CELL DIVISION IN EUKARYOTES Professor Andrea Garrison Biology 11 Illustrations 2010 Pearson Education, Inc.
PURPOSE: Reproduction of new cells from previously existing cells 2
of Genetically Identical Cells 3
of Genetically Identical Cells 4
of Genetically Different Cells Functions of Production of eggs and sperm for sexual reproduction 5
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 6
Nucleus Preps for 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 7
Mitosis keeps chromosome number the same Meiosis cuts chromosome number in half 8
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) 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) 10
Mitosis Genetic information is coded in the chromosomes Different species have different # of chromosomes 11
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Human Chromosomes 13
Chromosome 14
Chromosome 15
Chromosome 16
Chromosome 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 18
Somatic Cell (Life) Cycle 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 20
Interphase DNA replicates inside nucleus Centrioles double 21
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Chromosomes coil Become visible under light scope Nuclear envelope dissolves Spindle forms Mitosis -- Prophase 23
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Mitosis -- Metaphase Chromosomes line up on equatorial plane of cell Spindle microtubules attach to chromosomes 25
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Mitosis -- Anaphase Microtubules pull sister chromatids apart Daughter chromosomes move towards opposite poles 27
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Mitosis -- Telophase Chromosomes reach opposite poles, uncoil Nuclear envelope reforms 29
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Cytokinesis Dividing of cell into two cells Not part of mitosis Occurs towards end of mitosis 31
Cytokinesis 32
Mitosis and Cytokinesis in Plant Cells 33
Cancer Mitosis Out of Control 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 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 36
Human Chromosomes 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 38
Meiosis Takes cell with two homologs for each chromosomes and cuts it to one homolog for each chromosome 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 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 41
Crossing Over 42
Meiosis Two sets of divisions Meiosis I and Meiosis II Meiosis I separates homologs Meiosis II separates sister chromatids 43
Meiosis Meiosis I Prophase I Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II 44
Meiosis Interphase Prior to meiosis I Chromosomes replicated 45
Meiosis I 46
Meiosis I 47
Meiosis II 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 49
Meiosis Mistakes 50
Fertilization after Nondisjunction 51
Trisomy 21 Karyotype 52
Normal Human Karyotype 53
Trisomy 21 54