Cell reproduction occurs through mitosis and meiosis. Mitosis produces identical daughter cells and occurs in somatic cells for growth and repair. Meiosis reduces the chromosome number by half and produces gametes involved in sexual reproduction, where the union of male and female gametes leads to fertilization and the formation of a new individual with a mix of genetic material.

1. Cell Reproduction Mitosis & Meiosis

2. Why Cells Divide Surface Area/ Volume Ratio As the cell grows, the volume increases at a greater rate than the surface area Can't take in enough nutrients, or remove wastes Therefore the cell must grow or divide Growth and Repair Replace worn or damaged cells Frequency of replacement varies: bacteria ~ every 20 minutes human cells ~ every 18-22 hours Many cells in the body don't divide

3. Cell Division

4. Cellular Reproduction When the parent cell divides, it forms new daughter cells Organisms reproduce in two ways: Asexual Reproduction Sexual Reproduction

5. Sexual vs. Asexual Reproduction Asexual Reproduction production of offspring from one parent therefore genetic material is identical to parent Sexual Reproduction formation of a new individual from the union of 2 cells 2 parents, therefore offspring have some hereditary material from each

6. Types of Asexual Reproduction Binary Fission simplest form; the cell splits in 2 Spore Formation Begins with replication Spores can remain inactive until conditions are favorable molds, fungi Yeast reproduce by budding Vegetative Propagation Some plants, e.g. strawberries Regeneration planaria, star fish, etc.

7. Cell Division in Prokaryotes Binary Fission: The simplest form of cell division The cell splits in 2

8. The Process of Binary Fission First the single circular chromosome duplicates = Replication Both chromosomes attach to sites on the cell membrane As the cell grows, a new membrane forms between attachment sites Membrane pinches off and the new cells separate

9. Sexual Reproduction The joining of 2 specialized sex cells called gametes male = sperm female = ovum Process of combining gametes = fertilization Fertilization produces a zygote has characteristics of both parents

10. Human Sexual Reproduction Male testis produces sperm Female ovary produces ova Each has 23 chromosomes Unite to form a zygote with 46 chromosomes 23 pair Develops into a fetus

11. Cell Division All types of reproduction require cell division 2 processes can be used to divide the cell’s nuclear material: Mitosis Occurs in somatic cells (body cells) in eukaryotes As a result of mitosis each daughter cell receives an exact copy of the chromosomes present in the parent cell Meiosis Occurs in gametes (sex cells) As a result each daughter cell receives 1 of each pair of chromosomes present in the parent cell

12. Mitosis Cell division in eukaryotic cells involves nuclear division called mitosis Occurs in somatic cells body cells; not sex cells As a result of mitosis, each daughter cell receives an exact copy of the chromosomes present in the parent cell Chromosomes contain genetic material DNA

13. Chromosomes During cell division in eukaryotic cells, the DNA is coiled into chromosomes Every body cell of the same type of organism has the same number of chromosomes humans = 46 goldfish = 94 mosquito = 6

14. Chromosome Structure Each chromosome is formed from two joined strands called chromatids Each chromatid is alike has a long arm & a short arm joined at the centromere Chromosomes contain DNA and associated proreins

15. Chromosomal Proteins Each chromosome is a single DNA molecule and associated proteins Histones – One type of chromosomal protein The DNA wraps tightly around the histones Histones help maintain the shape of the chromosome Nonhistone proteins - control the activity of specific regions of DNA

16. Picturing Chromosome Structure

17. Visualizing Chromosomes

18. Chromosome Make-up Chromosomes of somatic cells are in pairs One of each pair comes from mother, one from father The 2 chromosomes in a pair are homologous Alike in appearance and type of genetic information carried Humans have 23 pairs of chromosomes 22 pairs of autosomes Autosomes are all but the sex 2 sex chromosomes ( X & Y)

19. Sex Chromosomes Determine the sex of the organism Also carry other genetic information In humans, either X or Y Females are XX, males are XY Thus the male determines the sex of the offspring

20. Haploid vs. Diploid Cells with two copies of each chromosome = diploid Autosomal cells are diploid Gametes (sex cells) have only one of each type of chromosome Cells with one copy of each chromosome = haploid

