The Cell Cycle, Mitosis Meiosis

							   The Cell Cycle, Mitosis &
            Meiosis

                        198-
       Chapter 5 (pages 198-199)
                    (250-
         Chapter 7 (250-251)




        Questions to Ponder
Why do cells undergo Mitosis?
If cells replicate themselves, how do they
make exact copies of themselves?
How do cells split and still maintain the correct
number of chromosomes?
How do cells split and not get smaller and
smaller in size?




   Interphase and the Control of
           Cell Division
During most of the cell
cycle the cell is in
interphase,
interphase, which is
divided into three
subphases:
subphases: S, G1, and
G2. DNA is replicated
during S phase.
Interphase is not a part
of Mitosis. Figure 9.4




                                                    1
   Mitosis: Distributing Exact Copies of
            Genetic Information
Mitosis is splitting the
genetic material, not the
cell.
After DNA is replicated
during S phase, the first
sign of mitosis is the
separation of
centrosomes,
centrosomes, which
initiate microtubule
formation for the spindle.
Review Figure 9.9




                                        figure 09-08a.jpg




                    Figure 9.8
                     – Part 1

                 Figure 9.8 – Part 1




                                        figure 09-08b.jpg




                     Figure 9.8
                      – Part 2
                  Figure 9.8 – Part 2




                                                            2
Mitosis: Distributing Exact Copies of
         Genetic Information
Prophase: chromosomes condense
and appear as paired sister
chromatids.
chromatids. Chromosomes move
toward the middle of the spindle

Metaphase: they gather at the middle
of the cell, their centromeres on the
equatorial plate




Mitosis: Distributing Exact Copies of
         Genetic Information
End of Metaphase: Centromeres separate.
Anaphase: daughter chromosomes migrate
to its pole along the microtubule track.
Telophase:
Telophase: chromosomes unwind, nuclear
                         re-
envelopes and nucleoli re-form.
Product: two nuclei with identical
chromosomes are formed.




Cytokinesis: The Division of
      the Cytoplasm
Cytokinosis:
Cytokinosis: Cell Division. Animal
cells-
cells-cytoplasm usually divides by
plasma membrane furrowing caused
by contraction of cytoplasmic
                       cells-
microfilaments. Plant cells- cytokinesis
by vesicle fusion and the synthesis of
new cell wall material.
Diploid Cell gives rise to two Diploid
Cells




                                           3
                Watson & Crick 1953




       Function of Mitosis
Cell replacement
Tissue repair
Asexual reproduction

Results in cloned cells genetically identical
to parent cells




                                                4
Meiosis: A Pair of Nuclear
        Divisions
Meiosis: Reduces the chromosome
number from diploid to haploid and
ensures that each haploid cell contains
one member of each chromosome
pair.
                           divisions—
It consists of two nuclear divisions—
Meiosis I and Meiosis II




                                                      figure 09-14a.jpg




           Synapsis:        Crossing over: exchange of genetic material




         Figure 9.14 of chromosome arms
                  Interlinking


           – Part 1

         Figure 9.14 – Part
                  1




                                                       figure 09-16.jpg




            Figure        Hugging

             9.16
                       Crossing over leads to




             Figure 9.16




                                                                          5
                                                              figure 09-14b.jpg




                     Figure 9.14
                       – Part 2

                  Figure 9.14 – Part 2




  Meiosis: A Pair of Nuclear Divisions
 Many events are the same as mitosis, here are some differences
Prophase I: A) homologous chromosomes pair, B)
material may be exchanged by crossing over between
nonsister chromatids of two homologous
chromosomes.
Metaphase I: the paired homologs gather at the
equatorial plate.
Anaphase I: entire chromosomes, each with two
chromatids,
chromatids, migrate to the poles.
Telophase I: two nuclei, each with the haploid number
                                chromatids.
of chromosomes with two sister chromatids. Review
Figures 9.14, 9.16
        9.14,




     Meiosis: A Pair of Nuclear
             Divisions
    Intephase II: No DNA Replication
    Meiosis II: sister chromatids separate.

    The result of meiosis is four cells, each with
    a haploid chromosome content, and genetic
    uniqueness. Eggs and Sperm




                                                                                  6
                                       figure 09-17a.jpg




       Figure 9.17 –
          Part 1

         Figure 9.17 – Part 1




                                       figure 09-17b.jpg




               Figure
               9.17 –
               Part 2

         Figure 9.17 – Part 2




Meiosis: A Pair of Nuclear
        Divisions
Both crossing over during prophase I and
the random selection of which homolog of a
pair migrates to which pole during anaphase
I ensure that the genetic composition of
each haploid gamete is different from that of
the parent and from that of the other
gametes. The more chromosome pairs
there are in a diploid cell, the greater the
diversity of chromosome combinations
generated by meiosis.




                                                           7