1. CHAPTER 8 The Cellular Basis of REPRODUCTION

2. CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION Copyright © 2009 Pearson Education, Inc.

3. 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 –Involves MITOSIS (Eukaryotic Organisms); BINARY FISSION (Prokaryotic Organisms) –CLONING is an asexual process –Sexual reproduction –Offspring are similar to parents, but show variations in traits –Involves inheritance of unique sets of genes from two parents –Involves MEIOSIS Copyright © 2009 Pearson Education, Inc.

4. Cells arise only from preexisting cells – Cell division perpetuates life –Cell division is the reproduction of cells –Cells are composed of : Carbohydrates, Lipids, Proteins, Nucleic Acids, so cell division requires the building of these molecules from their monomers –Is cell division an ENDERGONIC or EXERGONIC process? What does it require? Copyright © 2009 Pearson Education, Inc.

5. –Roles of cell division –Asexual reproduction –Reproduction of an entire single-celled organism (MITOSIS or BINARY FISSION) –Growth of a multicellular organism (MITOSIS) –Growth from a fertilized egg into an adult (MITOSIS) –Repair and replacement of cells in an adult (MITOSIS) –Sexual reproduction –Sperm and egg production (MEIOSIS) Cells arise only from preexisting cells Copyright © 2009 Pearson Education, Inc.

6. – Binary fission means “dividing in half” –Occurs in prokaryotic cells –Two identical cells arise from one cell –Steps in the process –A single circular chromosome duplicates, and the copies begin to separate from each other –The cell elongates, and the chromosomal copies separate further –The plasma membrane grows inward at the midpoint to divide the cells Prokaryotes reproduce by binary fission Copyright © 2009 Pearson Education, Inc.

7. Prokaryotic chromosome Duplication of chromosome and separation of copies Cell wall Plasma membrane 1

8. Prokaryotic chromosome Duplication of chromosome and separation of copies Cell wall Plasma membrane 1 Continued elongation of the cell and movement of copies 2

9. Prokaryotic chromosome Duplication of chromosome and separation of copies Cell wall Plasma membrane 1 Continued elongation of the cell and movement of copies 2 Division into two daughter cells 3

10. Prokaryotic chromosomes

11. THE EUKARYOTIC CELL CYCLE AND MITOSIS Copyright © 2009 Pearson Education, Inc.

12. – Eukaryotic chromosomes are composed of chromatin –Chromatin = DNA + proteins –To prepare for division, the chromatin becomes highly compact, and the chromosomes are visible with a microscope –Early in the division process, chromosomes duplicate –Each chromosome appears as two sister chromatids, containing identical DNA molecules –Sister chromatids are joined at the centromere, a narrow region The large, complex chromosomes of eukaryotes duplicate with each cell division Copyright © 2009 Pearson Education, Inc.

13. Centromere Chromosome duplication Sister chromatids Chromosome distribution to daughter cells

14. Sister chromatids Centromere

16. – 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 (DNA REPLICATION) –G 2 —growth, preparation for division –Mitotic phase: division –Mitosis—division of the nucleus –Cytokinesis—division of cytoplasm The Cell Cycle Copyright © 2009 Pearson Education, Inc.

17. S (DNA synthesis) G1G1 G2G2 Cytokinesis Mitosis I NTERPHASE M ITOTIC PHASE (M)

18. – Mitosis progresses through a series of stages –Prophase (Prometaphase) –Metaphase –Anaphase –Telophase – Cytokinesis overlaps telophase Cell division is a continuum of dynamic changes Copyright © 2009 Pearson Education, Inc.

19. – Before Mitosis begins: – Interphase –In the cytoplasm –Cytoplasmic contents double –New organelles are formed –In the nucleus –Chromosomes (DNA) duplicate during the S phase Cell division is a continuum of dynamic changes Copyright © 2009 Pearson Education, Inc.

20. – Prophase and Metaprophase –In the cytoplasm –Microtubules begin to emerge forming the spindle –In the nucleus –Chromosomes coil and become compact –Nuclear Membrane disappears Cell division is a continuum of dynamic changes Copyright © 2009 Pearson Education, Inc.

