- -  AGRICULTURE CORE CURRICULUM  - -

(CLF3000)  Advanced Core Cluster:  ANIMAL SCIENCE

  (CLF3250)  Unit Title:  LIVESTOCK BREEDING AND GENETICS

____________________________________________________________________________
  (CLF3251)  Topic:  SPERM AND EGG             Time             Year(s) 
                     PRODUCTION               2 hours            3 / 4        
____________________________________________________________________________

          Topic Objectives:  Upon completion of this lesson, the student 
                             will be able to:

          Learning Outcome #:

            (D-2)  -  Draw and describe the difference between oogenesis
                      and spermatogenesis.

            (D-8)  -  Describe the genetic factors that influence the sex of
                      an offspring.

          Special Materials and Equipment:  Microscopes, prepared slides of
                      actual sperm and eggs, Supplemental Worksheet #1.

          References: Hafez, E.S. (1974). REPRODUCTION IN FARM ANIMALS (3rd 
                        ed.).                     
                      Ronning, Magnar and Cole, H.H. (1974). ANIMAL 
                        AGRICULTURE.                    

          Evaluation: Quiz by instructor, completion of Supplemental 
                      Worksheet #1.


TOPIC PRESENTATION:  SPERM AND EGG PRODUCTION

REVIEW:  Basic Core Curriculum, Animal Science CLF251 (includes simple 
         diagrams and a glossary of terms)

A.  Oogenesis is the process of the formation of eggs with GONOCYTES and 
    OOCYTES.  

    1.  Gonocytes:

        a.  Are the precursors of both male and female gametes (sex cells).

        b.  Originate in the embryonic animal during its formation in the
            womb.


    2.  Oocytes:

        a.  Are gonocytes that have differentiated in the fetal ovaries.

        b.  They are the sole reservoir of all future ova.

    3.  Growth of the oocyte:

        a.  Stage 1 - the OOCYTE grows in size (lasts from birth to 
            puberty),

        b.  Stage 2 - the OOCYTE and follicle matures (during puberty).

    4.  Cell division occurs during Stage 2 of oogenesis (above):

        a.  The OOCYTE undergoes 2 meiotic divisions during which 2 daughter
            cells arise, each having half the chromosome complement.

            1)  One of these 2 daughter cells acquires nearly all of the
                cytoplasm, and this large cell is called the SECONDARY 
                OOCYTE.

            2)  The much smaller cell with only a little cytoplasm is called 
                the POLAR BODY.

        b.  At the second maturation division, the SECONDARY OOCYTE 
            divides into the OOTID and a second POLAR BODY.

        c.  The POLAR BODIES degenerate, leaving the OOTID ready for
            fertilization.

    5.  Onset of oogenesis:

        a.  The OOTIDS or OVUM actually undergo oogenesis at different
            times, depending on the species.

        b.  Most mammals ovulate just as Meiosis I has been completed.

B.  Spermatogenesis is the process of sperm formation which commences at 
    puberty.  The process is discussed below:

    1.  Spermatogonia:

        a.  At birth, SPERMATOGONIA and indifferent cells are present in the
            seminiferous tubules.

        b.  These SPERMATOGONIA also are called SPERM MOTHER CELLS.


    2.  Phases of spermatogenesis:

        a.  SPERMATOGONIA undergo mitotic division and become dormant, thus 
            ensuring a continuous supply of SPERMATOGONIA.

        b.  One SPERMATOGONIUM becomes active and divides 4 more times so 
            that there are now 16 PRIMARY SPERMATOCYTES.

        c.  These primary spermatocytes go through meiotic division. 

            1)  At this time, the number of chromosomes is HALVED.  

            2)  These new cells are now called SECONDARY SPERMATOCYTES.
 
        d.  The secondary spermatocytes undergo one more division to become
            SPERMATIDS.

        e.  SPERMATIDS undergo a metamorphosis which involves a radical 
            alteration in cellular form during which most of the cytoplasm
            is lost. 

          __________________________________________________________
          ACTIVITY:
  
          1.  Observe sperm or ova under a microscope.

          2.  Complete Supplementary Worksheet #1.            
          __________________________________________________________

 
C.  Sex Determination
 
    1.  Every cell in the mammalian body, except the gametes (sperm and 
        ova), contains a pair of sex chromosomes.
 
        a.  In females, the 2 members of the sex chromosome pair resemble
            one another and are known as the X chromosomes (XX).

        b.  In males, the sex chromosomes differ from one another, one is 
            the  X chromosome, the other is smaller and is called the Y 
            chromosome (XY).
 
    2.  The gametes contain only a single sex chromosome.

        a.  In the female, each ovum contains an X chromosome. 

        b.  In the male, the sperm contains either an X or a Y chromosome.

    3.  In normal fertilization, the embryo develops as a male or female 
        according to whether the ovum is fertilized by a sperm carrying an
        X or a Y chromosome.  In effect, the father determines the sex of 
        the offspring.

 
D.  Influencing the Sex of the Offspring
 
    1.  If the 2 types of sperm are present in equal numbers, the ratio of
        male to female sperm at the time of conception should be 1:1.
 
    2.  Treating the semen to alter this ratio has been attempted, but so
        far this has been unsuccessful.

         a.  The sex of the offspring is important to many livestock 
             producers since one sex may be more valuable than the other,
             depending on the circumstances.  For example:
 
             1)  beef cattle - steers bring a higher market price than
                 heifers;

             2)  dairy cattle - heifers are the milk producers so they are
                 more valuable than bull calves; and

             3)  poultry - egg production operations keep all the laying hen 
                 chicks, but often dispose of the male chicks.
 


 


Supplemental Worksheet #1                   SPERM AND EGG PRODUCTION


Name___________________________________

Date___________________________________

Per.___________________________________


1.  Define oogenesis:
 



2.  Define spermatogenesis:

 


3.  Give a description of the following cells:

    a.  gonocytes - 



    b.  oocytes - 



    c.  polar bodies - 



    d.  spermatogonia - 



    e.  spermatid - 




4.  Diagram the process of oogenesis starting with oocytes in Stage 1 of 
    oogenesis.  (Use an additional sheet of paper).


5.  Diagram the process of spermatogenesis starting with spermatogonia in
    Phase A.  (Use another sheet of paper!!).


4/16/90 sg/gv


#%&C