Demonstration: Inheritance of dominant and recessive traits.

We will study human heredity using the family tree (FT) board. Scientists have developed a standard notation that is used on this board for discussing heredity. The squares on this board represent males and the circles represent females. A horizontal line between male and female indicates marriage. A vertical line indicates their descendants. When there are more than one descendent it is shown as given in line F2 on the board.

As you look at the FT board, the top row makred P1 represents two couples whom we call parents. Their offspring are labelled F1. The four descendants of these two are labelled F2. These are the grandchildren of the P1 generation. The F2 generation shows four offspring. It represents a 25% probability that the F1 parents can have a child with the traits being studied. (These correspond to the four entries in the Punnett square discussed above.)
Genes, in this kit, are represented by plastic parts illustrating various facial traits. Each part shows the trait which is the effect of the particular gene. (The phenotype is shown on the board and not the genotype.)

Lesson 1:

On a small pallet, place 10 "brown eyes", 10 "blues" and 4 "H" labels. Have the students do these activities along with you using their worksheets and colored pencils. Line P1 on the Family Tree board represents the parents. Place two brown-eye traits into each male face along the P1 line. These male parents are both PURE brown in eye color. (Both genes in the pair are for brown eyes.)
Next, place two blue-eye traits onto each female face along P1. These female parents are both PURE blue in eye color. (Both genes in the pair are for blue eyes.) Now each couple has one child. Each parent contributes one gene for eye color to his or her F1 child. Remove a gene from each parent (P1) and place it onto the face of its offspring. (Place another gene similar to the one just removed onto the parent since each gene occurs in pairs.)

Place one additional brown and one blue onto each F1 parent. (This will give them enough genes to pass on to the next generation.) Now make the four possible offspring. Discuss the results. What are their eye colors? (3 brown, 1 blue) How many brown-eyed? (3) How many blue eyed? (1) How many hybrids? (2) Is their an equal chance to receive either gene? (yes) If these parents had four children, would they necessarily produce one blue-eyed child? (NO). (Lesson #2 will help the girls understand this.)

Lesson #2: Laws of chance
Tie the girls observations to the F2 offspring in the first lesson.

Lesson #3: Dominant Traits
The P1 line should show the first set of parents to be father, pure brown (BB), mother, pure blue (bb). The mother and father for the second set of parents should both be pure blue. This is the same as saying BB x bb and bb x bb. In this notation, males are always given to the left of the 'x' and females to the right. The uppercase letters (B) indicate a dominant trait. The lower case letters (b) indicate a recessive trait.
Have the students guess what the possibilities are for F1 and F2. Put the appropriate eyes on the board. The students should put the results on their worksheets.
There are 3 cases (2,3, & 4) in this lesson. Do as many as time permits