21. Centrosomes (with centriole pairs) Kinetochore Early mitotic spindle Chromatin INTERPHASE PROMETAPHASEPROPHASE Centrosome Fragments of nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Nuclear envelope Spindle microtubules Nucleolus Centromere

22. – Metaphase –Chromosomes align at the cell equator (middle of the cell) Cell division is a continuum of dynamic changes Copyright © 2009 Pearson Education, Inc.

23. – Anaphase –Sister chromatids separate at the centromeres and move to opposite poles of the cell Cell division is a continuum of dynamic changes Copyright © 2009 Pearson Education, Inc.

24. – Telophase –Opposite of PROPHASE –The nuclear membrane forms –Chromatin uncoils –The spindle disappears –CYTOKINESIS occurs Cell division is a continuum of dynamic changes Copyright © 2009 Pearson Education, Inc.

25. Metaphase plate Nucleolus forming METAPHASETELOPHASE AND CYTOKINESISANAPHASE Cleavage furrow Daughter chromosomes Nuclear envelope forming Spindle

26. – Cytokinesis –Cleavage in animal cells –A cleavage furrow forms from a contracting ring of microfilaments, interacting with myosin –The cleavage furrow deepens to separate the contents into two cells –Cytokinesis in plant cells –A cell plate forms in the middle from vesicles containing cell wall material –The cell plate grows outward to reach the edges, dividing the contents into two cells –Each cell has a plasma membrane and cell wall Cytokinesis differs for plant and animal cells Copyright © 2009 Pearson Education, Inc.

27. Cleavage furrow Contracting ring of microfilaments Daughter cells Cleavage furrow

28. Cell plate Daughter cells Cell wall Vesicles containing cell wall material Daughter nucleus Cell plate forming Wall of parent cell New cell wall

29. –Applying Your Knowledge Human cells have 46 chromosomes (the DIPLOID number or 2 sets) –At the end of Mitosis, how many chromosomes are in each cell? –Is the genetic material identical in each cell? Cell division is a continuum of dynamic changes Copyright © 2009 Pearson Education, Inc.

30. CLONING A somatic cell from one parent is used The nucleus of a somatic cell in put into an egg cell (ovum) that has had its nucleus removed The ovum with the somatic cell nucleus behaves like a Zygote A new eukaryotic organism is produced with the DNA of only one parent (it is a clone of the parent)

31. Remove nucleus from egg cell Implant blastocyst in surrogate mother Add somatic cell from adult donor Donor cell Remove embryonic stem cells from blastocyst and grow in culture Reproductive cloning Nucleus from donor cell Grow in culture to produce an early embryo (blastocyst) Therapeutic cloning Clone of donor is born Induce stem cells to form specialized cells

32. – Cancer cells escape controls on the cell cycle –Cancer cells divide rapidly –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 CONNECTION: Growing out of control, cancer cells produce malignant tumors Copyright © 2009 Pearson Education, Inc.

33. Mitosis produces genetically identical cells for –Growth –Replacement –Asexual reproduction Review: Mitosis provides for growth, cell replacement, and asexual reproduction Copyright © 2009 Pearson Education, Inc.

34. MEIOSIS AND CROSSING OVER Copyright © 2009 Pearson Education, Inc.

35. – Meiosis is a process that converts diploid cells into haploid cells –Diploid cells have two homologous sets (2n) of chromosomes –Haploid cells have one set (1n) of chromosomes –Meiosis occurs in the sex organs, producing gametes— sperm and eggs – Fertilization is the union of sperm and egg –The zygote formed by fertilization has a diploid chromosome number (2n), one set from each parent Gametes have a single set of chromosomes Copyright © 2009 Pearson Education, Inc.

36. – Somatic cells have pairs of homologous chromosomes, receiving one member of each pair from each parent – Homologous chromosomes are matched in –Length –Gene locations –A locus (plural, loci) is the position of a gene –Different versions of a gene may be found at the same locus on maternal and paternal chromosomes Chromosomes are matched in homologous pairs Copyright © 2009 Pearson Education, Inc.

