Reproduction and Inheritance: Sexual vs Asexual

1. 0 Chapter 8 The Cellular Basis of Reproduction and Inheritance

2. How are the offspring of sexual reproduction different from the offspring of asexual reproduction? • Is it more beneficial for an endangered species to reproduce sexually or asexually? Do Now

3. Rain Forest Rescue Scientists in Hawaii Have attempted to “rescue” endangered species from extinction

4. The goals of these scientists were To promote reproduction to produce more individuals of specific endangered plants Kauai, Hawaii Cyanea kuhihewa

5. What does a nucleic acid do? • Store genetic information • Make proteins • Control cellular activities • What is a nucleotide? • The monomers of nucleic acids • What organelle is directly involved in cell division? • Nucleus Do Now

6. In sexual reproduction Fertilization of sperm and egg produces offspring In asexual reproduction The creation of offspring carrying genetic information from just a single parent

7. CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION 8.1 Like begets like, more or less Some organisms reproduce asexually And their offspring are genetic copies of the parent and of each other LM 340 Figure 8.1A

8. Other organisms reproduce sexually Creating a variety of offspring Sexual reproduction is more likely to increase genetic variation than is asexual reproduction. Figure 8.1B

9. With the exception of identical twins, siblings who have the same two biological parents are likely to look similar, but not identical, to each other because they have similar but not identical combination of genes.

10. 8.2 Cells arise only from preexisting cells Cell division is at the heart of the reproduction of cells and organisms Because cells come only from preexisting cells

11. Prokaryotic chromosomes 8.3 Prokaryotes reproduce by binary fission Prokaryotic cells reproduce asexually by binary fission. http://www.youtube.com/watch?v=K0ZP8VtxUZ0 Colorized TEM 32,500 Figure 8.3B

12. Plasmamembrane Prokaryoticchromosome Cell wall Duplication of chromosomeand separation of copies 1 Continued elongation of thecell and movement of copies 2 As the cell replicates its single chromosome, the copies move apart And the growing membrane then divides the cells Division intotwo daughter cells 3 Figure 8.3A

13. THE EUKARYOTIC CELL CYCLE AND MITOSIS 8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division A eukaryotic cell has many more genes than a prokaryotic cell And they are grouped into multiple chromosomes in the nucleus

14. Individual chromosomescontain a very long DNA molecule associated with proteins. The proteins help maintain the structure of chromosomes and control the activity of genes The chromosomes are visible only when the cell is in the process of dividing. If a cell is not undergoing division Chromosomes occur in the form of thin, loosely packed chromatin fibers LM 600 Figure 8.4A

15. Figure 2: Different levels of DNA condensation. • Single DNA strand. • Chromatin strand (DNA with histones). • Condensed chromatin during interphase with centromere. • Condensed chromatin during prophase. (Two copies of the DNA molecule are now present) • Chromosome during metaphase.

16. Sister chromatids Before a cell starts dividing, the chromosomes replicate Producing identical structures called sister chromatids joined together at the centromere Centromere TEM 36,000 Figure 8.4B

17. Chromosomeduplication Sisterchromatids Centromere Cell division involves the separation of sister chromatids And results in two daughter cells, each containing a complete and identical set of chromosomes Chromosomedistributiontodaughtercells Figure 8.4C

18. INTERPHASE G1 S(DNA synthesis) 8.5 The cell cycle multiplies cells The cell cycle consists of two major phases Cell Cycle G2 Mitosis Cytokinesis MITOTICPHASE (M) Figure 8.5

19. During interphase Chromosomes duplicate and cell parts are made Eukaryotes spend most of their time in interphase. Consists of 3 Phases: G1Phase-cell grows SPhase-DNA is replicated G2Phase-cell grows more as it completes preparation for cell division.

20. During the mitoticphase Duplicated chromosomes are evenly distributed into two daughter nuclei Consists of two phases: Mitosis- the nucleus and its contents, including the duplicated chromosomes, divide and are evenly distributed to form 2 daughter nuclei. Cytokinesis- The process by which the cytoplasm of a eukaryotic cell divides to produce two cells

21. 8.6 Cell division is a continuum of dynamic changes In mitosis, after the chromosomes coil up A mitotic spindle moves them to the middle of the cell

22. The sister chromatids then separate And move to opposite poles of the cell, where two nuclei form Cytokinesis, in which the cell divides in two Overlaps the end of mitosis

23. Interphase G1-offspring cells grow to mature size S Phase-the cell’s DNA is copied (synthesized) G2-represents the time gap following DNA synthesis and preceding cell division; RNA is copied. G0-cells do not copy their DNA and do not prepare for cell division.

24. Prophase Chromatin fibers become more tightly coiled and folded, forming chromosomes The nuclear envelope fragments and the nucleoli disappear Each duplicated chromosome appears as two identical sister chromatids. The mitotic spindle begins to form

25. Prometaphase Microtubules emerging from the centrosomes at the poles of the spindle reach the chromosomes. Kinetochore attaches to sister chromatid & to the spindle fibers.

26. Metaphase Mitotic spindle is fully formed, with its poles at opposite ends of the cell. The chromosomes line up on a plane located equidistant from the two spindle poles. The kinetochores of the 2 sister chromatids face opposite poles of the spindle.

