GENETICS & DEVELOPMENT - Cell Division
   
    Physical Basis of Inheritability...                          Key Concepts*
           Mechanisms of Cell Reproduction...    egg  &  sperm cells
                 cells reproduce identically, yet w variation (new traits)
                       "All living cells arise from pre-existing cells"

    GENETICS asks....   HOW?   mechanisms at cellular  &  molecular level

    DEVELOPMENT looks....   at the LIFE CYCLE of organisms
            1.   reproduction mechanisms of organisms
            2.  growth of organism..... zygote to adult
                           cell differentiation - how one cell becomes different from another
                           differential gene activity - genes are active at different times
                           totipotency & cloning - exact genetic copies 
  

 

 

 

 

  

METHODS of CELL REPRODUCTION include...

     Fission*  - binary = 2 equal halves (bacteria  &  cyanobacteria  &  protozoans)

      Budding* - outgrowths detach = new organism (unequal)
                                                                            (hydra)                 Chapter 46.1 video: Video: Hydra Budding
     Mitosis* - asexually = identical genetic copies [cytokinesis*]
                              genetically equal somatic cells 
c7 fig 1.5 lung cell*
                                                                                     amoeba, bone, marrow, & fertilized egg cell divisions
     Meiosis* - sexually produces sperm & egg cells with    
                               1/2 chromosome # & new gene combos

 

 

 

 

 

 Mitosis -  Asexual Reproduction Cell Cycle...  
                      results in copying & equal duplication of parental cell's  DNA  
                      and the equal division of chromosomes into two daughter cells
                           (rates =   liver cells  1x/yr    -    epithelial cells  1x/day)

 
the Life cycle of a Cell... is referred to as the "CELL CYCLE"...    
                                                                                                           Concept Activity 12.2 - The Cell Cycle
 
[3 Stages] - Cell Cycle is depicted as a circle 360o  fig 12.5*     [G1 - S - G2 - M]                
        Interphase - period between successive divisions of a cell
                            3 parts =    G1 - before,   DNA synthesis (S),    &   G2 period after
       
MITOSIS - nuclear division phase;    separation & duplication of chromosomes
        Cytokenesis* - physical division of cell into two parts: animals/plants

  How does one determine the times of the phases of Cell Cycle ? 
         fibroblast cell cultures*          S-phase: pulse chase-experiments*  
                                                               Investigation 12.2 -   How much time is spent in each phase of cell cycle


                

                          
                          

 

 

 

   

 Stages of Mitosis- pics*     Sumanas, Inc. animation - Mitosis*
 
Prophase -                             Concept activity 12.2  Mitosis and Cytokinesis Video
    chromatin condenses into chromosomes    

prophase.jpg (23703 bytes)

 Prometaphase -
    chromosome MT's attach to kinetochores
    fig 12.6*
    each homolog has 2 chromatids   

prometaphase.jpg (22842 bytes)

 Metaphase                Concept Activity 12.2  Mitosis & Cytokinesis Animation
    chromosomes align at equator                  
     fig 12.6*
    homologs align independently of each other

metaphase.jpg (20290 bytes)

 Anaphase -
    MT attached to kinetochore;   chromatids  
  fig12.8*
    are pulled apart & poles move apart        

anaphase.jpg (25058 bytes)

 Telophase -                                 onion root tip cells*
    chromosomes at opposite poles;        
    daughter cells form by cytokinesis                next 

telophase.jpg (19976 bytes)

                  
               
              

 

   
Names and Numbers -  (to protect the innocent)                                         

Chromosomes*
  Genes occur in chromatin of nucleus, 
        which condense into  CHROMOSOMES
        (colored bodies) visible only during MITOSIS
 
  
                                          
animation of DNA coiling into chromosomes

        bacteria have about 3,000 genes                 &       1  chromosome
        humans have some   20 to 25,000+ genes    &     46  chromosomes

        Humans have 46 chromosomes  or  23 HOMOLOGOUS pairs
                   
                 23 maternal chromosomes
                                     
23 paternal chromosomes
 

 

 

 

 

 
 Control of Cell Division and the Cell Cycle      2001 Nobel prize
     Regulated by "Growth Factors" - proteins that promote cell division
         MPF - mitotic promoting factor...   [ complex* of two proteins  cdk + cyclin]
                      MPF is a kinase enzyme, ones that switches on/off target cell cycle
                       proteins by phosphorylating them.....
                                       inactive cycle protein  ---------------->    active-P

