  • Use the images from question 4 and the insert and textbox feature on your computer’s word processing program. Label the plasma membrane, chromosomes, mitotic spindle, nuclear membrane, and centriole, for each blastula mitotic stage image as appropriate. [Place your images below.]

Firstpicture, onion cell cycle at interphase.

Plasmasmembrane Nucleus Nucleic envelop

  • Use the images from question 6 and the insert and textbox feature on your computer word processing program. Label the plasma membrane, chromosomes, mitotic spindle, nuclear membrane, and centriole, for each onion root tip mitotic stage image as appropriate. [Place your images below.]

  • Think back to the pre-lab questions about differences in plant and animal cell mitosis. Were you prediction correct? What, if any, differences did you actual see?

Thepredictions turned out to be incorrect for there is no differentbetween a plant and an animal cell in mitosis.

  • If your predictions were incorrect revise your hypotheses based on your new understanding of the differences between mitosis in plants and animals.

Ifa cell is undergoing mitosis either in plants or animals, the cellswould tend to be more similar.

Exercise2: Calculate the Percentage of Time Spent in Each Stage of Mitosis

DataCollections:

  • Select the whitefish blastula slide (Slide Cassette 1: #7) select an area of a blastula so that your entire field of view is filled with cells.

  • Count and record the number of cells in each stage of the cell cycle in your field of view. Enter this information in the table you created in the pre-lab(insert it below). (Each group member should count at least one field of view.)

  • Repeat the step 3 three times with a new field of view each time.

Analysis:

  • Calculate the percentage of time the cells spent in each stage of the cell cycle for each field of view independently. Create a new table to hold this information (insert it below).

Lengtheof time at interphase = 20/170 ×100 = 11.76%

=0.1176×24=2.822 hours.

Prophase5/20 × 100 =25%

=0.25 × 24 = 6 hours.

Metaphase (15 -6)/15 × 100 = 60 %

=o.6 × 24 = 14.4 hours

Anaphase(6-5)/6 × 100 = 16.7%

=0.167×24 =4 hours

Telophase0/5×100=0%

=Insignificant hours

  • Now sum the numbers from all four data sets and use the totals to calculate the percentage of time the cells spent in each stage of the cell cycle. Place this data in the same table as the data from question 5. [Insert Table Below]

Totaltime spent = ( 2.82 + 6 + 14.4 + 4) = 27.22

Percentagetime spent = time spent at a stage / total time × 100%

Interphase=10.36%

Meterphase=22.04%

Anaphase=52.90%

Telophase= insignificant %

  • Compare the time the cells spent in each stage of the cell cycle from the summed data to that from the individual data do you notice any differences?

Thecell spends more time in the anaphase stage of cell division andultimately spends insignificantly shorter time in the telophasestage.

Animportant part of validating data is determining how repeatable thedata are. A simple way to examine repeatability is to look at thevariability of the data. One way to calculate this variability is byusing a standard deviation calculation. The equation to calculatestandard deviation is . This equation is actually quite simple inthis case: n is the number of samples (number of fields of views youcounted), xiis one of the numbers in your data set (one field of view), μ is theaverage of the numbers in the data set (average of all field ofviews), and Σ means you sum the numbers. As an example, suppose wehad four numbers 1.0, 2.0, 3.0, &amp 4.0 the average of thesenumbers is 2.5 therefore the standard deviation of this set is.

  • In the above example of a standard deviation calculation, your calculator would have displayed the result as 1.11803398… Why did we only display 1.1 as the answer?

Workingwith the calculation at one significant figure would make it easy andstandard for all the operations. This would make comparison easier.

  • Calculate the standard deviation for each of your cell stages. List the length of time each cell spends in each stage of the cell cycle with its standard deviation below, in this format: time in stage +/- standard deviation.

