Transcript Chromosomes
Chromosomes Chromosome Formation ChromosomesROD Shaped structure made of DNA and Protein Histone ProteinsHelp maintain shape of the chromosome Structure of a Chromosome CENTROMERE CHROMATID CHROMATID Homologous ChromosomesHumans have AUTOSOMES Humans Have 44 Autosomes SEX CHROMOSOMES Humans have 2 Male XY Female XX 46 chromosomes 23 homologous pairs CHROMOSOME NUMBER 2n Chromosomes Honeybee (female) – 32 Adder’s Tongue Fern - 1262 Human - 46 Cat - 38 Common Frog - 26 Maize - 20 Does more chromosomes bigger Chromosome number mean doesanot or more complicated organism? determine complexity of organism DIPLOID CELLS VS. HAPLOID CELLS Diploid 2N= Contains both autosomes in a homologous pair Haploid 1N= Contains 1 autosome of homologous pair Human Body Cells are Diploid Human sex cells are Haploid Egg and Sperm Cell Contain 46 chromosomes and 23 pairs Contain 23 Chromosomes and no pairs Mitosis vs. Meiosis 46 46 23 23 46 46 23 MITOSIS 23 23 MEIOSIS 23 HOMOLOGOUS CHROMOSOMES Cell Division Eukaryotes vs. Prokaryotes Prokaryotes vs. Eukaryotes Characteristics Prokaryotes Single celled organisms No membrane bound nucleus or organelles Simple and smaller Eukaryotes Make up multicellular organisms Have membrane bound organelles and nucleus Complex and Larger Many chromosomes Have a cell wall DNA located in the nucleus Few chromosomes Chromosomes coil and condense before cell division Prokaryotic Cell Division • Binary fission • Division of prokaryotic cell into two offspring cells Cell Division in Eukaryotes Cell Division occurs in two stages Mitosis/Meiosis Division of the nucleus Four stages (Prophase, Metaphase, Anaphase, Telophase) Cytokinesis Division of the cytoplasm Prokaryotic vs Eukaryotic Cell Division Prokaryotes DNA is circular and attached to the plasma membrane DNA does not wrap around proteins to form chromosomes before cell division Binary Fission(most cells) Cell membrane will develop between the two copies of DNA Cell Doubles in size Cell membrane pinches off Cell Wall forms around new cell membrane Eukaryotes Chromosomes coil and condense before cell division Consists of 2 Divisions 1)Division of the nucleus Mitosis – body cells(Diploid Cells) Meiosis- sex cells (Haploid cells) 2) Division of the Cytoplasm Cytokinesis What is the same in Euk and Prok cell division? Create new cells Genetically identical DNA is copied before cell division Cytoplasm will divide Eukaryotic Cell Division Cell Cycle CELL CYCLE- Repeating set of events in the life of the cell Interphase-longest stage in the cell cycle G1 – Cell growth (cell grows to a mature size) S – DNA is copied (double the amount of DNA) G2 – Growth and preparation for cell division G0-Cells that do not divide will remain in G0 (occurs at the end of G1) Cell division Mitosis/Meiosis – Nucleus divides Cytokinesis – Division of the cytoplasm What triggers the cell to leave on phase and move to the next? Checkpoints = traffic signal Proteins regulate the process Three main checkpoints G1 checkpoint(end of G1) G2 checkpoint (during G2) Mitosis checkpoint (toward the end of mitosis) Control of Cell Division G1 checkpoint-Cell Growth Checkpoint Checks to see if the cell is healthy and has reached a mature size Will determine if the cell will divide G2 checkpoint-DNA synthesis checkpoint DNA repair enzymes check the results of DNA replication Mitosis checkpoint If cell passes this checkpoint, the cell will exit Mitosis and move into G1 of interphase What happens if there is a mutation in one of these proteins? Organelle Review Centrosomes Contain two centrioles Made of microtubules Acts as anchors in cell division Plants centosomes do not contain centrioles Mitotic Spindle fibers-Two Main types Kinetochore Fibers- Attach from centriole to centromere of chromosomes and