Bio1151 Chapter 12 The Cell Cycle
  1. The continuity of life is based upon cell           , the reproduction of cells.

      The average eukaryotic cell is about 100 µm (100 x 10^-6 m. = 10^-4 m.) long. You have 200 trillion (2 x 10^14) somatic cells (p. 220). Total length of your cells lined up end-to-end: (2 x 10^14) x (10^-4 m.) = 2 x 10^10 m. = 2 x 10^7 km. The earth's circumference is 40 million m. (40 x 10^6 m. = 4 x 10^7 m. = 4 x 10^4 km. 2 x 10^7 km. / 4 x 10^4 km. = 500: your cells can wrap around the earth 500 times. Updated Dec 18, 2008 by Peter Chen


      Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism. Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells. Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells.
     
     
     
     
  2. Prokaryotes reproduce by a type of cell division called         fission, where the DNA is             , and the cell splits, producing      "daughter" cells.

      Bacterial cell division (binary fission) Chromosome replication begins at the origin of replication where replication begins. One copy of the origin moves toward the other end of the cell; DNA is deuplicated. When one copy of the origin reaches the other end of the cell, replication is complete. The plasma membrane grows inward, and new cell wall is deposited. Two daughter cells result.
     
     
     
     
  3. Eukaryotic DNA is packaged into            that condenses into              during cell division.

      DNA in nondividing eukaryotic cells (far left and far right) is complexed with proteins in dispersed fibers called chromatin. The chromatin condenses into visible chromosomes during cell division in a process called mitosis.


      Eukaryotic chromosomes condense and become visible during cell diviison.


      To prepare for cell division, DNA is replicated and each duplicated chromosome has 2 sister chromatids, attached by a centromere. The chromatids separate during cell division.
     
     
     
     
  4.          (nonreproductive) cells have    sets of chromosomes (diploid) and reproduce asexually by          , while          (sex cells) have    set of chromosomes (haploid) and reproduce by          .

      An idealized life cycle of animals. Haploid gametes fuse by fertilization to form a diploid zygote. The zygote undergoes many rounds of mitosis to produce the diploid multicellular organism. Diploid germ cells undergo meiosis ro produce haploid gametes.
     
     
     
     
  5. Mitosis is preceded by an             ; together these constitute the cell        .

      The cell cycle. The mitotic (M) phase alternates with interphase, which is composed of 2 growth phases (G[1] and G[2]) and a S (DNA synthesis) phase. In the M phase, mitosis divides the nucleus, and cytokinesis divides the cytoplasm, producing 2 daughter cells.
     
     
     
     
  6. The mitotic phase consists of          , the division of the nucleus, and              , the division of the cytoplasm.
     
     
     
     
    • Mitosis consists of 5 phases, or stages: 1)           , 2)               , 3)            , 4)           , 5)            .

        Stages of mitosis. From the G2 subphase of Interphase, the dividing cell proceeds through prophase to prometaphase. continue


        Stages of mitosis continued. A dividing cell continues through metaphase, anaphase, and finally telophase and cytokinesis.
       
       
       
       
    • Prophase

        Prophase. The chromatin fibers condense into discrete chromosomes observable with a light microscope. The nucleoli disappear. The mitotic spindle, composed of microtubules, begins to form.
       
       
       
       
    • Prometaphase

        Prometaphase. The nuclear envelope fragments. Each of the 2 chromatids has a kinetochore, which attach the chromatid to the spindle microtubules at the centromere.
       
       
       
       
    • Metaphase

        Metaphase. The chromosomes convene on the metaphase (equatorial) plate. For each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles.
       
       
       
       
    • Anaphase

        Anaphase. The 2 sister chromatids part, moving toward opposite ends of the cell, Each chromatid is now a full-fledged chromosome. The kinetochore microtubules shorten, while nonkinetochore microtubules lengthen, stretching the cell.
       
       
       
       
    • Telophase

        Telophase. Two daughter nuclei begin to form in the cell. Nuclear envelopes reform. The chromosomes become less condensed. Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete.
       
       
       
       
    • Cytokinesis:
       
       
       
       
      • Animal cells

          Cytokinesis in animal cells. In animal cells, a cleavage furrow forms, pinching the plasma membrane. Then a contractile ring of microfilaments splits the cell.
         
         
         
         
      • Plant cells


      Cytokinesis in plant cells. In plant cells, vesicles containing cell wall material fuse to form a cell plate. The cell plate grows and fuses with the existing cell wall, dividing the cell in two.
     
     
     
     
    Review: Mitosis and Cytokinesis
Bio1151 Chapter 13 Meiosis and Sexual Life Cycles
     
     
     
     
  1. In          reproduction, one parent produces genetically            ffspring by         fission or by          .

      Bacterial cell division (binary fission) Chromosome replication begins at the origin of replication where replication begins. One copy of the origin moves toward the other end of the cell; DNA is deuplicated. When one copy of the origin reaches the other end of the cell, replication is complete. The plasma membrane grows inward, and new cell wall is deposited. Two daughter cells result.