21. Karyotypes A picture of paired human chromosomes Used to to detect certain genetic diseases

23. Mitosis The process of dividing the nuclear material in a somatic cell in eukaryotes Necessary for cell division

24. Preparation for Mitosis Interphase The time between the formation of a cell through mitosis and the next mitosis Most of the cell cycle is interphase During this phase cell prepares by: replicating genetic material producing organelles assembling structures needed for mitosis

25. Chromosomes & Interphase During interphase chromosomes cannot be distinguished under the light microscope They appear as chromatin At the start of mitosis, the chromatin thickens, and chromosomes become visible

26. The Cell Cycle The sequence of cell growth and division The cell cycle can last several hours to several days Can be affected by environmental factors, like temperature Has 4 stages: mitosis & division of cytoplasm ( cytokinesis ) The other 3 are part of interphase : G1 S G2

27. Picturing the Cell Cycle

28. G1 - Growth After mitosis, a period of intense cellular activity and growth The cell doubles in size Enzyme production is high Cells that stop growing remain in G1

29. S- Synthesis Cells that divide enter S, or synthesis, phase The chromosomes replicate

30. G2 – Further Growth A second period of growth Structures used in mitosis are assembled

31. The Phases of Mitosis Mitosis is actually a continuous process But we divide it into 4 phases: Prophase Metaphase Anaphase Telophase

32. Prophase 60% of the period of mitosis is prophase Divided into 3 parts: early, middle, & late Chromosomes begin to coil into short rods Nucleoli break down & begin to disappear 2 pairs of dark spots called centrosomes appear outside the nuclear membrane In animal cells, the centrosomes contain centrioles , formed from microtubules Plant cells have no centrioles The centrosomes move to opposite sides of the cell

33. Mid Prophase At the beginning of mid-prophase spindle fibers form between the centrioles Additional fibers radiating out from each centriole form the aster The nuclear membrane has broken down and disappeared

34. The Mitotic Spindle Spindle fibers made of microtubules radiate from the centrosomes This array of spindle fibers = the mitotic spindle 2 types of spindle fibers: Kinetechore fibers Attach to a disk-shaped protein called a kinetecore Found in the centromere of each chromosome Extend from the kinetechore of each chromatid to one of the centrosomes Polar fibers Extend across the dividing cell from one centrosome to the other

36. Late Prophase The centrosome pairs are at opposite ends of the cell The centosomes are fully formed Chromosomes are attached to the centrosomes by spindle fibers Other spindle fibers stretch across the cell from one centriole to the other

38. Metaphase The chromosomes are pushed and pulled by spindle fibers along cell's the midplane called the equator

39. Anaphase Begins with the separation of chromatids in each chromosome Spindle fibers appear to shorten, pulling the chromatids apart at the centomere Each chromatid is now a chromosome 2 sets of separated chromosomes then move through the cytoplasm to opposite poles of the cell

41. Telophase The last stage of mitosis After the individual chromosomes have reached opposite poles of the cell, spindles disappear A nuclear membrane forms around each set of chromosomes Chromosomes return to a thread-like mass Centrioles duplicate 2 centrioles formed in each daughter cell Nucleoli re-form within each newly formed nucleus

43. Cytokinesis The division of the cytoplasm Follows mitosis Cytokinesis begins during telophase In animal cells, the cell membrane pinches together The area that pinches in and separates is called the cleavage furrow In plants, a cell plate is formed, dividing the two halves

44. Picturing Cytokinesis

47. Chromosome Number Cells formed thru mitosis have the same number of chromosomes as the parent cells If combined in sexual reproduction, the offspring would have 2x chromosomes! Therefore gametes have only half the number of chromosomes of somatic cells Gametes = sex cells

48. Meiosis Gametes need another process for nuclear division Meiosis reduces the number of chromosomes to 1/2 the number in somatic cells

49. Meiosis I & II Forming haploid daughter cells from diploid parent cells requires two successive cell divisions: First = Meiosis I – homologous chromosomes separate Second = Meiosis II chromatids of each chromosome separate

50. Meiosis I Preceded by replication of DNA that forms the chromosome Synapsis = pairing of homologous chromosomes Each pair of homologous chromosomes twists around each other, forming a structure called a tetrad Meiosis can be divided into same 4 phases as mitosis: Prophase, Metaphase, Anaphase, Telophase

