CELL DIVISION IN EUKARYOTES. Professor Andrea Garrison Biology 11 Illustrations 2010 Pearson Education, Inc.

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1 CELL DIVISION IN EUKARYOTES Professor Andrea Garrison Biology 11 Illustrations 2010 Pearson Education, Inc.

2 PURPOSE: Reproduction of new cells from previously existing cells 2

3 of Genetically Identical Cells 3

4 of Genetically Identical Cells 4

5 of Genetically Different Cells Functions of Production of eggs and sperm for sexual reproduction 5

6 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

7 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

8 Mitosis keeps chromosome number the same Meiosis cuts chromosome number in half 8

9 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

10 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

11 Mitosis Genetic information is coded in the chromosomes Different species have different # of chromosomes 11

12 12

13 Human Chromosomes 13

14 Chromosome 14

15 Chromosome 15

16 Chromosome 16

17 Chromosome 17

18 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

19 Somatic Cell (Life) Cycle 19

20 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

21 Interphase DNA replicates inside nucleus Centrioles double 21

22 22

23 Chromosomes coil Become visible under light scope Nuclear envelope dissolves Spindle forms Mitosis -- Prophase 23

24 24

25 Mitosis -- Metaphase Chromosomes line up on equatorial plane of cell Spindle microtubules attach to chromosomes 25

26 26

27 Mitosis -- Anaphase Microtubules pull sister chromatids apart Daughter chromosomes move towards opposite poles 27

28 28

29 Mitosis -- Telophase Chromosomes reach opposite poles, uncoil Nuclear envelope reforms 29

30 30

31 Cytokinesis Dividing of cell into two cells Not part of mitosis Occurs towards end of mitosis 31

32 Cytokinesis 32

33 Mitosis and Cytokinesis in Plant Cells 33

34 Cancer Mitosis Out of Control 34

35 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

36 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

37 Human Chromosomes 37

38 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

39 Meiosis Takes cell with two homologs for each chromosomes and cuts it to one homolog for each chromosome 39

40 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

41 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

42 Crossing Over 42

43 Meiosis Two sets of divisions Meiosis I and Meiosis II Meiosis I separates homologs Meiosis II separates sister chromatids 43

44 Meiosis Meiosis I Prophase I Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II 44

45 Meiosis Interphase Prior to meiosis I Chromosomes replicated 45

46 Meiosis I 46

47 Meiosis I 47

48 Meiosis II 48

49 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

50 Meiosis Mistakes 50

51 Fertilization after Nondisjunction 51

52 Trisomy 21 Karyotype 52

53 Normal Human Karyotype 53

54 Trisomy 21 54