assists in movement of chromosomes Polar Fibers – Extend from pole to pole and keep the shape of the cell during cell division Organelle Review Nuclear envelope • Double Phospholipid bilayer surrounding nucleus • Surrounds the DNA Nucleolus • Dense area where DNA is concentrated in the nucleus • Ribosomes (rRNA) is synthesized MITOSIS Division of the nucleus Forms two identical daughter cells Four phases Where does it occur? Somatic Cells (Body cells) Why does it occur? • Asexual reproduction • Growth and development • To replace old cells or dying cells Prophase • Chromatin coils and condenses into chromosomes • Nucleolus and nuclear membrane break down and disappear • Centrosomes appear and move to opposite ends of the cell • Spindle Fibers appear: Kinetochore fibers extend from kinetochore of each chromatid to centrosome. Metaphase Metaphase = Middle Kinetochore fibers move chromosomes to center of the cell All chromosomes line up in a single file line 46 chromosomes lined up in the middle (Humans) Anaphase Anaphase • Chromosomes separate at the centromere and chromatids move to opposite poles • Chromatids are now considered individual chromosomes Telophase • Chromosomes are on opposite sides of the cell • Centrioles disappear and Spindle fibers disassemble and disappear • Chromosomes unwind into less tightly coiled chromatin • Nuclear envelope forms around each set of chromosomes • Nucleolus forms in each of the newly forming cells Animation CYTOKINESIS Cytokinesis-the division of the cytoplasm Animal cells: Pinching inward of the cell membrane occurs. Called Cleavage furrow In plants cell plate formation Which stage? Mitosis vs. Meiosis Where do they occur? Mitosis – in the body cells Meiosis – in the germ cells Why does it occur? Mitosis • Asexual reproduction • Growth and development • To replace old cells Meiosis • Formation of gametes (egg and sperm cells) that will be used in sexual reproduction Mitosis vs. Meiosis 46 46 23 23 46 46 23 MITOSIS 23 23 MEIOSIS 23 Meiosis Also known as reduction division Occurs in germ cells found in the ovaries and testes Produces sex cells which are haploid Occurs in two phases Meiosis I • Reduces the number of chromosomes from diploid to haploid Meiosis II • Produces four haploid daughter cells Meiosis I Meiosis I Prophase I DNA coils tightly into chromosomes Spindle fibers and centrosomes appear Nucleolus and nuclear envelope disassemble Synapsis =Pairing of homologous chromosomes Tetrad =Pair of homologous chromosomes twisted around each other Crossing over may occur Genetic recombination Meiosis I Metaphase I • Tetrads line up along midline • Independent assortment occurs Anaphase I • Homologous chromosome pairs(Tetrads) are separated and move to opposite poles (Independent assortment occurs) Telophase I • Chromosomes reach opposite ends of cell • Spindle Fibers disappear • In some cells the nuclear envelope will reappear • Cytokinesis begins Meiosis II Meiosis II Prophase II Spindle fibers form and attach to the centromere of the double stranded chromosomes. (Nuclear envelope will disappear if it was created) Metaphase II Double stranded chromosomes are moved to the midline of the dividing cell Anaphase II Chromatids separate and move toward opposite poles Telophase II Nuclear membrane forms and nucleolus reappears, spindle fibers and centrosomes disappear, chromatin uncoils into chromosomes Cytokinesis II Division of the cytoplasm occurs resulting in four new cells Each cell contains half the original amount of chromosomes Mitosis vs. Meiosis Development of Gametes in Animals Spermatogenesis produces Sperm or Spermatozoa produces four Oogenesis Cytoplasm is divided unequally Produces one mature egg cell or Ova Polar bodies are the three other products of meiosis and they will eventually degenerate.