Chromosome Numbers of Some Common Organisms

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1 Meiosis Introduction Process of reduction division Purpose: Produces gametes (sex ) sperm & egg Meiosis is NOT a cycle like mitosis Diploid vs. Haploid Diploid a cell that contains homologous chromosomes (one from each parent) represented by the symbol 2n Found in somatic or body (ex. Skin, digestive tract) Example : Humans 2n = 46 Haploid a cell that contains only a single set of chromosomes (one from either parent, not both); represented by the symbol n Found in gametes or sex sperm & egg Example: Humans n = 23 4 Chromosome Numbers of Some Common Organisms 5 Meiosis Introduction Similar to Mitosis IPMATC Meiosis involves two distinct divisions, called Meiosis I and Meiosis II By the end of Meiosis II, the 1 diploid cell that entered meiosis has become 4 haploid 6 Interphase Stage before prophase I (no interphase before prophase II) Contains: centrioles and chromatin Made of stages: G1 basic cell growth S replication and repair of DNA G2 final preparation for cell division Prophase I Corresponding homologous chromosomes from each parent pair up to form homologous pairs When homologous chromosome overlap its called crossing over. Prophase I Crossing over happens when parts of the homologues chromosomes switch places after overlapping

2 Metaphase I The centrioles send out spindle fibers to line up homologous pairs in the middle of cell along the metaphase plate Anaphase I The centrioles use the spindle fibers to separate the homologous pairs Each homologous chromosome is pulled to the opposite pole of the cell. If the centrioles do not properly attach the spindle fibers to the homologous chromosome before they start to pull, then a Nondisjunction will occur Nondisjunction in Meiosis I Telophase I & Cytokinesis Telophase I the cell creates a temporary nucleus around the two homologous chromosome sets Cytokinesis the cell divides into two Meiosis II The two new produced by meiosis I now enter a second meiotic division The do NOT replicate DNA resulting in four haploid Each cell has half of the original DNA 2n 2 = n Prophase II Each of the Meiosis II stages are running in 2 at the same time. Similar to Prophase of Mitosis Centrioles attach spindle fibers to the chromosomes Metaphase II Similar to Metaphase of Mitosis Centrioles use spindle fibers to line up the chromosomes in the middle at the metaphase plate Anaphase II The centrioles use the spindle fibers to separate the chromosomes into individual chromatids Each chromatid is pulled to the opposite pole of the cell If the centrioles do not properly attach the spindle fibers to the chromosome before they start to pull, then a nondisjunction will occur Nondisjunction in Meiosis II Each of the Meiosis II stages are running in 2 at the same time. Similar to Prophase of Mitosis Centrioles attach spindle fibers to the chromosomes

3 Telophase II & Cytokinesis Telophase II the creates a permanent nucleus around the two haploid chromosome sets Cytokinesis the divides into four haploid daughter 19 Mitosis Meiosis Number of Starting 1 Diploid cell 1 Diploid cell Number of ending 2 Diploid Cells 4 Haploid Cells Start: Number of Human 46 (Diploid, two 46 Chromosomes sets ) End: Number of Human (Haploid, one Chromosomes set ) Genetic Make up of Produces 2 identical Produces 4 unique Type of Somatic Body Gamete sex Science Classroom Rules 1. Listen And Follow Directions 2. Raise Your Hand Before Speaking Or Leaving Your Seat 3. Respect Your Classmates And Your Teacher 4. Keep Hands, Feet, And Objects To Yourself 2/22/ Instructions for Cell Cycle Foldable Page 127 IMPORTANT!!! Use your Cell Cycle Notes from this week to help you!!! 26 3

4 Folding and Cutting Your paper should already be folded and cut from yesterday (if not, have someone who knows how to do it show you!) Your foldable should look like the picture to the right On the TOP tab on the RIGHT side, label G 1 Phase at the top of the tab (like a title) Label the tab below it (2 nd tab on the RIGHT side) S Phase Label the tab below it (3 rd tab on the RIGHT side) G 2 Phase Label the LAST tab on the RIGHT side PROPHASE On the BOTTOM tab on the LEFT side, label METAPHASEat the top of the tab (like a title) Label the tab above it (3 rd tab on the LEFT side) ANAPHASE Label the tab above it (2 nd tab on the LEFT side) TELOPHASE Label the TOP tab on the LEFT side CYTOKINESIS Label steps of the Cell Cycle in the circle on the inside of the foldable (as shown in this picture) Draw a picture of what the cell looks like in each phase of the Cell Cycle on the outside of the tabs (under the titles you wrote earlier) Drawing On the inside of the tabs on the RIGHT side, write a brief description of what happens during those phases On the inside of the tabs on the LEFT side, write a brief description of what happens during those phases Color the G1, S, and G2 sections of the circle (on the inside) LIGHT BLUE Color the phases of mitosis in the circle (on the inside) ORANGE Color the G1, S, and G2 tabs (outside and inside) LIGHT BLUE Color the phases of mitosis tabs (outside and inside) ORANGE 4

5 Chromosomes PURPLE Cytoplasm YELLOW Cell Membrane RED Nuclear Membrane - GREEN 5