C.   Fertilization & Development In Animals
       only   -- ANSWERS
 
         1.      C L E A V A G E  (it means splitting) is from same root word as this (Fig. 1) butcher's tool
               known as a  C L E A V E R 
                                                                            

      Cleavage is a special event following asexual cell division (M I T O S I S)  in which cells divide to form new daughter cells, but they do NOT then G R O W .  They do not enter INTERPHASE 
After each cell division, each daughter cell must be  S M A L L E R   than in the previous generation.     

      The two daughter cells should each be  only  H A L F  the size of the original  mother cell,
but this diagram set does Not accurately show this size reduction. 

      (A special mitosis blessing for the recently departed mother cell follows!)

      "Dearly beloved former mother cell, may you now rest in pieces"

   The size of each daughter cell after the first cleavage division is only ONE   H A L F  
of the size of the former mother cell.   After the second cleavage division, each daughter
cell is now  ONE   Q U A R T E R   of the size of the former mother cell. 

      Of course, since cleavage is a form of  M I T O S I S, all the daughter cells are genetically
I D E N T I C A L  to each other (and the former  M O T H E R).    You might even say that in the word Mitosis, the second letter which is an  _ I _ signals that the daughter cells are I D E N T I C A L   to each other.

a.       If during early cleavage and before cells start to become different (the process of   
D I F F E R E N T I A T I O N), the dividing embryonic mass separates into two,
_ IDENTICAL_ twins are produced.

                       
These twins IN Fig. 4 resulted from an original _ 1 _ egg(s) + _ 1 _ sperm

b.      The other more common kind of twins (F R A T E R N A L) resulted from
_ 2 _ egg(s) + _ 2 _ sperm

      

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