27. Anaphase Sister chromatids separate. Daughter chromosomes begin to move toward opposite poles of the cell.

28. Telophase Cell elongation continues. The nuclear envelope re-forms and the nucleoli reappears. At the end, the mitotic spindle disappears.

29. Cytokinesis Division of the cytoplasm Usually occurs along with telophase Mitosis Overview

30. LM 250 INTERPHASE PROPHASE PROMETAPHASE Centrosomes(with centriole pairs) Fragmentsof nuclearenvelope Centrosome Early mitoticspindle Kinetochore Chromatin The stages of cell division Nucleolus Centromere Chromosome, consistingot two sister chromatids Spindlemicrotubules Nuclearenvelope Plasmamembrane Figure 8.6 (Part 1)

31. TELOPHASE AND CYTOKINESIS ANAPHASE METAPHASE Nucleolusforming Cleavagefurrow Metaphaseplate Daughterchromosomes Nuclearenvelopeforming Spindle Figure 8.6 (Part 2)

32. Cleavagefurrow SEM 140 8.7 Cytokinesis differs for plant and animal cells In animals Cytokinesis occurs by a constriction of the cell (cleavagefurrow) Cleavage furrow Contracting ring ofmicrofilaments Daughter cells Figure 8.7A

33. Daughternucleus Cell plateforming Wall ofparent cell TEM 7,500 In plants A membranous cellplate splits the cell in two Plant cell division must maintain the integrity of the cell wall. Cell wall New cell wall Vesicles containingcell wall material Cell plate Daughter cells Figure 8.7B

34. 8.8 Anchorage, cell density, and chemical growth factors affect cell division Most animal cells divide Only when stimulated, and some not at all In order for a plant or animal to grow and develop normally it must be able to control the timing and rate of cell division in different parts of its body.

35. Cells anchor todish surfaceand divide. When cells haveformed a completesingle layer, theystop dividing (density-dependent inhibition). Anchorage Dependence-Most normal cells divide only when attached to a surface Density-Dependent Inhibition-They continue dividing until they touch one another If some cells arescraped away, theremaining cells divideto fill the dish with asingle layer and thenstop (density-dependentinhibition). Figure 8.8A

36. Growth factors Are proteins secreted by cells that stimulate other cells to divide An inadequate supply causes density-dependent inhibition. After forming asingle layer,cells havestopped dividing. Providing anadditional supply ofgrowth factorsstimulatesfurther cell division. Figure 8.8B

37. 8.9 Growth factors signal the cell cycle control system A set of proteins within the cell Controls the cell cycle Receives messages from outside of the cell that influence cell division. Triggers and controls major events in the cell cycle. Is influenced by growth factors that bind to cell receptors. Includes three key checkpoints to complete a cell cycle.

38. G1 checkpoint G0 Signals affecting critical checkpoints in the cell cycle Determine whether a cell will go through the complete cycle and divide Controlsystem S G1 G2 M M checkpoint G2 checkpoint Figure 8.9A

39. Growth factor Plasma membrane Relayproteins The binding of growth factors to specific receptors on the plasma membrane Is usually necessary for cell division. Receptorprotein G1 checkpoint Signaltransductionpathway Controlsystem S G1 M G2 Figure 8.9B

40. CONNECTION 8.10 Growing out of control, cancer cells produces malignant tumors Mature human nerve cells and muscle cells are permanently in a state of nondivision.   Cancer cells divide excessively to form masses called tumors Cancer is not usually inherited because  the chromosomal changes in cancer are usually confined to somatic cells.

41. Benign Tumor-Abnormal cells remain at the original site Malignant tumors-invade other tissues. Metastasis-the spread of cancer cells via the circulatory system beyond their original site. Lymphvessels Tumor Bloodvessel Glandulartissue Cancer cells invadeneighboring tissue. Cancer cells spread throughlymph and blood vessels toother parts of the body. A tumor grows from asingle cancer cell. Figure 8.10

42. Radiation and chemotherapy Are effective as cancer treatments because they interfere with cell division by preventing the mitotic spindle from forming Cancer Cells

43. Do Now A typical human cell contains 46 chromosomes. After mitosis and cytokinesis, each of the two new cells formed from the original cell has ___ chromosomes. Complete set of 46 chromosomes.

44. 8.11 Review of the functions of mitosis: Growth, cell replacement, and asexual reproduction When the cell cycle operates normally, mitotic cell division functions in growth LM 500 Figure 8.11A

45. Replacement of damaged or lost cells or tissues LM 700 Figure 8.11B

46. Asexual reproduction LM 10 Figure 8.11C

47. MEIOSIS AND CROSSING OVER 8.12 Chromosomes are matched in homologous pairs The somatic (body) cells of each species Contain a specific number of chromosomes For example human cells have 46 Making up 23 pairs of homologous chromosomes

48. Chromosomes The chromosomes of a homologous pair Carry genes for the same characteristics at the same place, or locus Centromere Figure 8.12 Sister chromatids

49. 8.13 Gametes have a single set of chromosomes Cells with two sets of chromosomes Are said to be diploid Gametes, eggs and sperm, are haploid With a single set of chromosomes

50. Haploid gametes (n = 23) n Egg cell n Sperm cell Meiosis Fertilization Diploidzygote(2n = 46) Sexual life cycles Involve the alternation ofhaploid and diploid stages 2n Multicellulardiploid adults(2n = 46) Mitosis and development Figure 8.13