Learning Objectives: Model the steps of mitosis in order to gain a better understanding of the process

Mitosis On Goodness as a Final Cause: Since goodness is that which all things desire, it is clear that that goodness implies the aspect of an end....for a thing is perfect when it can reproduce its like, as the Philosopher says. Summa Q5:A28 Introduction The steps of mitosis are straight forward. However, when comparing mitosis with meiosis, confusion tends to occur. Mitosis and Meiosis share similarities, but the end results are different. In this lab, you will follow the movement of chromosomes through mitosis in order to create duplicate daughter cells. In the next lab, you will use the same process to examine meiosis. Definitions In the Preparation Setup below, you will prepare analogs to model the different players in the mitosis drama. One bead will represent a gene and a string of beads will represent a chromosome. In actuality, chromosomes are much longer and contain many more times the number of genes. Let us examine the players and the processes: Allele Alternate forms of the same gene found at the same location on a homologous chromosome Centromere Region on the chromosome where chromatids are held together and where they attach to the spindle during cell division. One centromere holds two sister chromatids together. Chromatid One of two identical copies of chromosomes held together by a centromere, formed when a chromosome replicates itself during cell division. Also called sister chromatids Chromatin Fine, filamentous DNA found in non-dividing cells Chromosome Highly condensed structure of DNA surrounded by proteins found when cells are undergoing division to ensure that genetic information is divided equally between the two resulting daughter cells Cytokinesis Division of a cell at the end of mitosis (or meiosis) resulting in two daughter cells. Diploid Cells that have two copies of each chromosome, one from each parent (called 2n) Gene A DNA sequence on a chromosome coding for a specific protein Haploid Cells that have one copy of each chromosome (called n) Homologous Chromosomes One chromosome from each homologous pair comes from mother (maternal chromosome) and one comes from father (paternal chromosome). They are similar but not identical each have genes in same order but alleles for each trait may differ. Tetrad Four homologous chromosomes made up of two sister chromatids and formed during the prophase of meiosis Learning Objectives: Model the steps of mitosis in order to gain a better understanding of the process Materials Required: From Biology Kit Chenille Stems (pipe cleaners) (4 lengths) Beads, Color 1 (10) Beads, Color 2 (10) Student Supplied 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 1

Safety Beads are a choking hazard. Keep away from small children. Do not put in mouth. Preparation 1. Build Paternal Chromosomes: You will need a total of 10 beads of the one color Use the diagram to the right to guide your construction Chromosome 1: Place 2 beads on a pipe cleaner Tie a knot in the pipe cleaner to model the centromere Place 1 remaining bead on the end Secure both ends so the beads do not fall off Duplicate this so that you have 2 Paternal copies of Chromosome 1 See figure to the right Chromosome 2: Place 1 bead on a pipe cleaner Tie a knot in the pipe cleaner to model the centromere Place 1 remaining bead on the end Secure both ends so the beads do not fall off Duplicate this chromatid so that you have 2 Paternal copies of Chromosome 2 See figure to the right 2. Build Maternal Chromosomes: You will need a total of 10 beads of a different color Use the diagram above to guide your construction Chromosome 1: Using 3 beads of a different color, construct Maternal Chromosome 1 Duplicate this so that you have 2 Maternal copies of Chromosome 1 Chromosome 2: Using 2 beads of the maternal color, construct Maternal Chromosome 2 Duplicate this so that you have 2 Maternal copies of Chromosome 2 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 2

3. Let us review what you have: Sometime during Interphase, S-phase will occur, in which each chromosome will duplicate The cell will have copies of each chromosome Using our organism today as an example, we have: Duplicate copies (or sister chromatids) of Chromosome 1 derived from this organism s mother Sister chromatids of Chromosome 1 derived from this organism s father These are called Homologous Pairs Genes at equivalent points on the maternal gene and the paternal gene are called homologous genes or alleles The figures below show two sets of homologous pairs of chromosomes Experiment Use your text and notes to review the important processes at each stage of mitosis. 1. Locate the cell diagrams directly following this Experiment. Notice that diagrams indicate cells with an intact nucleus, no nuclear envelope, and undergoing cytokinesis Copy these as needed and use these to diagram each stage of mitosis 2. Using the bead chromosomes : Model each of the stages: Interphase Prophase Metaphase Anaphase Telophase Cytokinesis 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 3

3. As you model each stage, use Table 1 to note your findings, especially: Major activities that occur in each step The correct number of chromosomes present in the cell for each phase The notable appearance or disappearance of structures such as: Centromeres Chromatin Sister chromatids Spindles and spindle fibers Centrioles Metaphase plate Nuclear envelope Cleavage furrow Other structures that appear or disappear, centromeres, sister chromatids, chromatin List the major activities that occur in each step in Table 1 4. Perform Data Analyses and Conclusions 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 4

Following are cell outlines. You may wish to use these to lay your chromosome models in. Or, if you wish, you can use these to as models to draw your own. 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 5

Lab Report for: Table 1 Mitosis Stage Major Events Notably Present or Absent Interphase Prophase Metaphase Anaphase Telophase Cytokinesis 1. What is the purpose of mitosis? 2. How many chromosomes did the parent cell contain in this experiment? 3. How many chromosomes did each of the daughter cells contain? 4. What is the diploid number (2n) for the organism that contains this cell? 5. What do you think would be the effect if Metaphase was skipped and the cell went from Prophase to Anaphase? 6. What would be the effect if, during Anaphase of Mitosis, the sister chromatids did not split equally? 7. Review the figure below. Does Figure A, Figure B, or both Figure A and B describe an allele. Explain your answer. 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 8