                                                                 ATP ---> ADP
         MPF promotes entrance into mitosis from the G2 phase by phosphorylating multiple
         proteins during mitosis including one that leads to destruction of cyclin itself 
           MPF
cdk - a cell division control protein - cyclin dependent kinase;
                                             active only when bound to cyclin
                  
  cyclin -  a protein whose amount varies cyclically*;
                                             when in high concentrations
*, binds to cdk makes MPF...  
                                                               [cyclin + cdk = MPF]...    favors Mitosis

   
 Growth Factors regulate at critical points...   Cell cycle checkpoints* 
                                                                                               Concept Activity - 12.1 - Roles of Cell Division

  


   

 

 

  
 
SEXUAL CELL REPRODUCTION...    "MEIOSIS" 
      
                                                                                                              
  compare physical differences
* between nuclear division of  MEIOSIS  &  MITOSIS  
     

   so the Distinct Differences are:
                                                             Key Concepts*
            meiosis  =  4 progeny cells  [1 = 2 = 4]... 
thus 2 divisions
            mitosis  =  2 daughter cells only... 
thus 1 cell division

            meiosis  =  one-half number of chromosomes
            mitosis  =  same # of chromosomes as parent cell

            meiosis  =  new combinations of gene not in parents & 
                              chromosomes sort randomly of each other
        mitosis  =  daughter cells are genetically identical

 

 

     

 
Sexual Cell Reproduction   (Meiosis)
      Where does meiosis occur during sexual cell cycle ?
                Meiosis  --->  produces  cells
half chrm # = 23    (sperm & egg - haploid)
                fertilization   (sperm + egg)  ----->    
diploid life cycle*      (chrm # = 46)
                                         
  Alternation of Generations*   &    Human life Cycle     
                                                                                                    Concept Activity 13.1 - 
Asexual and Sexual Life Cycles 

 
Stages of Sexual Cell Division

                same 3 phases...   
just as in asexual division   
                      
(Interphase,  Nuclear Division,  Cytokinesis)

                                 but,  2 Divisions    Meiosis I       and    Meiosis II
                                                          1 cell   =   2 cell    =         4 cells

          

 

 

 


Names of stages are same & have analogous functions
   
Meiosis I...                                      
                Prophase I     =  chromosomes condense
                                           SYNAPSIS - homologs PAIR together = tetrad
                                           CROSSOVER
* - exchange at chiasma* 
                Metaphase I  =  chromosomes align at equator                                 
                Anaphase I    =  chromosomes migrate toward poles
                Telophase I   =  chromosome at poles - cell domains separate
                        Meiosis I   separates homologs of homologous pair*
  fig 13.7*
   

   Meiosis II...   is just like mitosis             
                 separates chromatids of one homolog of the homologous pair
                                                     just as is done in mitosis
                Comparison
(fig 13.9)* of Mitosis/Meiosis  -  comparison animation
                Independent Assortment
* - random alignment homologs (fig)
          Crossing Over - exchange of chromosome material

                                         Concept Activity 13.3 -
Meiosis Animation     
Sumanas, Inc. animation of Meiosis*                   

 

 

 

 

     Summary of MEIOSIS      [table of differences]*
1.   Nuclear division phase of sexual cell reproduction
2.  Two successive divisions, results in 4 daughter cells...
               Meiosis 1 and Meiosis 2
3.  Reduction/division occurs....   diploid  ---->  haploid
               daughter cells ½ number of parent cell chromosomes
4.  Stages have same nomenclature as Mitosis
               prophase, metaphase, anaphase, telophase, M1 & M2
5.  Only one S phase, where DNA is duplicated
               often may be no interphase between M1 & M2
6.  Homologs separate in Meiosis 1
               Chromatids separate in Meiosis 2 (mitotic-like)
7.  Random Assortment occurs......  homologs align 
               at equitorial plates independent of each other
8.  Crossing over... may occur in Prophase I...
               synapsis = close pairing homologs allows exchange
        chiasma = point exchange of sister chromatids     

 

 

 

 

 

 

 

   Consequences of sex... 

        
new gene/chromosome combos
         that did not exist in either parent,
         which will become the stuff of evolution
...

                                                             

            next lecture                                            a paradigmKey Concepts*

 

 

 

 

 

 

 

 

 Duplication of DNA during Meiosis and Mitosis*