Lab 12: Mitosis and Meiosis PDF Fall 2024

Lab 12: Mitosis and Meiosis Lab Manual 7.1-7.5 Fall 2024  Goals of this lab Concepts Outputs Understand the differences and similarities Used models to learn the steps of mitosis between m...

Lab 12: Mitosis and Meiosis Lab Manual 7.1-7.5 Fall 2024  Goals of this lab Concepts Outputs Understand the differences and similarities Used models to learn the steps of mitosis between mitosis and meiosis and meiosis Identify the phases of mitosis in cells Find both plant and animal cells in all stages of mitosis under a microscope, and Describe the mitotic differences between drawn pictures of all the stages plant and animal cells Understand the importance of crossing over  Today’s Activities 7.1: Modelling the Cell Cycle ○ using colored beads 7.2: Observing Mitosis in Plant Cells ○ prepared root tip slides 7.3: Observing Mitosis in Animal Cells ○ prepared whitefish blastula slides 7.4: Modelling Meiosis ○ back to the colored beads 7.5: Observing Meiosis in Sordaria ○ determining if ascocarp display crossing over.  Mitosis vs. Meiosis Mitosis Meiosis Is part of the cell cycle Is found in the life cycle of sexually reproducing organisms Generates two genetically identical cells Reduces diploid chromosome numbers by Carried out when an organism grows in half (makes them haploid) size or when worn out cells need to be replaced  Chromosomes Genome : the complete collection of all the genetic information of a cell DNA can exist as chromatin (DNA and histone protein complex) or in the form of chromosomes (highly condensed chromatin, coiled to fit into small spaces). Chromosomal number varies among organisms: most eukaryotes have 10-50 in their somatic (non-reproductive) cells- humans have 46 Chromosomes occur in pairs of homologous chromosomes (or homologues ) in somatic cells, making them diploid cells (2n) Gametes : reproductive cells (sperm and ova) with half as many chromosomes as somatic cells, making them haploid (n). Homologous Chromosomes Homologous chromosomes , or homologues , A pair of homologues (homologous chromosomes) have similar: Size Shape Centromere location Hereditary information (for the same A gene locus traits and situated in the same relative chromosomal location). A pair of alleles Homologues carry information on the same traits, but the information may vary (one is inherited from the mother, one from the father). Three pairs of genes  Eukaryotic cell cycle: two major phases Interphase Mitotic Phase (M phase)/ Cell Division Occupies 90% of the cell cycle, is the stage where a cell: A microtubular apparatus, known as the Grows in size & mass mitotic spindle , forms and binds to the Undergoes metabolic reactions replicated DNA organized into chromosomes Duplicates its DNA & cytoplasm Prepares for mitosis The spindle moves them apart, giving rise to two cells with identical genetic information Usually the longest part of the cycle. Can be divided into subphases: G1 phase (“first gap”) – Cell grows in size and undergoes normal metabolic activities S phase (“Synthesis”) – DNA replicated/synthesized, G2 phase (“second gap”) – The cell prepares for mitosis/cell division Eukaryotic cell cycle: two major phases Interphase  Chromosomes during the cell cycle During the G1 phase, each chromosome is a single structure, with a single centromere During the S phase each of the homologous chromosomes undergo replication , forming two identical copies called sister chromatids , joined together by a single centromere, and will be separated during division Centromeres are the narrow “waist” of the duplicated chromosome where the two chromatids are most closely attached. Humans have 23 pairs of homologous chromosomes. Chromosome Structure  M phase- two major events Mitosis Cytokinesis Division of the nucleus Division of the cytoplasm Consists of the separation of the sister Consists of the partition of two cytoplasms chromatids of the two daughter cells A continuous process, but described in five distinct subphases: ○ Prophase ○ Prometaphase ○ Metaphase ○ Anaphase ○ Telophase How the cell cycle works Exercise 7.1: Modeling the cell cycle and mitosis in an animal cell. You will use pop-beads and Key terms: magnetic centromeres to Haploid/Diploid model the following Homologous stages of the cell cycle Chromosomes and mitosis: Nuclear Envelope Interphase Chromatin M-phase Centrosome Mitosis Centrioles Prophase Nucleoli Prometaphase Sister Chromatids Metaphase Spindle Anaphase Kinetochores Telophase Chromosomes Cytokinesis Cleavage Furrow/Cell Plate  Prophase First subphase of mitosis: chromosomes condense, nuclear envelope begins to disintegrate, and the nucleolus disappears. Mitotic spindle begins to form: cables made of microtubules, extending from poles towards the centromeres of chromosomes Will continue to extend until attached attached to a centromere at a protein disc calle a kinetochore. In animal cells, this is facilitated by centrosomes (w/ the centriole pairs) after they’ve migrated to opposite ends/poles of the cell (no assistance needed for plant cells).  