Instructional Objectives:
Students will be able to describe and apply the Mendellian principles of genetics, which include dominance and recessiveness of genes. Students will demonstrate how two parents contribute genes and how those genes appear in their offspring.

Vocabulary, key words:
Genes, Alleles, Dominance, Recessiveness, Chromosomes, Genotype, Phenotype

Procedure:
Do Now (5 mins): Ask students to consider the following: Do you have a gap in your front teeth? Can you roll your tongue? Do you have a widow's peak? Are your earlobes free or attached?

Revisit Mendellian principles of genetics (10 mins): The basics of these principles should have been covered in an earlier class, using Mendel's pea-plant experiments as the core example. Stuents must understand the principles of dominance, recessivness, what an allele is and genotype & phenotype to do the activity. The class can review these principles through 10 minutes of whole-class discussion before doing a group activity (below).

Review & Summary (5 mins): The key points & definitions should be highlighted and visible on the board for reference during the following activity.

Class activity (25 mins): Students will design their own chromosomes and then intereract with other students (in pairs). Each pair will contribute a chromosome that has 5 traits on it. The offspring that would result from each chromosome pair is described in writing and by drawing. Because each student pairs with many other students in the class, a large variety of offspring will surface. See below for a full description of this activity.

Review & Summary (5 mins): Once each student has paired with every other student, the resulting drawing and description of the offspring should be pinned onto a wall for comparison. The class will get a lot of laughs from the pictures and be able to check the accuracy of the phenotypes based on the combination of alleles. The teacher can randomly select 5 or so for the class to evaluate.

Activities:
Ideally, students should be seated in rows, with 2 students per table, but other seating arrangements will work also. Each student must be numbered 1 or 2.

Each student is given an index card which will serve as a chromosome. Each chromosome has 5 traits pre-printed on it (or the kids can copy this off the board) as follows:
1 = Gene for eye color:
2 = Gene for hair color:
3 = Gene for hair texture:
4 = Gene for dimples:
5 = Gene for height:

At the teachers instruction, each student will write in a chosen allele (a specific gene for each trait) for each of the 5 genes. For example, a student may choose:

1 = Gene for eye color: BLUE
2 = Gene for hair color: BROWN
3 = Gene for hair texture: CURLY... etc

The teacher should display on the board and point out that certain genes (alleles) are dominant over others. For example, brown eyes are dominant over blue eyes, so any offspring with a brown-eye gene will have brown eyes, even if the other gene contributed is for blue eyes.

Then, in 2 minute intervals (the teacher can blow a whistle to indicate the next move) each student numbered '2' must get up, move to the next table (where a number '1' is seated) and compare chromosomes. Based on the chromosome pair at that table, what will the offspring look like? Are there 2 dominant genes, one dominant and one recessive, or 2 recessive genes? Students must write the gene combination, describe the phenotype (physical characteristics) and draw the offspring.

Student should continue to move from table to table until every number 2 student has paired their chromosome with each number 1 student. The resulting drawings can be posted on the wall and compared (they will also provide a lot of amusement!).

Extension:
The student's chromosomes and offspring can be kept for a future class in which other Mendellian principles are covered. For example, incomplete dominance or codominance can be taught, and students can use their chromosomes and resulting offspring as the basis for exploring these principles. An activity where more genes are added and new offspring are made is an option.

Homework:
Look at everone in your immediate family and describe them in terms of the 5 traits we used in today's activity. Include your mother, father and any siblings. Then, for each person, write the possible gene cominations that they may have received from their parents. For example, if your dad has blue eyes, both of his parents must have given him an allele for blue eyes, since blue-eye alleles are recessive. But, is it possible that his parents had brown eyes? Yes, because they may have each had one recessive allele for blue eyes and one dominant allele for brown eyes.

Standards:
Students will understand and apply scientific concepts, principles and theories pertaining to the living environment.


Tips:
Cover the basics of genetics in an introductory class and use this class as a review and application session.

This class is designed for a 1-hour block scheduling class but can be adapted to a 42 minute class by using 2 class periods.

Preprinted index card 'chromosomes' and worksheets for the students to draw and describe their offspring will also come in handy.