Roles of Cell Division. Reproduction - Like begets like, more or less. Examples of Cell Numbers. Outline Cell Reproduction

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1 Outline Cell Reproduction 1. Overview of Cell Reproduction 2. Cell Reproduction in Prokaryotes 3. Cell Reproduction in Eukaryotes 1. Chromosomes 2. Cell Cycle 3. Mitosis and Cytokinesis 4. Sexual Life Cycle & Meiosis Reproduction - Like begets like, more or less Living organisms reproduce by two methods Asexual reproduction Offspring are identical to the original cell or organism Involves inheritance of all genes from one parent Sexual reproduction Offspring are similar to parents, but show variations in traits Involves inheritance of unique sets of genes from two parents Copyright 2009 Pearson Education, Inc. Roles of Cell Division Asexual reproduction Reproduction of an entire single-celled organism Growth of a multicellular organism Growth from a fertilized egg into an adult Repair and replacement of cells in an adult Sexual reproduction Sperm and egg production Examples of Cell Numbers Human Body 50,000,000,000,000 cells Red blood cells 25,000,000,000 RBCs replaced every day 1,400,000,000 Intestinal Epithelium Cells Last 1.5 days Copyright 2009 Pearson Education, Inc. 1

2 Figure 8.3A Binary fission of a prokaryotic cell Genome Size Varies Prokaryotic chromosome Plasma membrane 1 Cell wall Duplication of chromosome and separation of copies Protein Ring 2 Cell elongation and movement of DNA copies 3 Division into two daughter cells Prokaryotic Chromosomes Eukaryote Chromosome Structure Chromatids Chromosome Structure Centromere Chromosome Replication Chromosome DNA Histone Protein Chromatids Centromere 2

3 Chromosome Duplication & Distribution Centromere Chromosome duplication Sister chromatids Karyotype of Human Chromosomes Chromosome distribution to daughter cells Chromosome Numbers The cell cycle multiplies cells The cell cycle is an ordered sequence of events for cell division It consists of two stages Interphase: duplication of cell contents G 1 growth, increase in cytoplasm S duplication of chromosomes G 2 growth, preparation for division Mitotic phase: division Mitosis division of the nucleus Cytokinesis division of cytoplasm Copyright 2009 Pearson Education, Inc. 3

4 G 1 Cytokinesis Mitosis INTERPHASE G 2 Mitotic Phase M Chromosomes condense and chromatids separate S C Cytoplasm separates Cytokinesis Cell Cycle of Eukaryotes INTERPHASE G1 - Primary Growth S - DNA Synthesis G2 Mitochondria replicate Chromosomes condense Mitosis in Eukaryotes Mitosis Separation of Chromosomes Division of Nucleus Stages of Mitosis Prophase Metaphase Anaphase Telophase The stages of cell division Figure 8.6 The stages of cell division (part 2) LM 250 INTERPHASE PROPHASE PROMETAPHASE Centrosomes Mitotic Centrosome Nuclear Chromatin spindle Envelope Fragments Kinetochore METAPHASE ANAPHASE TELOPHASE Spindle Nucleus Plasma membrane Chromatids Centromere Spindle Microtubules Metaphase plate Chromatids Separating Nuclear envelope forming 4

5 Figure 8.7A Cytokinesis in an animal cell Cell plate formation in a plant cell Wall of parent cell Cell plate Daughter forming nucleus Cleavage furrow Cleavage furrow SEM 140 Contracting ring of microfilaments Cell wall New cell wall Daughter cells Vesicles containing cell wall material Cell plate Daughter cells Mitosis in Plant Cells INTERPHASE (cell growth and chromosome duplication) S (DNA synthesis) G 1 Cytokinesis Mitosis (division of (division cytoplasm) of nucleus) G 2 Genetically Identical daughter cells MITOTIC PHASE (M) 5

6 Applying Knowledge about Cell Division Controlling the Cell Cycle Human cells have 46 chromosomes. By the end of interphase G 0 G 1 checkpoint How many chromosomes are present in one cell? How many chromatids are present in one cell? G 1 M Control system G 2 S M checkpoint G 2 checkpoint Figure 8.9A Copyright 2009 Pearson Education, Inc. Controlling the Cell Cycle Controlling the Cell Cycle Growth factor Plasma membrane Receptor protein Relay proteins Cyclins & Cyclin- Dependent Kinases G 1 checkpoint Signal transduction pathway G 1 Control system S M G 2 Figure 8.9B 6

7 Cancer cells produce tumors Cancer cells escape controls on the cell cycle Cancer cells divide rapidly Tumor Tumors Lymph vessels Blood vessel They spread to other tissues through the circulatory system Growth is not inhibited by other cells, and tumors form Benign tumors remain at the original site Malignant tumors spread to other locations by metastasis Single cancer cell. Invade Neighboring Tissue Metastasize Cancer cells escape controls on the cell cycle Cancer cells divide rapidly Growth is not inhibited tumors form Benign tumors remain at the original site Malignant tumors spread to other locations by metastasis Copyright 2009 Pearson Education, Inc. Interfering with Cell Division Radiation Chemotherapy END END Mitosis Mitosis Periwinkle - Vinblastin Pacific Yew - Taxol 7

