Lesson Plan:

Lesson Title: From Jeans To Genes

Class Time Required: 45 minutes

Overview and Purpose:
Students are introduced to the structure of chromosomes and genes as these concepts are illustrated utilizing articles of clothing as a model of a chromosome.

California Content Standards (http:/ www.cde.ca.gov\board\board\html):
2b. Students know that sexual reproduction produces offspring that inherit half their
genes from each parent. During fertilization, the egg and sperm cells combine their
single sets of chromosomes to form a zygote containing two sets, or the diploid
number of chromosomes for a species.
2d. Students know plant and animal cells contain many thousands of different genes and
typically have two copies of every gene. The two copies (alleles) of the gene may or
may not be identical, and one may be dominant in determining the phenotype while
the other is recessive.
2e. Students know that DNA (deoxyribonucleic acid) is the genetic material of living
organisms and is located in the chromosomes of each cell.

General Goals:
Students will understand concepts such as homozygous and heterozygous, genotype and phenotype, and dominant and recessive genes.
Specific Goals:
1. Students will describe and differentiate chromosomes and genes.
2. Students will identify the relationship between genotype and resulting phenotype.
3. Students will differentiate dominant and recessive genes.
4. Students will predict the possible genotypes and phenotypes produced from various genetic crossings.

Teaching Strategies:
1. Students will view chromosome model and brainstorm observations about the structure of a single chromosome and homologous chromosomes.
2. Students will discuss dominant and recessive genes and their relationship to phenotypes.
3. Students will predict the possible genotypes and phenotypes produced from various genetic crossings through independent practice.

Materials Needed:
Phase One - Chromosome Model
2 blue jeans - identical colors 2 socks - identical colors
2 shirts - different colors 2 boxer underwear - different colors
2 gloves - identical colors 10 large safety pins

Phase Two - Phenotype and Genotype and Genetic Crossings
4 blue socks, 3 white T-shirts
4 white socks, 3 blue T-shirts

Activities (step by step procedure) and Teaching Strategies:

Phase One - Chromosome Model
1. A model of a chromosome will be made prior to the lesson by attaching one of each of the clothing items (sock, glove, jean, boxer underwear, shirt) together with safety pins. The entire string of clothing will represent a chromosome. The individual garments will represent gene segments along the chromosome. A second chromosome will be constructed containing the same types of clothing placed in the same order.
2. Hand out “Jeans To Genes” Observation Sheet
3. Call on two student volunteers to display the first chromosome model to the class.
4. Ask students to record their observations of the single chromosome. Is the chromosome the same throughout? Call on volunteers to share their observation.
Explain that the entire chain of clothes represents a chromosome and that the individual garments represent genes. Although we can not see an individual’s genes, we can see the traits that they control (phenotype). For instance, the “glove” gene may control the shape of our fingers and the “Jean” gene the hair on our legs.
6. Call on two more student volunteers to hold up the second chromosome. Explain that two chromosomes are modeled because our chromosomes are paired. One we receive from our mother and the other from our father.
7. Ask students to brainstorm and record similarities and differences between the two chromosomes.
8. Students will then be asked to make observations about the chromosome models by answering directed questions. Students should note that the two chromosomes are similar because each contain the same number and types of genes. In addition, the genes are in the same order and located in the same place on each chromosome. Students should note that some genes are identical, while others, although they control the same trait, are different.
9. Introduce the terms homozygous and heterozygous. Explain that genes that are identical are called homozygous. Genes that control the same trait but are different are called heterozygous.
10. Check for comprehension by asking students to list all homozygous and heterozygous genes illustrated by the models on their observation sheet.

Phase Two - Phenotype and Genotype
1. Tell students that we will now focus on only one gene located on the chromosome model; the sock gene. Students will be given a hypothetical scenario. Tell students to imagine that these genes belong to a certain type of blackbird. Some blackbirds have white chests and some have blue chests. The sock gene will control chest color.
2. Demonstrate genotype and phenotype by selecting a student volunteer. Ask the student to hold two white sock genes in each hand and drape a white T-shirt over his/her shoulders.
3. Explain that the socks represent the birds genes. These two genes are located in the DNA of the bird and are referred to as the birds genotype.
4. Explain that although we can not see the actual genes inside a cell, we can see the expression of the genes which is the white chest (illustrated by the white T-shirt). Tell students that this physical expression of the genes is referred to as the phenotype.
5. Select two additional student volunteers. The second student will be handed two blue socks and wear a blue T-shirt to illustrate a blue phenotype.
6. Issue the last student volunteer one blue and one white sock and a white T-shirt. Explain that some genes are stronger than others. These genes called dominant genes mask the weaker genes called recessive genes. In this case, white is dominant.

Genetic Crossings (This lesson provides an introduction and transition to the study of heredity and punnett squares.)
1. Call on three student volunteers. Inform the class that the first volunteer will represent the mother blackbird. Have this student hold two white socks, one in each hand. Check for comprehension of parts one and two by asking students if this represents a homozygous or heterozygous genotype. Also, ask students what phenotype this bird would have. After students have responded, drape a white T-shirt over the student volunteer representing the mother bird.
2. The second volunteer will represent the father blackbird. Issue this bird two blue socks and a blue shirt.
3. Explain to students that although all of our body cells have two genes for every trait, only one gene is donated in the creation of the sperm and egg cells. This can be illustrated by placing one sock from the mother bird into a poster board with a picture of an egg cell and one sock from the father bird into a poster board with a picture of a sperm.
4. Explain that the donation of the gene from the gene pair by the parents is random. However, since both parents are heterozygous, mother will always donate a white and father will always donate a blue.
5. Have the third student represent the baby bird. Using the sock model and student volunteers, the class will predict possible offspring gene pairs (genotypes) and resulting phenotypes.
6. Repeat this procedure for the various genetic crossings indicated on observation sheet. Have students record possible phenotypes and genotypes of offspring from these crossings on observation sheet.

"Teacher Double Feature"
A competitive grant opportunity provided through a partnership between the Contra Costa County Office of Education and Pacific Bell.

Contra Costa County Office of Education
77 Santa Barbara Rd.
Pleasant Hill, CA 94523

May 2002