Principles of Heredity

Williamson, Morris Esmond School

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.
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