Name:______Date:______Period: ____
Do Your Ears Hang Low?
Human Inheritance Activity
Background: Using the laws of heredity and probability, biologists have learned about the genetics of many human traits. In many of these traits several genes are involved and the pattern of inheritance is complex. For this activity we will assume that only two genes regulate the traits we are studying. Knowledge of your own traits and genetic make-up can give you information about the genetic makeup of your parents and possibly your brothers and sisters.
As you know we have two genes for each characteristic in our bodies. Sometimes these genes work together to determine what we look like and other times one gene takes over and overrules the other to determine a characteristic. The gene that takes over is called the dominant gene, while the gene that gets overruled is called the recessive gene.
Two terms that are important for this activity are genotype and phenotype. A genotype is a representation of the actual genes that an organism has for a particular characteristic. Since each trait has two genes you will use two symbols to represent this. Each trait has a different symbol. Dominant genes are represented by capital letters while recessive genes are represented by small letters. A homozygous genotype consists of two dominant genes or two recessive genes, while a heterozygous trait has one dominant gene and one recessive gene. A phenotype is the appearance of the organism for a certain characteristic.
Procedure:
1. Answer the pre-activity questions 1st.
2. Determine your phenotype for a characteristic by choosing the description that best matches your
phenotype and fill in the appropriate column.
3. If you have a dominant phenotype, there is no way to tell if you are homozygous or heterozygous for
this trait from this lab. So, write BOTH possible genotypes given in the appropriate column.
4. If you have a recessive phenotype for a characteristic, fill in the homozygous recessive genotype in the
appropriate column.
5. Answer the questions that follow.
Pre-activity Questions: Define the following terms.
1. dominant: ______
2. recessive: ______
3. phenotype: ______
4. genotype: ______
5. homozygous: ______
6. heterozygous (or hybrid): ______
Do Your Ears Hang Low?
Characteristic / Phenotype / PossibleGenotype(s)
1. TONGUE ROLLING à Can you roll your tongue into a U shape (like a taco shell)? If so, you are dominant for this trait. If you cannot roll your tongue into a U shape, you are recessive for this trait. (R or r)
2. EARLOBES à It is a dominant trait to have earlobes that hang down (free). A person who has earlobes attached directly to the side of his/her head is recessive for this trait. (L or l)
3. EARBUMP à Some people have a bump, called Darwin’s ear point, on the inside rim of the upper part of the ear ridge. If you have the bump it is due to the presence of a dominant allele. If you are lacking the bump you are recessive for this trait. (B or b)
4. WIDOW’S PEAK à If your hairline forms a downward “V” in the middle of your forehead, you have a widow’s peak. (i.e. Eddie Munster, vampires) A widow’s peak is caused by a dominant allele. A straight or even hairline indicates you are recessive for this trait.(V or v)
5. HITCHIKER’S THUMB à People who can bend the last joint of their thumbs back to a 90 degree angle are dominant for hitchhiker’s thumb. Those who lack this ability are recessive for this trait. (H or h)
6. POLYDACTYLY à If you were born with more than 5 fingers or toes on either of your hands or feet, you possess a dominant trait for polydactyly. Having 5 fingers and toes is a recessive trait. NOTE: In the US, people with extra toes and fingers usually have them removed shortly after birth. (P or p)
7. SYNDACTYLY à Having webbed fingers and toes is a dominant trait. Sometimes only a pair of fingers or toes is webbed. If you have fingers and toes that are separated from one another, then you are recessive for this trait. (S or s)
8. CLEFT CHIN à If you have an indentation in the middle of your chin you have a cleft chin. (i.e. John Travolta) A cleft chin is a recessive trait. The absence of a cleft chin is a dominant trait. (C or c)
9. HAIR WHORL à Ask a friend to look at the back of your head to determine if your hair whorls to the right (clockwise) or to the left (counterclockwise). A clockwise whorl is a dominant trait; a counterclockwise whorl is a recessive trait. (W or w)
10. DIMPLED CHEEKS à If you were born with dimples in either of your cheeks, you possess a dominant trait for dimpled cheeks. Having cheeks that are not dimpled is a recessive trait. (D or d)
11. VISION à If you have normal vision (20/20) you possess a dominant trait. If you are nearsighted (you can’t see far away) then you are recessive for this trait. (S or s)
12. EYE COLOR à If you have any color eyes besides blue, you possess a dominant trait for eye color. Having blue eyes is a recessive trait. (B or b)
13. MID-DIGITAL HAIR à If you have hair on the back middle part of any of your fingers you possess a dominant trait for mid-digital hair. If you lack hair on this part of any of your fingers then you are recessive for this trait. (M or m)
14. PTC/SBT PAPER à Taste the paper your teacher gave you. PTC or sodium benzoate paper is used as a diagnostic tool in medicine. The ability to taste the chemical is a dominant trait. People who cannot taste this chemical are recessive for the trait. (T or t)
Questions:
1. For which traits do you have the dominant phenotype? (Just list the # of the characteristic)
______
2. For which traits do you have the recessive phenotype? (Just list the # of the characteristic)
______
3. For which traits do you know that you are homozygous? (Just list the # of the characteristic)
______
4. For which traits might you be homozygous or heterozygous? (Just list the # of the characteristic)
______
5. Do you think anyone in the class has all the same traits as you? Why or why not? ______
______
______
6. If an individual does not have the ability to roll his/her tongue over, yet both of the individual’s parents do have this ability, what must be the parent’ genotype for this trait?
______
7. Is it possible for a mother and a father who each have five fingers on each hand to have a baby with six fingers? Why or why not?
______
8. A girl has blue eyes unlike her mother who has brown eyes. For this trait, what must the genotype of the girl be? The mother? What could the genotypes of the father be?
______