1. CELL REPRODUCTION

2. 1. Recall that as the cell grows, its volume increases much more rapidly than the surface area. -Therefore when a cell reaches a size where it is no longer capable of adequately supplying the needs of each part of the cell, the cell divides.

3. 2. Cell division: a. prevents the cell from becoming too large. b. It also is the way the cell reproduces so that you grow and heal certain injuries. c. Cells reproduce by a cycle of growing and dividing called the cell cycle.

4. a. Interphase is the stage during which the cell grows, carries out cellular functions, and replicates the DNA. b.Mitosis is the stage of the cell cycle during which the cell’s nucleus and nuclear material divide. c. Cytokinesis is the method by which a cell’s cytoplasm divides, creating a new cell. 3. Outline of the Cell Cycle:

5. 4. The Stages of Interphase a. The first stage of interphase, G 1  The cell is growing, carrying out normal cell functions, and preparing to replicate DNA.

6. b. The Second Stage of Interphase, S  The cell copies its DNA in preparation for cell division.

8. c. The Third Stage of Interphase, G 2  The cell prepares for the division of its nucleus.

9. d. The fourth stage is nuclear division called mitosis. *To understand mitosis and its terminology, it is necessary to learn a bit more about DNA and chromosomes.

10. 1. THE DNA HOUSED IN THE NUCLEUS OF EACH CELL CONTROLS THE GROWTH AND DEVELOPMENT OF THE CELL. 3. IN HUMAN CELLS, THE DNA, ALONG WITH PROTEINS, IS FOUND IN LONG STRANDS CALLED CHROMOSOMES. 2. CHROMATIN- THE NAME GIVEN TO THE COMPLEX OF DNA AND PROTEIN IN THE NUCLEUS - NOT TIGHTLY COILED. 4. A TYPICAL HUMAN CELL CONTAINS 46 CHROMOSOMES. THESE 46 ARE COMPOSED OF 23 PAIRS OF CHROMOSOMES. ONE SET OF 23 ORIGINALLY CAME FROM THE MOTHER IN THE EGG AND THE OTHER 23 ORIGINALLY CAME FROM THE FATHER IN THE SPERM.

13. 5. EACH TYPE OF ORGANISM HAS A TYPICAL NUMBER OF CHROMOSOMES. IN HUMANS, THE NUMBER IS 46. THAT IS CALLED THE DIPLOID OR 2N NUMBER OF CHROMOSOMES BECAUSE IT IS 2 TIMES THE NUMBER YOU RECEIVE FROM ONE PARENT. (2 X 23 = 46) 6. 23 IS THE HAPLOID OR 1N NUMBER OF CHROMOSOMES FOR HUMANS BECAUSE IT IS THE NUMBER YOU RECEIVE FROM ONE PARENT. (1 X 23 = 23) 7. OF YOUR 46 CHROMOSOMES, 2 ARE SEX CHROMOSOMES AND THE OTHER 44 ARE AUTOSOMES. YOU RECEIVE ONE SEX CHROMOSOME FROM EACH PARENT. IF YOU RECEIVE XX YOU ARE FEMALE. IF YOU RECEIVE XY YOU ARE MALE.

15. 8. Recall that all of the Chromosomes were replicated in the S (synthesis) phase of the cell cycle. Therefore going into mitosis (nuclear division) there is a tetraploid (4n) number of chromosomes. For humans this number is 92.

16. *A pair of the same number chromosome is called a homologous pair. Ex. Both #1 chromosomes are a homologous pair.

17. 10. The sister chromatids are attached at the centromere. 9. The replicated chromosomes are called sister chromatids. They are identical! *The kinetochore is the site of attachment of spindle fibers.

19. MITOSIS

20. 1. MITOSIS- THE DIVISION OF THE NUCLEUS: -MITOSIS OCCURS AT THE END OF THE SECOND GROWTH PHASE. AT THIS POINT THE CELL HAS ALREADY REPLICATED ITS DNA AND ITS VOLUME HAS REACHED SUCH A SIZE THAT THE CELL NEEDS TO DIVIDE TO SURVIVE.

21. A.PROPHASE- THE CHROMOSOMES CONDENSE, MAKING IT EASIER FOR THEM TO MOVE ABOUT THE CELL. THE NUCLEAR MEMBRANE DISSOLVES AND SPINDLE FIBERS, MADE OF PROTEINS, BEGIN TO FORM – BRANCHING OUT FROM THE CENTRIOLES AT EITHER POLE OF THE CELL.

24. b. Metaphase- The chromosomes, attached to the spindle fibers at the kinetochore, align along the equator of the cell.

25. C. ANAPHASE- IDENTICAL COPIES OF CHROMOSOMES ARE SEPARATED AND PULLED TOWARDS OPPOSITE POLES BY THE SPINDLE FIBERS. D. TELOPHASE- EACH POLE OF THE CELL HAS IDENTICAL COPIES OF THE CHROMOSOMES. A NEW NUCLEAR MEMBRANE FORMS AROUND EACH SET OF CHROMOSOMES. THE SPINDLE FIBERS DISSOLVE. THE CHROMOSOMES UNCOIL.

26. Cytokinesis – The division of the cytoplasm and its contents. In animal cells a cleavage furrow separates the contents, but in plant cells a cell plate separates the contents.

27. -THE END RESULT OF MITOSIS AND CYTOKINESIS IS TWO IDENTICAL DAUGHTER CELLS THAT WILL EACH ENTER THE G1 PHASE OF INTERPHASE.

