animal life cycle  

Read the pages indicated by G-9 and study behavioral objectives 19, 20 and 21.  Study the figure above which represents the human  life cycle.  In human somatic cells there are 23 pair of homologous chromosomes (total of 46 chromosomes).  If two somatic cells combined during  fertilization the cell formed would  have 92 chromosomes and  with every new generation their would be a doubling  of chromosomes compared to the parent. This does not occur.  You have the same number of chromosomes as your parents and your children.  In order for two cells to combine and contain the same number of chromosomes as the parents the two cells must reduce their chromosome number by one half. 

             note: meiosis 
In humans you would start out with  46  somatic cell chromosomes in both parents.  The sex cells (egg and sperm) will form with only  23 chromosomes per cell.  During fertilization these two cells will combine to form a zygote with 46 chromosomes.   The process where cells with only  one half  the number of chromosomes are formed is called meiosis.  This reduction process is  not random.  You learned earlier that diploid cells contain homologous pair of chromosomes.  During meiosis each new cell formed will receive only one of each homologous pair of chromosomes. During fertilization  one chromosome of each homologous pair  from each parent will combine by fertilization to form  a  diploid (pairs of homologous chromosomes)  zygote which divides by mitosis to develop into an embryo and eventually  an adult. Draw this cycle in your notes and identify the various parts. 

                                 results of meiosis 

The figure above shows the results of meiosis in humans. The somatic mother cell contains 46 chromosomes (top). The newly formed cells contain 23 chromosomes. These cells are haploid because they contain one of each homologous pair of chromosomes. 
 

7. Draw two cells - one containing 3 homologous pair of chromosomes (diploid) and the second showing the chromosome compliment after meiosis forming  a cell with one of each homologous pair (haploid). 
 
Press here to check answer.  press 
 
 
 
 
 
 
 
 
 
 
 
 
 

See question below figure. 
     A                        

      
                 B                      C
                                                                                                             
8.  Which cell(s) represent(s)  a haploid compliment of chromosomes? 

         a) A                       b) B                               c) C 
 
Press here to check answer.  press 
 
 
 
 
 

9.  Where does meiosis occur in humans? 

     a)  all somatic cells   b) selected cells in the testis or ovaries 
 
 
Press here to check answer.  press 
 
 
 
 
 
 
 
 
 
 
 
 

 Examine the figure depicting the  human life cycle and  answer the questions below. 
 
                           cycle 

10.   The sperm cell is:  diploid or haploid. 

Press here to check answer.  press 
 
 
 
 

11.   The zygote is : diploid or haploid 

Press here to check answer.  press 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

12    Another name for the sperm and egg cells: 
 
                        a) gametes     b) somatic body cell 

Press here to check answer.  press 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
This is the end of lesson four. In lesson five, Eukaryotic Cell Cycle - Meiosis, you will learn  the different steps involved during meiosis.  Cell division which reduces the chromosomes  by one half. 

Click here.  click 

For information on how to use this page, go to How to Use This Site.