Why produce identical cells? • Somatic cells contains 2 sets of chromosomes, maternal and paternal = diploid, 2n • Gametes (sperm and ovum) have only __one_________ set of unpaired chromosomes = haploid, n • Each organisms has its own fixed number of chromosomes, e.g. human has 46 chromosomes (23 pairs). • Producing identical cells preserves the ___original genetic________ number of chromosomes.
Significance of mitosis • Produces new cells for growth, repair and replace damaged or dead cells. • Forms asexual reproduction in unicellular organisms. • Ensures new cells are ____identical______ to parent cells. • Preserves the ___diploid________ number of chromosomes of species.
The Cell CycleSeries of cellular Interphasereproductive events inwhich duplication ofcell content and celldivision occur in anorderly sequence G1 SCytokinesis telophase anaphaseMitosis G2 metaphase prophase Mitotic (M) phase
Cell Cycle • Consist of 2 major phases: Phase 1: Interphase Phase 2: Mitotic phase (M phase) • Interphase involves ___stages/phases________ for cell division – It has 4 subphases: G0 G1, S, G2 – G1, G2: cell growth, produce proteins and organelles, cell differentiation – S: synthesis of DNA, duplication of chromosomes and replication of DNA • M phase, the cell divides – Includes mitosis (nuclear division) and cytokinesis (cytoplasmic division)
• Chromosomes are ___copied________ (# doubles) • Chromosomes appear as threadlike coils ____chromatin_______ at the start Cell membraneNucleus Cytoplasm
• Chromosomes condense • Centrioles (or poles) appear and begin to move to __opposite_________ end of the cell. • Nuclear membrane disappear • Nucleolus disappear • Spindle fibers form between the poles. CentriolesSisterchromatids Spindle fibers
• Two new nuclei form.• Chromosomes appear as chromatin (threads rather than rods).• 2 sets of chromosomes one at each__end_______• Spindle fibres disappear• Nucleolus & nuclear membrane are formed• Mitosis ends. Nuclei Nuclei Chromatin
CYTOKINESIS (PLANT)• In plant cells, cytokinesis starts with formation of cell plate at the ___________ of cell• Cell plate enlarges until it ___________ with plasma membrane• New cell wall is produced and separates the two daughter cells
MITOSIS ANIMAL PLANTSimilarities:Two identical cells are formed at the end of a divisionThey produce more cells and cause growthDifferences:Centrioles found at each pole No centrioles during mitosis (cortical microtubules) Mainly localized in special regions called meristems to Cells divide everywhere, all either elongate the tips of the time stems and roots or expand the girth of the plantFormation of cleavage furrow Formation of cell plate that at the equatorial plane grow outwards
REGULATION OF CELL CYCLE • The cell cycle is controlled by ___regulatory__ proteins __ in the cytoplasm • Each type of cell has its own timing • Some has frequent division
Controlled Mitosis • The ability of cell to divide at its own timing and rate • Enables __normal_________ growth and development and maintenance for perpetuity of living things
Uncontrolled Mitosis • If the genes that regulate the cell cycle are damaged or mutated, cell divide __abnormal___cell growth_____ • Cause: – Harmful ray: nuclear radiation, UV ray – Viruses – Carcinogenic chemicals: food additives, benzo (α) pyrene in cigarette smoke
The Effects of Uncontrolled Mitosis • Unregulated and very fast division increase the number of abnormal cells • Form an abnormal mass – tumour • Types of tumour: Brain – Malignant cancer • Invasive by metastasis Breast • Cancer cancer – Benign • Localize What is the treatment of • Does not cause cancer? serious problems • Remove by ___________
Mitosis Application: CLONING • The process to produce genetically identical cells / tissues / organisms / population from the mitosis of a single parent cell (clone) • Naturally: asexual reproduction, vegetative propagation (plant) • Artificially: cloning (animal), tissue culture (plant) Why? – Increase quantity – Improve quality – Ensure uniformity of traits
Animal CloningCloning is carriedout by replacingnucleus of an_________donor_____ egg cell with thenucleus of a diploidcell
ADVANTAGES OF CLONING• rapid multiplication, mass production in short time• genetically identical, desirable traits inherited and propagated• therapeutic cloning, replace damaged or diseased tissues / organs• fetal cell cloning, early detection of genetic defects• no seeds / difficult to germinate, propagate endangered or rare species
DISADVANTAGES OF CLONING• no genetic variation, susceptible to changes and new diseases, extinction• possibility of mutations, harmful effects of GMF• grow old quickly, shorter lifespan• exclusion of certain species, decrease biodiversity• traits transfer to wild species, creation of superweeds
What is Meiosis? • Meiosis produces daughter cells that have one half the number of chromosomes as the parent cell. • Meiosis enables organisms to reproduce sexually. • Meiosis involves two divisions producing a total of four daughter cells.
Summary of the Phases of Meiosis • meiosis 1: prophase 1, metaphase 1, anaphase 1, and telophase 1 • meiosis 2: prophase 2, metaphase 2, anaphase 2, and telophase 2 • In the first meiotic division, the number of cells is doubled but the number of chromosomes is not.
Meoisis Metaphase1 and Metaphase 2Independent Assortment
Meoisis-ProphaseThe homologous chromosomes pair up as thechromosomes coil upThe nuclear membrane begins to disintegrateCentrosomes begin moving apart.
• Synapsis (joining) of homologous chromosomes produces tetrads (also called _bivalents_____________).• The two chromosomes may exchange fragments between non-sister chromatids by a process called __crossing over____________
Meoisis-Metaphase Bivalents become aligned in the __center____________ of the cell and are attached to spindle fibers.
Independent AssortmentRandom arrangement of pairs of chromosomes.
Meosis-Anaphase IAnaphase I begins when homologous chromosomes______separate________.
Telophase IThe nuclear envelope reforms and nucleoli reappear.This stage is absent in some species.
Variation • Sexual reproduction promotes variation because each gamete (sperm or egg) contains a mixture of genes from two different parents. • Crossing-over and Independent assortment promote variation. • Variation is necessary for __natural selection____________.
Significance of Meoisis • Genetic Diversity through Crossing Over: • Prophase I • Genetic Diversity through Independent Assortment: • During Metaphase I
Review • Understand why cells duplicate • What is interphase? Follow the phases of interphase • Describe the major events of mitosis and cytokinesis and understand what occurs at each stage-KNOW THE ORDER • Discuss how mitosis relates to cancer • Understand Cloning • Understand why we need meiosis • Describe the major events that occur during the separate divisions of meiosis-KNOW THE ORDER • Describe how mitosis and meiosis differ • Understand significance of synapsis and crossing over • Be able to read a slide and identify the stage • Describe Binary Fission • Describe Aneuplody
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