Prometaphase Nuclear envelope is disassembled. Chromosomes are at their greatest condensation. Each duplicated chromosome contains two kinetochores in its centromere region, which face in opposite directions A spindle fiber attaches each kinetochore to an opposing pole of the spindle Non-kinetochore fibers from opposite poles overlap and interact at the spindle equator  Metaphase The spindle apparatus is completely assembled. The centromeres of all the chromosomes are lined up at the spindle’s equator. Each of the chromosomes has one sister chromatid located on either side of the equator, creating the metaphase plate.  Anaphase The centromeres, which join the sister chromatids together, separate. When this occurs, sister chromatids of each chromosome are pulled apart, becoming daughter chromosomes. The daughter chromosomes move to the opposing poles of the spindle, which lengthens.  Telophase Chromosomes decondense. Spindle apparatus disintegrates. Two nuclear membranes form , one around each set of unduplicated chromosomes. These nuclear membranes are formed from remnants of the mother cell nuclear envelope and other components of the endomembrane system. Nucleoli reform.  Cytokinesis Occurs at the end of mitosis B (during anaphase and telophase) and is a division of the cytoplasm into roughly equal halves. Falls in the “M” phase, but not technically a subphase of mitosis. A The mechanism of cytokinesis differs between animal (A) and plant (B) cells.  Cytokinesis Animal Cells Plant cells Occurs by actin filaments contracting and A new cell wall is laid down at a right pinching the cell in two. angle to the mitotic spindle to divide the two daughter cells: this is the cell plate. Evident as a cleavage furrow that appears between the daughter cells. Cellular vesicles enclosing pectins derived from the golgi body come together at the spindle equator. A band of actin filaments is located on the inside of the cell membrane at the spindle Cellulose fibers are produced among the equator: this constricts when the myosin pectins leading to the formation of the cell motor proteins bind the microfilaments plate, and eventually the cell wall. tighter.  Animal cell cytokinesis Microtubules and actin-myosin communicate with each other to coordinate the cleavage plane and initiate furrowing. Furrowing based on contraction of the contractile ring, a bundle of aligned actin filaments alternating with myosins. Animal cells determine the furrow region in relation to the position and orientation of the mitotic apparatus.  Plant cell cytokinesis In terrestrial plants, cytokinesis occurs by cell plate formation. This involves the delivery of golgi-derived vesicles to the equator of the cell and the subsequent fusion of these vesicles with each other.  Results of Mitosis Two daughter nuclei. Each with the same chromosome number as parent cell. Chromosomes in unduplicated form.  Exercise 7.2: Observing mitosis and cytokinesis in plant cells Using prepared slides of onion (Allium) root tips, you will look for cells in each phase of mitosis. Draw all of the following phases: Interphase M phase Mitosis Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis  Allium (onion) root tip, L.S., 40X & 100X Dr. Iwantsch Fordham University  Allium interphase, L.S., 400X Dr. Iwantsch Fordham University  Allium prophase , L.S., 400X Dr. Iwantsch Fordham University  Allium prometaphase , L.S., 400X Dr. Iwantsch Fordham University  Allium metaphase, L.S., 400X Dr. Iwantsch Fordham University  Allium anaphase, L.S., 400X Dr. Iwantsch Fordham University  Allium telophase , L.S., 400X Dr. Iwantsch Fordham University  Allium cytokinesis, L.S., 400X Dr. Iwantsch Fordham University Exercise 7.3: Observing chromosomes, mitosis and cytokinesis in animal cells Locate and draw all the following phases: Interphase M phase Mitosis Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis What are the differences between mitosis in animal and plant cells?  Whitefish blastula, section, 40 & 100X Dr. Iwantsch Fordham University  Whitefish interphase, section, 400X Dr. Iwantsch Fordham University  Whitefish prophase, section, 400X Dr. Iwantsch Fordham University  Whitefish metaphase, section, 400X Dr. Iwantsch Fordham University  Whitefish anaphase, section, 400X Dr. Iwantsch Fordham University  Whitefish telophase, section, 400X Dr. Iwantsch Fordham University  Whitefish cytokinesis, section, 400X Dr. Iwantsch Fordham University  Meiosis and the life cycle of sexually reproducing organisms The alternation of meiosis and fertilization is found in all sexually reproducing organisms (mechanism that preserves chromosome number). Meiosis is involved in extremely different ways in the life-cycle of multicellular eukaryotes: Fungi Plantae Animalia Organisms belonging to each of these kingdoms show differences in respect to the timing of meiosis and fertilization.  