Standarddeviation

Exercise3: Growth in the Onion Root

DataCollection:

  • Select the onion root tip slide (Slide Cassette 1: 8) using the RWSL microscope control. (Each member of the group should collect data from a region)

  • Position the microscope so that you are looking at the cap cells (See figure #5: Onion Root Tip for a refresher).

  • Count all the cells in the field of view count how many of them are in mitosis.

  • Determine how long each cell is.

  • Position your sample so that you are looking at the meristeam and repeat steps 4&amp5

  • Position your sample so that you are looking at the elongation region and repeat steps 4&amp5

  • Position your sample so that you are looking at the maturation region and repeat steps 4&amp5

Analysis:

  • Calculate the mitotic index for each region. Modify your table from question one and enter the mitotic index your new table.

Mitoticindex = total number of cells with visible chromosomes ÷ totalnumber of cells.

Mitoticindex for:-

  1. Cell cup

90 ÷ 12 = 7.5

  1. Meristem region

100 ÷ 15 = 6.67

  1. Elongation region

150 ÷ 10 = 15

  1. Marturation region

200 ÷ 40 = 5

  • Calculate the size of the cells for each region and record that in your table from question 11. The total field of view for you microscope is 305µm at 40X and 205µm at 60X.[Insert your data table below]

Onion root tip regions

Length in interphase

Number of cells with visible chromosomes

Total number of cells

Mitotic index

Cap cells

4 mm

12

90

7.5

The meristem

100mm

15

100

6.67

The elongation region

200mm

10

150

15

Maturation region

150mm

40

200

5

  • How does your prediction of the relationship of the mitotic index to cell size correlate to the data you collected?

Theprediction between mitotic index and to the cell size has a positivecorrelation, were there is more growth like in the region of cellelongation, the mitotic index is high and in the regions of law celldivision like in the maturation region, the mitotic index is law.

  • If needed rewrite your hypothesis in light of the new data you collected.

  • Based on your observations and pre0lab reading what stage of the cell cycle are the onion root cells in the elongation region likely in?

Theonion root cells are in the G-1 (growth 1) stage of the interphasethat is characterized by rapid cell growth and cell division beforethe actual cell cycle.

Exercise4: Stages of Meiosis

DataCollection:

  • Select the grasshopper testis slide (Slide Cassette 1: #12) using the RWSL microscope control panel.

  • Use the “capture image” feature on the RWSL control panel to capture an image of the testis.

  • Select the Ascaris lumbricoides Female slide (Slide Cassette 1: #11) using the RWSL microscope control panel.

  • Use the “capture image” feature on the RWSL control panel to capture an image of a developing oocyte with a polar body attached.

  • Use the “capture image” feature on the RWSL control panel to capture an image of a fertilized egg with an egg and sperm pronuclei.

Analysis:

  • Use the insert and textbox feature on your computer word processing program to label two cells in meiosis I and two cells in meiosis II. [Place your image below.

MeioticI division

Spermcell.

Cellabove in meiotic II division.

  • Use the insert and textbox feature on your computer word processing program to label the oocyte, polar bodies, and egg and sperm pronuclei as appropriate in the two Ascaris lumbricoides pictures. [Place your image below]

Cellbelow in meiotic II division.

Primaryoocyte Secondary oocyte

cellin meiotic I division.

Exercise5: Meiosis in Humans (Optional)

DataCollection:

  • Select the prepared slide of the Mammal Graafian Follicles (Slide Cassette 1: #9) using the RWSL microscope control.

  • Use the “capture image” feature on the RWSL microscope control panel to capture an image of the Mammal Graafin Follicles.

  • Select the prepared slide of the Human Testis (Slide Cassette 1: #8) using the RWSL microscope control.

  • Use the “capture image” feature on the RWSL microscope control panel to capture an image of the Human Testes.

Analysis

  • Use the insert and textbox feature on your computer word processing program to label the primary follicle, primary oocyte, secondary follicle and secondary oocyte. [include it below]

  • Use the insert and textbox feature on your computer word processing program to label seminiferous tubules and mature tailed sperm. [include image below]

  • Was your prediction in question one correct, explain.

