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CELL DIVISION IN EUKARYOTES Professor Andrea Garrison Biology 11 Illustrations ©2010 Pearson Education, Inc. Cell Division PURPOSE: Reproduction of new cells from previously existing cells Cell Division 2 Cell Division of Genetically Identical Cells Cell Division 3 Cell Division of Genetically Identical Cells Cell Division 4 Cell Division of Genetically Different Cells Functions of Cell Division Production of eggs and sperm for sexual reproduction Cell Division 5 Cell Division • When cell divides: – Membrane pinches in two (cytokinesis) – Cytoplasm with organelles is divided roughly into two halves – Only one nucleus & important to have all genetic info • Chromosomes must replicate • Chromosomes must be divided into two nuclei – Requires very organized process Cell Division 6 Nucleus Preps for Cell Division DNA Replicates, then: Nuclear preparations for cell division of genetically identical cells Mitosis differs from Nuclear preparations for cell division of genetically different cells Meiosis Cell Division 7 Cell Division • Mitosis keeps chromosome number the same • Meiosis cuts chromosome number in half Cell Division 8 Cell Division • Both mitosis and meiosis occur in the human body • Mitosis occurs in somatic cells – Body cells that do not give rise to eggs or sperm • Meiosis occurs in germ cells – Cells in ovaries or testes that give rise to eggs or sperm (gametes) Cell Division 9 Mitosis • Occurs during cell division of somatic cells • Division of two sets of genetic material • Insures that both daughter cells have identical copies of all the mother cell’s chromosomes (full set of genetic info; one from each parent = diploid) Cell Division 10 Mitosis • Genetic information is coded in the chromosomes • Different species have different # of chromosomes Cell Division 11 Cell Division 12 Human Chromosomes Cell Division 13 Chromosome Cell Division 14 Chromosome Cell Division 15 Chromosome Cell Division 16 Chromosome Cell Division 17 Somatic Cell Cycle • 5 phases in life cycle; 4 are part of mitosis – Interphase – Prophase – Metaphase These 4 phases = mitosis – Anaphase – Telophase –I P M A T Cell Division 18 Somatic Cell (Life) Cycle Cell Division 19 Somatic Cell Cycle • Interphase – DNA is replicating, preparing for mitosis – G1, S, G2 • 4 phases of mitosis then separate the 2 sets of DNA in an organized manner Cell Division 20 Interphase • DNA replicates inside nucleus • Centrioles double Cell Division 21 Cell Division 22 Mitosis -- Prophase • Chromosomes coil – Become visible under light scope • Nuclear envelope dissolves • Spindle forms Cell Division 23 Cell Division 24 Mitosis -- Metaphase • Chromosomes line up on equatorial plane of cell • Spindle microtubules attach to chromosomes Cell Division 25 Cell Division 26 Mitosis -- Anaphase • Microtubules pull sister chromatids apart • Daughter chromosomes move towards opposite poles Cell Division 27 Cell Division 28 Mitosis -- Telophase • Chromosomes reach opposite poles, uncoil • Nuclear envelope reforms Cell Division 29 Cell Division 30 Cytokinesis • Dividing of cell into two cells • Not part of mitosis • Occurs towards end of mitosis Cell Division 31 Cytokinesis Cell Division 32 Mitosis and Cytokinesis in Plant Cells Cell Division 33 Cancer – Mitosis Out of Control Cell Division 34 Meiosis • Occurs during cell division of germ cells to produce gametes • Division of two sets of genetic material twice – Replicate once, divide twice • Produces gametes with ½ the genetic info – One of every chromosome – Fertilization will double the chromosomes Cell Division 35 Meiosis • Humans have 23 different types of chromosomes – #1 – 23 – Two of each type homologs – Each type carries genes for specific traits • Eye color, hair color, etc – Each homolog carries the specific code from one parent • Blue eyes, brown hair, etc Cell Division 36 Human Chromosomes Cell Division 37 What is a “set” of genetic info? • Somatic cells have two (homologs) of every chromosome = diploid (2n) – Human somatic cells have 46 chromosomes • Gametes have one (homolog) of every chromosome = haploid (1n) – Human gametes have 23 chromosomes Cell Division 38 Meiosis Takes cell with two homologs for each chromosomes and cuts it to one homolog for each chromosome Cell Division 39 Meiosis • Similar to mitosis except – Single cell undergoes two sets of divisions – 4 resulting cells are haploid – Chromosomes contain new gene combinations due to crossing over Cell Division 40 Meiosis What’s crossing over? – Process by which homologs switch pieces of DNA so each resulting homolog has material from each of the two initial homologs Cell Division 41 Crossing Over Cell Division 42 Meiosis • Two sets of divisions – Meiosis I and Meiosis II – Meiosis I separates homologs – Meiosis II separates sister chromatids Cell Division 43 Meiosis Meiosis I • • • • Prophase I Metaphase I Anaphase I Telophase I Meiosis II • • • • Cell Division Prophase II Metaphase II Anaphase II Telophase II 44 Meiosis • Interphase – Prior to meiosis I – Chromosomes replicated Cell Division 45 Meiosis I Cell Division 46 Meiosis I Cell Division 47 Meiosis II Cell Division 48 Meiosis • Result of meiosis is 4 haploid cells – NOT genetically identical • Formation of sperm exactly as shown • Formation of ova (eggs) – Three disintegrate – One egg (larger than rest) survives to be released each month Cell Division 49 Meiosis Mistakes Cell Division 50 Fertilization after Nondisjunction Cell Division 51 Cell Division 52 Trisomy 21 Karyotype Normal Human Karyotype Cell Division 53 Trisomy 21 Cell Division 54