28. 2. Apoptosis - Programmed cell death. As a part of the cell cycle, some cells are supposed to die at the end of their cycle.

29. 3. CANCER- WHEN A MUTATION(CHANGE IN THE DNA) CAUSES UNCONTROLLED CELL DIVISION.

30. 4. Stem Cells  Unspecialized cells that can develop into specialized cells when under the right conditions

33. *BACTERIA ARE PROKARYOTES(NO MEMBRANE-BOUND ORGANELLES). THEY DIVIDE QUITE SIMPLY BY REPLICATING THEIR DNA AND THEN PINCHING IN TWO. THIS IS CALLED BINARY FISSION. IT RESULTS IN TWO IDENTICAL CELLS.

36. 1. ALL OF THE CELLS IN THE HUMAN BODY ARE DIPLOID(HAVE 2N OR 46 CHROMOSOMES) EXCEPT FOR THE GAMETES (SEX CELLS). FEMALE GAMETES = EGGS, MALE GAMETES = SPERM. EACH OF THESE CELLS ARE HAPLOID (OR 1N = 23). 2. MEIOSIS – THE PROCESS BY WHICH GAMETES ARE FORMED. -MEIOSIS HALVES THE NUMBER OF CHROMOSOMES IN A CELL AND PROVIDES OPPORTUNITIES FOR RESHUFFLING OF THE DNA WHICH IS IMPORTANT FOR PROVIDING VARIETY IN OUR SPECIES.

37. 3. BEFORE MEIOSIS CAN BEGIN, THE DNA IS REPLICATED IN THE CELL. 4. HOMOLOGOUS CHROMOSOMES – PAIR OF CHROMOSOMES THAT ARE SIMILAR, BUT NOT IDENTICAL. ONE CAME FROM THE MOTHER AND ONE FROM THE FATHER. EACH CODES FOR THE SAME BASIC CHARACTERISTIC, BUT THEY MAY CODE FOR VARYING TYPES OF THE CHARACTERISTIC. -EXAMPLE- YOU HAVE TWO #1 CHROMOSOMES –ONE FROM YOR MOTHER AND ONE FROM YOUR FATHER. EACH MAY CODE FOR HAIR COLOR, BUT ONE MAY CODE FOR BLOND AND THE OTHER FOR RED HAIR.

38. 5. THE PHASES OF MEIOSIS- THERE ARE 2 MEIOTIC DIVISIONS: A.PROPHASE 1- THE HOMOLOGOUS CHROMOSOMES, THAT HAVE EACH BEEN REPLICATED, PAIR UP WITH EACH OTHER. This pair of pairs is called a tetrad and their pairing is called synapsis. DIVISION #1: -The nuclear membranes break down. -Spindles form.

39. -CROSSING OVER IS EXTREMELY IMPORTANT BECAUSE IT IS ONE OF THE WAYS THAT OUR SPECIES MIXES DNA FROM ONE GENERATION TO THE NEXT. THIS GIVES US GREAT VARIETY IN OUR SPECIES. *Crossing over also occurs during Prophase I of meiosis. Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes.

41. B. METAPHASE 1- CHROMOSOMES ALIGN AT THE EQUATOR. *Notice that tetrads (4 chromatids) are formed.

42. During meiosis, the pairs of homologous chromosomes are divided in half to form haploid cells, and this separation, or assortment, of homologous chromosomes is random. This means that all of the maternal chromosomes will not be separated into one cell, while the all paternal chromosomes are separated into another. Instead, after meiosis occurs, each haploid cell contains a mixture of genes from the organism's mother and father. Independent Assortment of chromosomes occurs during Metaphase I *Independent Assortment is another important source of genetic variation in meiosis!

44. C. ANAPHASE 1- HOMOLOGOUS PAIRS ARE SPLIT AND MOVE TOWARDS OPPOSITE POLES.

45. D. TELOPHASE 1- CHOMOSOMES REACH OPPOSITE POLES THE CELL DIVIDES IN TWO. PRESENTLY THERE ARE 2 DIPLOID CELLS THAT DO NOT HAVE IDENTICAL DNA.

46. THE SECOND MEIOTIC DIVISION BEGINS: E. PROPHASE 2- CHROMOSOMES COIL AND MOVE TOWARDS THE EQUATOR.

47. F. METAPHASE 2 – CHOMOSOMES ALIGN AT THE EQUATOR.

48. G. ANAPHASE 2 – THE TWO COPIES OF THE CHROMOSOMES ARE SEPARATED AND BEGN TO MOVE TO OPPOSITE POLES.

49. H. TELOPHASE 2 – CHROMOSOMES REACH THE POLES. THE CELL PINCHES IN TWO.

50. -THE RESULT OF MEIOSIS IS 4 NONIDENTICAL, HAPLOID CELLS. IN A FEMALE THIS OCCURS IN THE OVARIES PRODUCING HAPLOID EGGS. IN MALES, THIS OCCURS IN THE TESTES, PRODUCING HAPLOID SPERM.

54. -The cells formed from meiosis are sex cells called gametes. -Gametogenesis (formation of gametes) occurs differently in males and in females. *Males form 4 haploid sperm while females form only one viable egg and three polar bodies.

55. A final source of genetic variation occurs during fertilization. Remember that the sperm of a male are greatly varied and the eggs of a female are greatly varied. When fertilization occurs it is random chance as to which sperm and which egg will unite to form the zygote.