51. Prophase I Chromatin begins to coil into short rods Homologous chromosomes are formed Spindle fibers appear Nucleoli break down By the end, the nuclear membrane has dissolved, and tetrads are visible

52. Crossing Over During synapsis , (prophase I) the chromatids of homologous pairs twist around each other A portion of one chromatid may break off and reattach, “trading” with the same piece from its homologous partner The exchange of genes by reciprocal segments of homologous chromosomes during meiosis = “ crossing-over ”

53. Crossing over causes exchange of genetic material between maternal & paternal chromosomes Results in genetic recombination Genetic recombination is less likely in genes that are closer together.

54. Chromosome Mapping The likelihood that recombination will occur due to crossing-over depends on the genes’ distance from each other on the chromosome Scientists can determine how frequently genes for particular traits occur together in offspring This can be used to create a map of the chromosome 1% recombination (crossing-over) = 1 map unit

55. Metaphase I Tetrads line up along the equator of the cell Each tetrad becomes attached to spindle fibers

56. Anaphase I Homologous chromosomes that form each tetrad are pulled apart in pairs One pair goes to one end of the cell, the other to opposite end

57. Telophase I Chromosomes reach ends of the cell Cell divides into 2 daughter cells

59. Independent Assortment During Anaphase I, one member of each homologous chromosome pair moves to one end of the cell, the other moves to the opposite end The separation of homologous chromosomes is random More, or fewer maternal (or paternal) chromosomes may end up on one side or the other Each separation is independent of the others This is the principal of independent assortment of chromosomes Results in genetic variation

61. Meiosis I Summary Meiosis I is a Reductive Division It reduces the number of chromosomes from diploid "2n" to haploid "n"

62. Meiosis II Similar to mitosis but not preceded by replication of DNA 4 Stages: Prophase II Metaphase II Anaphase II Telophase II

63. Prophase II & Metaphase II Prophase II A new spindle forms around paired chromatids Metaphase II Chromosomes line up along the equator They are attached at the centromere to spindle fibers

64. Anaphase II Centromeres duplicate & the chromatids separate Resulting single chromatids move to opposite poles Chromatids are now called chromosomes

65. Telophase II A nuclear membrane forms around each set of chromosomes The spindle breaks down and cytokinesis occurs Result: 4 haploid daughter cells

67. Males vs. Females In males, all 4 daughter cells differentiate to become sperm In females, the cytoplasm divides unevenly in Meiosis I The smaller cell = first polar body doesn't survive In Meiosis II, the division is again unequal smaller half is second polar body So only 1 of 4 daughter cells survives rich in cytoplasm, has many nutrients to nourish the young organism

68. Comparing Mitosis & Meiosis MEIOSIS 2 4 diploid haploid different MITOSIS 1 2 diploid diploid identical # of nuclear divisions: # of daughter cells: Parent cell type: Daughter cell type: Genetic likeness to parent:

70. Control of Cell Division Timing and rate of cell division varies in different cell types Control of rate of division is critical Some cells require regulatory substances to begin division = growth factors

71. Effect of Growth Factors

72. Effect of Density Density of cells also effects the rate of division Crowding inhibits cell division

73. The Restriction Point A crucial checkpoint occurs late in the G1 phase of the cell cycle Point of decision to divide = restriction point Cell cannot turn back after this point If it is “yes,” cell goes to S phase and copies DNA If “no,” it goes to non-dividing state (G 0 ) Most cells are in G 0

74. MPF After S, the cell will enter G2 The “OK” signal that causes the cell to proceed from G2 to mitosis = mitosis promoting factor (MPF) A complex of proteins MPF is an enzyme Protein kinase

75. Abnormal Cell Division Cancer cells do not respond normally to the body’s control mechanisms for cell division Cancer cells divide excessively Can invade other body tissues When a cell divides abnormally = transformed Abnormal cells are usually destroyed by the immune system

76. Cancer If abnormal cells are not destroyed and reproduce, they may form a mass of abnormal cells = tumor Benign tumor = abnormal cells remain at the original site Malignant tumor = cells spread to other parts of the body Metastasis = spread of cancer cells in the body

77. Breast Cancer Cell