Face Lab Instructions
Introduction
Heredity is the passing on of traits, or characteristics, from parent to offspring. The units of heredity are called genes. Genes are found on the chromosomes in a cell. The combinations of genes for each trait occur by chance. When one gene in a pair is stronger than the other gene, the trait of the weaker gene is masked, or hidden. The stronger gene is the dominant gene~, and the gene that is masked is the recessive gene. Dominant genes are written as capital letters and recessive genes are written as lowercase letters. If both genes in a gene pair are the same, the trait is said to be homozygous, or pure. If the genes are not similar, the trait is said to be heterozygous, or hybrid. Sometimes genes are neither dominant nor recessive. The result of such a situation is a blending of traits. The genetic makeup of an individual is known as its genotype. The observable physical characteristics of an individual that are the result of its genotype are known as its phenotype. In humans, the sex of an individual is determined by the particular combination of the two sex chromosomes. Individuals that have two X chromosomes (XX) are females, whereas those with an X and a Y chromosome (XY) are males. In this investigation, you will observe how the results of different gene combinations produced certain traits.
Materials (per pair of students): 2 coins, 1 pencil, colored pencils, and sample face sheet
Procedure
1. Determine which partner will toss for the female and which will toss for the male. Remember that there are two genes per trait for most human traits.
2. Have the partner who is representing the male flip a coin to determine the sex of the offspring. If the coin lands heads up, the offspring is a female. If the coin lands tails up, the offspring is a male. Record the sex of the offspring on the face shape sheet provided.
3. For all the coin tosses you will now make, heads will represent the dominant gene and tails will represent the recessive gene.
4. You and your partner should now flip your coins at the same time. Note: The coins should be flipped only once for each trait, except for the traits describe in Procedures 6-8 which require multiple coin tosses .
5. Continue to flip the coins for each trait listed in the table in Figure 1. After each flip, record the trait of your offspring selected by the coin toss(es)by circling the trait selected by the coin toss(es).
6. Skin color is determined by 4 gene pairs, so it will be determined by making 4 tosses of the 2 coins. The darkness of your child’s skin color will be determined by the total number of heads you get after 4 tosses.
8 heads = very dark black 5 heads = dark brown 2 heads = very light brown
7 heads = dark black 4 heads = medium brown 1 head = light tan
6 heads = very dark brown 3 heads = light brown 0 heads = albino
7. Eye color is determined by 3 gene pairs, so it will be determined by making 3 tosses of the 2 coins. The darkness of your child’s eye color will be determined by the total number of heads you get after 3 tosses.
6 heads = dark brown 4 heads = light brown 2 heads = blue-green 0 heads = light blue
5 heads = brown 3 heads = hazel 1 head = blue
8. Hair color is determined by 4 gene pairs, so it will be determined by making 4 tosses of the 2 coins. The darkness of your child’s hair color will be determined by the total number of heads you get after 4 tosses. Eyebrows and eyelashes should be the same color as th hair color.
8 heads = black 5 heads = light brown 2 heads = very light brown
7 heads = dark black 4 heads = red 1 head = light tan
6 heads = brown 3 heads = dark blond 0 heads = albino
9. Using the recorded traits, draw the facial features for your offspring at age 16 on the face shape sheet provided (either round or square face shape – depending on your coin toss).