8 Meiosis Learning Goals Meiosis 1. Understand the differences between homologous chromosomes and sister chromatids. 2. Distinguish between 1. autosomes and sex chromosomes. 2. somatic cells and reproductive cells 3. diploid cells and haploid cells. 3. Describe and recognize the events of meiosis 4. Describe similarities & differences between mitosis and meiosis. 5. Explain how meiosis contributes to genetic variation in sexually reproducing organisms. Sexual Life Cycle Meiosis Multicellular diploid adults (2n = 46) Haploid gametes (n = 23) n Egg cell n Sperm cell Diploid zygote (2n = 46) Fertilization 2n 8.13 Gametes have a single set of chromosomes Meiosis is a process that converts diploid cells to haploid cells Diploid cells have two sets of homologous chromosomes Haploid cells have one set of chromosomes Meiosis occurs in the sex organs, producing gametes sperm and eggs Fertilization is the union of sperm and egg The zygote has a diploid chromosome number, one set from each parent Mitosis and development Copyright 2009 Pearson Education, Inc. 8

9 Preparation of a karyotype from a blood sample Diploid Organisms have Pairs of Homologous Chromosomes Blood culture Centrifuge Hypotonic solution Fixative White blood cells Stain Homologous Chromosomes Centromere Homologous chromosomes 4 5 2,600 Sister chromatids Homologous chromosomes have similar genetic information Homologous Pair Coat-color genes Brown C c White Eye-color genes Black E e Pink Meiosis I Prophase I Metaphase I Anaphase I Telophase I Stages of Meiosis Meiosis II Prophase II Metaphase II Anaphase II Telophase II 9

10 Meiosis I - Prophase 1. Chromosomes condense 2. Nuclear envelope dissolves 3. Centrioles move apart 4. Spindle apparatus forms 5. Synapsis - Homologous chromosomes pair up Meiosis I: Prophase: Synapsis and Crossover Synapsis Crossover Homologous Chromosomes after crossover Animation Meiosis I - Metaphase 1. Homologous chromosomes align in an equatorial plane Meiosis I - Anaphase 1. Homologous chromosomes separate 2. Reduction division of chromosomes where 2N 1N 10

11 Meiosis I - Telophase 1. Chromosomes decondense 2. Nuclear membrane forms 3. Spindle apparatus disappears Figure 8.14 The stages of meiosis MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Centrosomes Crossing over Sister chromatids Spindle 4. Cytokinesis Two haploid daughter cells form Haploid Daughter Cells Chromatin Sister chromatids Homologous chromosomes pair up Homologous chromosomes separate Figure 8.14 The stages of meiosis Meiosis - Summary MEIOSIS II: Chromatids separate TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II AND CYTOKINESIS Sister chromatids separate Haploid daughter cells form 11

12 Figure 8.15 Comparison of mitosis and meiosis Nondisjunction in meiosis I MITOSIS MEIOSIS Parent cell (before chromosome replication) MEIOSIS I Prophase Duplicated chromosome (two sister chromatids) Chromosome replication 2n = 4 Chromosome replication Prophase I Tetrad formed by synapsis of homologous chromosomes Nondisjunction in meiosis I Metaphase Chromosomes align at the metaphase plate Tetrads align at the metaphase plate Metaphase I Normal meiosis II Anaphase Telophase Sister chromatids separate during anaphase Homologous chromosomes separate during anaphase I; sister chromatids remain together Daughter cells of meiosis I Anaphase I Telophase I Haploid n = 2 Gametes 2n Daughter cells of mitosis 2n No further chromosomal replication; sister chromatids separate during anaphase II MEIOSIS II n n n n Daughter cells of meiosis II n + 1 n + 1 n 1 n 1 Number of chromosomes Fertilization after Nondisjunction Egg cell n + 1 Nondisjunction - Down syndrome = Trisomy Most common birth defect 2. 1 in Physical features Round face Flattened nose bridge Short stature Heart defects 4. Susceptibility to infections Sperm cell n (normal) Zygote 2n

13 Figure 8.20C Maternal age and incidence of Down syndrome Infants with Down syndrome (per 1,000 births) Age of mother Sex Chromosome Disorders: Klinefelter syndrome (XXY) Poor beard growth Breast Development Under-developed testes Gamete from Male Parent XY XXY Gamete from Female Parent X Sex Chromosome Disorders: Turner syndrome (XO) Independent Assortment of chromosomes at metaphase I Web of skin Constriction of aorta Gamete from Male Parent O Gamete from Female Parent X Possibility 1 Two equally probable arrangements of chromosomes at metaphase I Possibility 2 Poor breast development XO Metaphase II Underdeveloped ovaries Short stature 99% die before birth Normal Intelligence Gametes Combination 1 Combination 2 Combination 3 Combination 4 13

14 Comparing Mitosis and Meiosis END Meiosis 14