      The asexual reproduction of a hydra. The bud, a localized mass of mitotically dividing cells, develops into a small hydra, which detaches from the parent.
     
     
     
     
  2. In         reproduction, two parents produce offspring that have unique combinations of        inherited from each parent.
     
     
     
     
  3. A            is an ordered, visual representation of the              in a cell.

      A karyotype is a display of condensed chromosomes arranged in pairs. A digital photograph of chromosomes of a cell in mitosis is electronically arranged into pairs according to size and shape. This karyotype shows the chromosomes from a human male. Each chromosome consists of 2 sister chromatids.
     
     
     
     
  4. In humans, each          cell has     chromosomes made up of two sets, with one set coming from each parent.
     
     
     
     
    • 44 of these are pairs of             chromosomes, or            , and have the same        ; each of the pair comes from each of the parents of the individual.
       
       
       
       
    • The other two chromosomes are      chromosomes, called X and Y, which determine the gender of the individual. Cells having a full complement of chromosomes are          .

        Human somatic cells have 22 pairs of homologous autosomes plus one pair of sex chromosomes. XX individuals are female, while XY are male.
       
       
       
       
    • Each chromosome consists of two identical sister             , attached to the             .


      A chromosome consists of 2 sister chromatids joined at the centromere. Each homologous pair is composed of one chromosome from the maternal set and one from the paternal set.
     
     
     
     
  5.          are          sex cells that are produced from       cells in organs called         by meiosis.

      The human life cycle. Ovaries produce the female gamete ovum, and testes produce the male gamete sperm. The gametes are haploid, consisting of one set (n = 23 in humans) of chromosomes. The number of chromosomes in the diploid zygote and all somatic cells arising from it is 46, consisting of two sets (2 n = 46).
     
     
     
     
  6.                occurs when a sperm fuses with an ovum, forming a diploid         , which grows and develops into an adult organism.

      An idealized life cycle of animals. Haploid gametes fuse by fertilization to form a diploid zygote. The zygote undergoes many rounds of mitosis to produce the diploid multicellular organism. Diploid germ cells undergo meiosis ro produce haploid gametes.
     
     
     
     
  7. Since meiosis reduces the number of chromosome sets from          to          , two cellular divisions are required, preceded by a single             .

      Overview of meiosis. After chromosomes replicate in interphase, the diploid cell divides twice, yielding four haploid daughter cells. One chromosome was inherited from the female parent, the other from the male parent.
     
     
     
     
  8. Meiosis    is the chromosome            division, and meiosis     produces       haploid daughter cells.

      Meiosis I separates homologous chromosomes and results in reduction from diploid to haploid cells. continue


      Meiosis II separates sister chromatids, producing 4 haploid cells.
     
     
     
     
    • Prophase I

        In prophase I, homologous chromosomes pair up into tetrads in a process called synapsis. Crossing over of DNA segments occurs at chiasmata, and genetic information is exchanged between the homologues.
       
       
       
       
    • Metaphase I

        In metaphase I, the paired tetrads, formed by synapsis during prophase I, line up on the metaphase plate. Note the alignment of maternal and paternal homologues along the metaphase plate is random.
       
       
       
       
    • Anaphase I

        In anaphase I, the homologous pairs move toward opposite poles of the cell. Notice sister chromatids remain attached, and some of the chromatids have exchanged genetic material.
       
       
       
       
    • Telephase I and Cytokinesis I

        At the end of telephase I and cytokinesis I, two haploid cells are produced with two chromatids still attached to each chromosome.
       
       
       
       
    • Meiosis II


      Meiosis II is similar to mitosis, except the cell undergoing division is haploid rather than diploid, and sister chromatids separate in anaphase II. Meiosis now has produced 4 haploid cells.
     
     
     
     
    Summary.

      Mitosis
    • One cell division produces two diploid, genetically identical daughter cells.
    • Functions in growth and repair of somatic cells. Meiosis
    • Two cell divisions produce four haploid, genetically different daughter cells.
    • Synapsis of homologous chromosomes, forming tetrads and resulting in crossing over between sister chromatids.
    • Produces gametes for sexual reproduction and genetic variation of offspring.
     
     
     
     
  9. Sexual reproduction produces genetic            by several mechanisms: independent             , crossing       , and random fertilization.

      In independent assortment, each pair of chromosomes sorts its maternal and paternal homologues into daughter cells independently of the other pairs in metaphase I, giving 2^23, or about 8 million, combinations in humans.


      In crossing over, nonsister chromatids of homologous chromosomes exchange portions. The recombinant chromosomes carry genes derived from different parents.


      The random fusion of gametes during fertilization produces a zygote with 2^23 x 2^23, or over 70 trillion, combinations of chromosomes.
     
     
     
     
  10. The tremendous genetic variation made possible by meiosis and         reproduction provides raw material for evolution by          selection.