Questions: Mitosis and Meiosis Experiment

  • Which is more similar to mitosis: meiosis I or meiosis II? Explain your answer.

MeiosisII is more similar to mitosis since in the anaphase of the mitoticcell division the chromosomes do not dis integrate. It thereforemeans that the resultant effect of meiotic II cell stage results tothe formation of two daughter cells that is a common characteristicwith mitotic division. Meiotic I division results to the formation ofhaploid cells resulting to formation of four cells that lack completeresemblance from the parent cells as in the case of mitotic andmeiotic II cell division stage.

  • Can a haploid cell undergo meiosis? Can it divide by mitosis?

Haploidcells can undergo meiosis to form other two cells with the samecharacteristics. However, it cannot undergo a mitotic cell divisionsince the DNA materials cannot disintegrate to result to duplicationin mitotic process.

  • Why do you expect the diploid number of chromosomes always to be an even number and never an odd number?

Diploidchromosomes divide by duplication. It therefor means that any numberof diploid chromosomes that duplicate would result to even numberdaughter cells.

  • How does crossing over contribute to genetic variability? Does this have any evolutionary significance?

Crossingover of genetic materials results to the transmission of geneticinformation from one chromosome to another. The presentation of a newgenetic information can influence the structure and the functionalityof a cell thereby could an evolution of the cell.

Howdoes the cell decide which homologue goes to which pole duringanaphase I? How does this contribute to genetic variability?

Inanaphase, I stage of cell division, the sister chromatids are eachattached by the action of the spindle fibers on each pole of thecell. In the case of shortening of the spindle fibers, the chromatidswill be drawn to the opposite poles in relation to the fibers withwhich they are attached.

AppendixA – Introduction to the RWSL Microscope

TheRWSL microscope is a high-quality digital microscope located in theremote lab facility. You will be controlling it using a controlpanel that is designed to give you complete control over everyfunction of the microscope, just as if you were sitting in front ofit.

Youmust call into a voice conference to communicate with your labpartners and with the Lab Technicians. This is very importantbecause only one person can be in control of the equipment at any onetime, so you will need to coordinate and collaborate with your labpartners.

Youtake control of the equipment by right-clicking anywhere on thescreen and selecting Request Control. You release control byright-clicking too.

AppendixB – Loading Slides

Clickingon the Slide Loader tab at the top of the screen will display thecontrols for the Slide Loader robot. There can be up to fourcassettes available on the Slide Loader, and each cassette can holdup to 50 slides. There will be a drop-down list for each cassettethat is available. In the above example, only cassette #1 isavailable on the Slide Loader. You can click on it to select aspecific slide to be loaded, as in the image below:

Onceyou select the slide you want to load on the microscope, click theLoad button to the right of the drop-down list. You will see amessage telling you that the slide is loading. You can also watchthis happening using the picture-in-picture (PIP) camera (seeAppendix F – Camera Controls).

Noticethat when a slide is actually on the microscope (or when it is beingloaded or unloaded), the cassette controls will be grayed out so youcannot load a second slide until the first is removed.

Oncethe slide is on the microscope, it will be listed in the “CurrentSlide on Stage” box, and the only thing that the Slide Loader robotcan do is return it to the cassette when you click the “ReturnSlide to Cassette” button.

Tomove the slide around while it is on the microscope stage, you mustreturn to the Microscope tab to see those controls.

AppendixC – Microscope Control

Themicroscope stage controls are boxed in red in the above image. Theallow you to move the microscope stage (which holds the specimenslide) left, right, forward or backward. You can also focus bymoving the stage up and down.

Youcan change the objective, which gives you increased or decreasedmagnification, by clicking the buttons under Objective Selection.

TheCondenser control controls whether or not the Condenser lens is inthe light beam. You want to have the condenser OUT for the 4xobjective, but IN for all the others.