The stages of meiosis Two successive nuclear divisions: meiosis I and meiosis II Meiosis I Meiosis II DNA is replicated only once beforehand Preceded by brief interphase, no DNA replication Separates the homologous pairs Separates replicate sister chromatids (non-identical because of the crossing over in meiosis I) Results in two haploid cells A mitotic division of the products of meiosis: results in Stages: four haploid cells overall Prophase I Metaphase I Stages: Anaphase I Prophase II Telophase I Metaphase II Anaphase II Telophase II  Key Fig. 13-6a Haploid (n) Diploid (2n) n Gametes n n MEIOSIS FERTILIZATION Zygote 2n 2n Diploid multicellular Mitosis organism (a) Animals  Crossing over Occurs between two non-sister chromatids of homologous chromosomes (attracted by synapsis ) The chromatids break in the same place Sections of chromosomes are exchanged The result is a hybrid chromosome Chiasmata : X-shaped areas where segments of the homologous chromosomes have swapped genetic information  Prophase I Similar to prophase in mitosis, except: Synapsis-duplicated homologous chromosomes line up together as a pair, forming a tetrad : a complex containing two pairs of sister chromatids This is when crossing over occurs  Metaphase I Similar to metaphase in mitosis, except: Homologous chromosomes line up at the equator of the spindle as tetrads , by random orientation : The individual homologues randomly face different poles, resulting in gametes with different combinations of parental chromosomes This process is called independent assortment:  Anaphase I Similar to anaphase in mitosis, except: Reduction division takes place (2N → N) Homologous pairs separate and individual homologues move to each pole The centromere does not split, and the sister chromatids remain attached Each daughter cell gets both sister chromatids of one of the members of each homologous chromosome pair  Telophase I Similar to telophase in mitosis except: Some events might not go to completion, since the cell has a brief interphase and then immediately begins meiosis II Cytokinesis produces two haploid cells (n)’ sister chromatids are still aligned, but there are half as many as at the start  Prophase II Similar to prophase in mitosis: New spindle forms to attach to chromosome clusters  Metaphase II Similar to metaphase in mitosis: Spindle fibers bind to both sides of the centromere Individual chromosome align along central plane  Anaphase II Similar to anaphase in mitosis: sister chromatids move to opposite poles  Telophase II Similar to telophase in mitosis: Nuclear membrane reforms Nucleoli reappear Spindle apparatus disassembles Chromosomes decondense After cytokinesis, we are left with four haploid (n) daughter cells  A comparison of mitosis and meiosis Meiosis has two unique features not found in mitosis: Synapsis The process of drawing together homologous chromosomes down their entire lengths so that crossing over can occur Reduction division Meiosis involves two nuclear divisions but only one DNA replication, the final amount of genetic material passed to the gametes is halved.  Exercise 7.4: Modeling Meiosis Use pop beads to model the steps of the cell cycle Key Terms: and meiosis, including crossing over. Meiosis I Meiosis II Complete table 7.1 Synapses Tetrad Crossing over Chiasma Alleles  Spore formation and crossing over Sordaria – Ascomycete fungus, spends most of its life cycle as a haploid. Two 2n strains (each w/ a different allele for spore color), fuse to form 2n zygote. Zygote then forms two haploid strains (n), and undergoes meiosis I, meiosis II, and one round of mitosis (eight haploid cells). Since the cells (spores) are haploid, genotype = phenotype. The allele of their spore color gene can therefore be determined visually. If crossing over: the phenotypic sequence of spore color changes. If no crossing over: four ascospores on one each side of the ascus will be the same color. Ascus Ascus - a sac containing eight linearly distributed cells (ascospores), the end results of meiosis and one round of mitosis. We will be analyzing the organization of the spores within the asci. Sordaria life cycle Exercise 7.5: Meiosis in Sordaria fimicola: a study of crossing over You will visual crossing over looking at images of Sordaria. Complete discussion questions and Table 7.2. Key terms: Chiasma, Sordaria, Ascus Ascocarp Ascospores  Parental and Crossover Phenotypes: (a) All one color (tan) (b) All one color black (c) Non-crossing over (d) Crossing over (e) Crossing over Exercise 7.5: Meiosis in Sordaria fimicola: a study of crossing over Crossing over? NO YES YES MAYBE  Summary of Outputs Postlab Notebook See it on Blackboard!! Pictures for 7.2, 7.3 Questions throughout the exercises Table 7.1, 7.2 Reviewing your knowledge