Principles of Heredity

Williamson, Morris         Esmond School
                           238-6243
                      

Objectives:

To learn the role of genes in inheritance                                  
To understand the idea of dominant and recessive genes
To understand the role of chance in the inheritance of traits
                                                                         
Apparatus needed:

craft sticks or tongue depressors, construction paper
colored markers, self-adhesive labels, 5/16" x 1/2"
2 transparencies, overhead projector

Recommended strategy:

The labels are applied to the craft sticks, which will represent 
chromosomes, in different positions for each trait.  The labels 
represent genes. Seven traits are being considered:  stem length, 
flower position, seed shape, seed color, seed coat color, pod shape 
and pod color.  Different colored labels are used to represent the 
various traits.  There should be a pair of sticks for each dominant 
and each recessive trait.  A capital letter is used for the dominant 
trait, and a lower case letter for the recessive trait. 

Make a key for the traits for a garden pea plant, and give one to each 
student.  Make a transparency diagramming meiosis using letters in 
lieu of sex cells.  Make another transparency of a Punnet Square, 
diagramming the cross of the F1 gametes from the first transparency. 
Have a vocabulary sheet with the following information and 
definitions:  Gregor Mendel, dominant character, recessive character, 
alleles, homozyous, heterozyous, hybrid, genotype, phenotype, Law of 
Dominance, Punnet Square, F1, F2, trait, gene and heredity. 

Begin the lesson by showing pictures of animals from the same litter 
and ask about their similarities and differences.  Ask if they have 
noticed any similarities and differences among family members.  Lead 
into the concepts of inheritance and heredity. 
 
Lead into the fact that the study of heredity is called genetics.  
Pass out chromosome sticks and the nucleus cut from construction 
paper.  Review meiosis and ask what the sticks and labels are 
representative of based on our study of meiosis.  Use the chromosome 
models to lead into the concepts of: chromosome pairs, genes, dominant 
trait, recessive trait, heterozyous, genotype and phenotype.  Discuss 
the meanings of the various word roots and go over the definitions on 
the vocabulary sheet.  When discussing each concept, use the board to 
illustrate each.  The students should also be moving and grouping 
their chromosome/gene models in the "nucleus" to correspond with each 
concept.  Ask the class to give the genotype and phenotype of their 
various combinations. 

Introduce to the Punnett Square by randomly shuffling two homologous 
sets of chromosome sticks and asking them what combinations they think 
might occur when you separate into pairs.  Discuss chance and ask what 
games of chance with which they are familiar.  Tell them that the 
Punnett Square is a method of determining the probability of certain 
combinations. 

Use the transparency with letters for gametes and discuss what would 
be the result of a cross between F1 offspring.  Then introduce the 
transparency with the Punnett Square and diagram results. 

Now, on their own have create various gene combinations with their 
chromosome models.  Have them describe the genotype and phenotype.  
Give examples of various F1 crosses to use with a Punnett Square.  
Also, have them list traits that they have in common with their 
parents, grandparents or other relatives.