CELL CYCLE, MITOSIS AND MEIOSIS NOTES

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1 CELL CYCLE, MITOSIS AND MEIOSIS NOTES DNA - Genetic information is stored in the DNA strand in the form of genes. DNA stands for deoxyribose nucleic acid Genes located on the DNA strand 2 Types of DNA strands Chromatin Normal DNA, found during INTERPHASE (everyday life of the cell) Thin thread like coils, not visible by microscope Chromosomes Packaged DNA, found during MITOSIS (cell division) Thick condensed super coiled DNA Chromatid 1 part of a chromosome Sister Chromatid a copy of the original chromatid Centromere point where two chromatids attach Chromosome Number each species has its own chromosome number parent Homologous chromosomes A pair of chromosomes having the same gene sequence, each derived from one Mom Dad Eventually each homologous chromosome will form a sister chromatid before mitosis Diploid (2N) two sets of DNA one from each parent Haploid (N) one set of DNA Found in sex cells (egg, sperm)

2 CELL CYCLE the sequence of events that occurs in a cell from mitosis to mitosis 5 events -3 phases of Interphase, G 1, S, G 2 -Mitosis -Cytokinesis (which is really a part of mitosis) INTERPHASE the everyday life of the cell Divided into 3 phases G1 phase cell growth, cell doubles in size, protein production S phase DNA replication (copies itself) G2 phase rapid cell growth, prep for cell division DNA is in the form of Chromatin long thin strands of DNA tangled up in the nucleaus

3 MITOSIS division of the nucleus Mitosis is the division of the cell nucleus in which the chromosomes in the parent cell divide into two identical sets of cells with the same chromosome number as the parent. Evolutionary Significance is to maintain the chromosome number. Mitosis occurs in somatic cells (body cells or non sex cells). Cell size causes the cell to divide. When the volume of the cell becomes larger than the surface area, mitosis occurs. Mitosis occurs in 4 phases Prophase, Metaphase, Anaphase, Telophase PROPHASE Early Prophase Chromatin coils and condenses into chromosomes Nuclear membrane and nucleolus disappears Centrioles move to opposite ends or poles of the cell Middle Prophase Spindle fibers form across the cell from centriole to centriole and attach to Kinetochore fibers. Kinetochore fibers extend from the centromere to the centrioles and help control movement of chromosomes Late Prophase Asters form Spindle Fibers Aster

4 METAPHASE Kinetochore fibers move the chromosomes to the center of the cell Chromosomes line up at the center of the cell (cell equator) ANAPHASE Centromere of each pair of chromatids divides Chromosomes separate Chromatids move to opposide poles of the cell

5 TELOPHASE Cytokinesis (division of the cytoplasm) occurs Identical sets of chromatids at opposite poles Centrioles and spindle fibers disappear Chromatids unwind and elongate back into chromatin Nuclear membrane and nucleolus reform Cell Plate Cleavage Furrow CYTOKINESIS division of the cytoplasm, this is really a part of Telophase In animal cells cell pinches inward forming a cleavage furrow to form two new daughter cells In plant cells cell forms a cell plate which develops into a cell wall separating the two daughter cells MITOSIS RESULTS 2 DIPLOID IDENTICLE DAUGHTER CELLS

6 Results : 4 haploid gametes MEIOSIS reduction division, produces gametes (sex cells, egg and sperm) Meiosis I Meiosis II Process of reduction division that produces gametes in which the number of chromosomes per cell is cut in half (haploid) through the separation of homologous chromosomes. Homologous Chromosomes chromosomes that have a corresponding chromosome from the opposite sex parent. Diploid (2N) A cell that contains both sets of homologous chromosomes is diploid, which means two sets Haploid (N) A cell that contains only one set of chromosomes is haploid.

7 CELL CYCLE -3 phases of Interphase, G 1, S, G 2 -Meiosis I and Meiosis II -Cytokinesis INTERPHASE Just like interphase before mitosis G1 phase cell growth, cell doubles in size, protein production S phase DNA replication (copies itself) G2 phase rapid cell growth, prep for cell division MEIOSIS I PROPHASE I Chromatin coils into chromatids and the homologous pairs of each come together to form a tetrad Tetrad - A four-part structure that forms during prophase I of meiosis I and consists of two homologous chromosomes, each composed of two sister chromatids. Crossing over - The exchange of genetic material between two paired chromosomes (Tetrad). Crossing over is important because it is a way to recombine the genetic material so that each person (except for identical twins) is genetically unique. METAPHASE I Tetrads line up at the equator of the cell ANAPHASE I Homologous Chromosomes separate and are pulled to the poles of the cell (the centromeres do NOT split) TELOPHASE I Chromosomes uncoil, spindle breaks down, the nuclear membrane and nucleoli reform Cytokinesis occurs ( division of the Cytoplasm) to form two cell NOTE: THERE IS NO INTERPHASE BETWEEN MEIOSIS 1 AND MEIOSIS II MEIOSIS II just like Mitosis except that there is only half the number of chromosomes PROPHASE II - METAPHASE II - ANAPHASE II - TELOPHASE II - CYTOKINESIS MEIOSIS RESULTS 4 HALPLOID (N) GAMETES

8 Comparison of Meiosis and Mitosis MEIOSIS RESULTS 4 HALPLOID (N) GAMETES MITOSIS RESULTS 2 DIPLOID IDENTICLE DAUGHTER CELLS

9 MITOSIS 11. What moves the chromatids during mitosis? 12. What anchors the spindle? 13. What are the four phases of mitosis? 14. How many daughter cells are created from mitosis and cytokinesis? 15. During what phase does cytokinesis begin? 16. If a human cell has 46 chromosomes, how many chromosomes will be in each daughter cell? 17. If a dog cell has 72 chromosomes, how many daughter cells will be created during a single cell cycle? Each of these daughter cells will have how many chromosomes? 18. The nuclear membrane dissolves during what phase of cell division? 19. In the cell pictured above how many chromosomes are present during prophase? 20. What structure holds the individual chromatids together?

10 Phases of Meiosis Name of Phase Description 1. Homologous chromosomes pair up and form tetrad 2. Spindle fibers move homologous chromosomes to opposite sides 3. Nuclear membrane reforms, cytoplasm divides, 4 daughter cells formed 4. Chromosomes line up along equator, not in homologous pairs 5. Crossing-over occurs 6. Chromatids separate 7. Homologs line up alone equator 8. Cytoplasm divides, 2 daughter cells are formed

11 1. is a kind of cell division that produces haploid cells with ½ the number of chromosomes of the parent cell. a. mitosis b. meiosis 2. Cells undergo meiosis to a. grow bigger b. repair injuries c. replace worn out cells d. make gametes 3. A group of 4 chromatids that forms during synapsis is called a a. biad b. triad c. tetrad d. quadrad 4. The exchange of genetic material between arms of homologous chromosomes is called a. synapsis b. independent assortment c. asexual reproduction d. crossing over 5. During meiosis, crossing over happens in a. prophase I b. metaphase I c. prophase II d. interphase II 6. During meiosis a 2n parent cell divides to produce a. four identical 2n cells b. two identical 2n cells c. two identical 1n cells d. four different 1n cells 7. DNA located in the cell during Interphase is in the form of a. Chromatin b. Chromosomes 8. Division of the cytoplasm is called a. mitosis b. cytokinesis c. replication d. diploid 9. Reduction division is used to describe what type of cell division? a. mitosis b. meiosis What is the end result of Mitosis? What is the end result of Meiosis?