- -  AGRICULTURE CORE CURRICULUM  - -

(CLF3000)  Advanced Core Cluster:  ANIMAL SCIENCE

  (CLF3250)  Unit Title:  LIVESTOCK BREEDING AND GENETICS

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  (CLF3252)  Topic:  REVIEW BASIC             Time             Year(s) 
                     GENETICS                 1 hour             3 / 4        
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          Topic Objectives:  Upon completion of this lesson, the student
                             will be able to:

          Learning Outcome #:

            (D-1)  -  Briefly define the chromosome theory of inheritance.

            (D-3)  -  Review (from the Basic Core) and define the terms:
                      phenotype, genotype, gene, locus, allele, homozygous,
                      heterozygous, variation, and mutation.

          Special Materials and Equipment: Microscopes and slides of
                      chromosomes, VEP video on "Basic Genetics".

          References: California Vocational Agriculture Curriculum
                        Guidelines:  ANIMAL PRODUCTION, "Livestock Breeding 
                        and Genetics".

          Evaluation: Quiz by instructor.


TOPIC PRESENTATION:  REVIEW OF BASIC GENETICS

REVIEW:  Basic Core Curriculum CLF252 and CLF253.

A.  Chromosome Theory of Inheritance

    1.  All plants and animals are made of tiny building blocks called
        cells.

        a.  Each cell is divided from other cells by a cell wall.

        b.  Each cell contains a nucleus in which genetic material called
            "chromosomes" are located.

    2.  Two types of cell division:

        a.  Mitosis - This type of cell division allows for an increase in
            cell numbers (more fat cells or muscle cells for example).
            Cells dividing by the process of mitosis have the same 
            number of chromosomes after division as the parent cell had 
            before division.

        b.  Meiosis - This occurs only in the ovaries and testes to produce 
            the sex cells (ova and sperm).  Cells undergoing meiosis have 
            half the number (haploid) of chromosomes as the parent cell had 
            before division.

    3.  At conception, an individual receives one of each chromosome pair 
        from its father and one of each chromosome pair from its mother.

B.  Review Terms

    1.  Phenotype - The outward appearance or production of the animal.

            example:  black coat color in Angus cattle.

    2.  Genotype - The type of genes the animal carries within him.

            example:  the genotype for black coat color may be Bb 
                      (heterozygous)  or BB (homozygous).

    3.  Gene - The inherited material (DNA) that codes for a trait and
               determines the heritable characteristics of an animal.

            example:  the gene that codes for coat color.

    4.  Locus - The spot on the chromosome occupied by genes affecting 
                a particular trait.

            example:  the coat color locus on the chromosome.

    5.  Allele - One form of a gene.

            example:  In the coat color example above (genotype), "B" and
                      "b" are different alleles.

    6.  Homozygous - When the two alleles at a locus, one from the sire and 
                     one from the dam, are the same.  Animals are pure for a
                     certain characteristic.

            example:  "BB" or "bb" at the coat color locus.

    7.  Heterozygous - When the two alleles at a locus are different, having
                       one dominant and one recessive factor.

            example:  "Bb" coat color.

    8.  Variation - Differences between individuals, either due to genetic 
                    or environmental factors.

    9.  Mutation - Changes in the molecular structure of a gene or genes.

            This is the underlying mechanism for evolution and natural
            selection.


          __________________________________________________________
          ACTIVITY:
  
          1.  Use microscopes to examine prepared slides of 
              chromosomes to reinforce the review and stimulate
              interest.

          2.  If you use slides in a projector, a general discussion 
              may be adequate.  If you use prepared slides, the
              students should make some simple diagrams to accompany
              the exercise.
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