AppendixD – Manipulating the Microscope Image

Youcan manipulate the microscope image by using the controls in the redboxed area above. The White Balance should be used only if the imageappears to be brown or gray and you think you might need to adjust it(although it won’t hurt anything to click this button).

TheNormal, Negative, etc, control buttons in this area are used todisplay the image slightly differently in order to highlight certainfeatures. Here is some information from the Nikon website(http://www.microscopyu.com/articles/digitalimaging/digitalsight/correctingimages.html)about these settings and when they might be used:

Normal:&nbspInthis mode, the image is displayed in the natural color scheme that isobserved in the microscope eyepieces (Figure 3). For the majority ofimages captured with the Digital Sight system, the normal coloroutput is the most effective mode for accurate and effectivereproduction of all specimen details.

Negative:&nbspThe&nbspNegativeeffect displays a brightness- and color-inverted form of the image,where red, green, and blue values are converted into theircomplementary colors (Figure 4). The technique is useful withspecimens for which color inversion can be of benefit in exposingsubtle details, or in quantitative analysis of specimens.

BlueBlack:&nbspThismode represents the black portions of the&nbspNegative&nbspimagein blue, and is often useful to reveal details in specimens having ahigh degree of contrast. As a special effect, the&nbspBlueBlack&nbspmodecan be beneficial as a presentation tool.

Black&amp White:This mode displays a grayscale form of the image (Figure 6). It canbe effectively used for monochromatic images such as those acquiredwith differential interference contrast or phase contrast techniques.In many cases, digital images destined for publication in scientificjournals must first be converted into black &amp white renditions ofthose captured in full color. The&nbspB&amp W&nbspfiltercan often aid the microscopist in preparing images for publication ororal presentation.

Sepia:&nbspThiseffect is essentially a monochrome image version displayed in sepia(brownish) tones instead of grayscale (Figure 7). The&nbspSepia&nbspmodeis more likely to be utilized in general photographic applicationsthan in microscopy, although the effect may enhance the visibility ofspecimen detail in certain instances.

AutoExposure is normally turned on, but you can turn it off if you wantto play around with the brightness of the light source and not havethe microscope camera automatically adjust, though it’s usuallybest to leave it turned on.

Ifyou turn off the Auto Exposure, then some new controls appear thatlet you turn the LED off or on, and also adjust the intensity of thelight source. The intensity of the light source can be increased ordecreased manually with the dial that now appears next to theObjective control.

AppendixE – Capturing and Saving a Microscope Image

Youcan capture a high-resolution image of what is currently in the fieldof view of the objective by clicking the Capture Image button, whichwill turn bright green while it is capturing the image. When theCapture Image light turns off, the image has been successfullycaptured. After the image is captured, click View Captured Image tosee the high-resolution image.

Afteropening this image, you will need to take a snapshot of it and saveit to your computer. There are several ways to do this, depending onyour operating system:

Windows:

  • Pressing the two keys: ALT and Prt Scn simultaneously will copy the active window into the clipboard. Then you can paste it into a document.

  • Windows 7 and above has a Snipping Tool program under Programs/Accessories, which can capture selected areas of the screen.

Mac:Pressthree keys simultaneously: Shift 4 This will change your icon into a little cross. Now, press thespacebar and the icon becomes a camera. Click in the image windowyou want to take a snapshot of and it will be saved as a file to yourdesktop.

Thereare lots of free screenshot utilities you can also use to do this.

AppendixF – Camera Controls

Clickingthe Picture-in-Picture button will open a window that shows the viewfrom a camera placed directly in front of the microscope. The arrowbuttons allow you to swivel the camera around so you can see whateveryou want to look at in the lab. The Camera Preset Position buttonsare programmed to show you particular portions of the apparatus. Ifyou hover the mouse over them, a box will pop up that lists what eachposition will show you (see below).