37. Sister chromatids One duplicated chromosome Centromere Homologous pair of Chromosomes: One from Mother; One from Father

38. – Which characteristics are similar for mitosis and meiosis? –One duplication of chromosomes – Which characteristics are unique to meiosis? –Two divisions of the cells (stages I and II): 4 new cells formed instead of 2 –Pairing of homologous chromosomes during PROPHASE I and exchange of genetic material by CROSSING OVER –Homologous pairs of chromosomes line up a the cell equator during METAPHASE I –Cells formed are NOT GENETICALLY IDENTICAL Mitosis and meiosis have important similarities and differences Copyright © 2009 Pearson Education, Inc.

39. Centrosomes (with centriole pairs) PROPHASE I Microtubules attached to kinetochore INTERPHASE Sites of crossing over Metaphase plate Spindle MEIOSIS I : Homologous chromosomes separate METAPHASE I Sister chromatids remain attached ANAPHASE I Nuclear envelope Sister chromatids Centromere (with kinetochore) Homologous chromosomes separate Chromatin Tetrad

40. Separation of homologous chromosomes at anaphase I C E c e Chiasma Separation of chromatids at anaphase II and completion of meiosis CE c e cE C e ce c E C E C e Parental type of chromosome Gametes of four genetic types Recombinant chromosome Parental type of chromosome Recombinant chromosome 4 3

41. PROPHASE I MEIOSIS II : Sister chromatids separate METAPHASE II ANAPHASE II Cleavage furrow TELOPHASE II AND CYTOKINESIS Sister chromatids separate Haploid daughter cells forming TELOPHASE II AND CYTOKINESIS

42. – What is the outcome of each process? –Mitosis: two genetically identical cells, with the same chromosome number as the original cell –Meiosis: four genetically different cells, with half the chromosome number of the original cell Mitosis and meiosis have important similarities and differences Copyright © 2009 Pearson Education, Inc.

43. Prophase Metaphase I Metaphase 2n = 4 Tetrads align at the metaphase plate Duplicated chromosome (two sister chromatids) Parent cell (before chromosome duplication) Chromosome duplication Chromosomes align at the metaphase plate Anaphase Telophase Sister chromatids separate during anaphase Daughter cells of mitosis 2n2n 2n2n n Chromosome duplication Site of crossing over Tetrad formed by synapsis of homologous chromosomes M EIOSIS Prophase I Anaphase I Telophase I M ITOSIS M EIOSIS I Haploid n = 2 Daughter cells of meiosis I M EIOSIS II n nn Daughter cells of meiosis II Homologous chromosomes separate (anaphase I ); sister chroma- tids remain together No further chromosomal duplication; sister chromatids separate (anaphase II )

44. Independent orientation of chromosomes and crossing over in meiosis and random fertilization lead to varied offspring  Independent orientation at Metaphase I –Each pair of chromosomes independently aligns at the cell equator; there is an equal probability of the maternal or paternal chromosome facing a given pole –The number of combinations for chromosomes packaged into gametes is 2 n where n = haploid number of chromosomes (How many combinations for human?)  Crossing over in Prophase I (How many combinations in humans?)  Random Fertilization –The combination of each unique sperm with each unique egg increases genetic variability

45. Two equally probable arrangements of chromosomes at metaphase I Possibility 1 Possibility 2 Metaphase II Combination 1 Gametes Combination 2 Combination 3 Combination 4

46. – Nondisjunction is the failure of chromosomes or chromatids to separate during meiosis –During Meiosis I –Both members of a homologous pair go to one pole –During Meiosis II –Both sister chromatids go to one pole – Fertilization after nondisjunction yields zygotes with altered numbers of chromosomes Accidents during meiosis can alter chromosome number Copyright © 2009 Pearson Education, Inc.

47. Centromere Sister chromatids Pair of homologous chromosomes 5

48. Nondisjunction in meiosis I Normal meiosis II n + 1 Gametes Number of chromosomes n + 1n – 1

49. Nondisjunction in meiosis II Normal meiosis I Gametes Number of chromosomes n + 1n – 1n n

50. – Trisomy 21 involves the inheritance of three copies of chromosome 21 –Trisomy 21 is the most common human chromosome abnormality –An imbalance in chromosome number causes Down syndrome, which is characterized by –Characteristic facial features –Susceptibility to disease –Shortened life span –Mental retardation –Variation in characteristics –The incidence increases with the age of the mother An extra copy of chromosome 21 causes Down syndrome Copyright © 2009 Pearson Education, Inc.