NAME:______________________PERIOD:_____DATE:________
Lab: Human Genetic Traits
Directions: This exercise deals with the action of human genes on desecrate,
easily observable traits. You will make observations of these traits in yourself
and in your classmates to gain an understanding of how particular genes are
expressed in humans. These traits are known as single-gene traits, which are the
expressions of two alleles at one gene locus. Have another student check you for
each of the traits listed in the table below. Record in the table on the next page
your results. Under phenotype list if you are dominant or recessive for the trait
and under genotype list possible combinations of genes.
TRAIT
DOMINANT
RECESSIVE
Bent Pinky (B, b)
Last joint is bent
Last joint is straight
Skin Color (S, s)
Dark colors
Light colors
Freckles (F, f)
Present
Absent
Earlobe (E, e)
Unattached
Attached
Tongue Rolling (R, r)
Can roll edges of tongue
Widow’s Peak (W, w)
Present
Can’t roll edges of
tongue
Absent
Thumb Crossing (T, t)
Left thumb over right
Right thumb over left
Mid-Digital Hair (M, m)
Hair on mid-digit
No hair
Cleft Chin (C, c)
Indentation in middle
No indentation
Eyebrows (E, e)
Eyebrows not connected
Eyebrows connected
Hitchhiker’s Thumb (H, h)
Low degree angle
90-degree angle
Dimples (D, d)
Present
Absent
PTC Tasters (P, p)
Taster
Non-taster
Sodium Benzoate (S, s)
Taster
Non-taster
Thiourea (T, t)
Taster
Non-taster
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Your Genetic Traits
TRAIT
Phenotype
Genotype
Bent Pinky (B, b)
Skin Color (S, s)
Freckles (F, f)
Earlobe (E, e)
Tongue Rolling (R, r)
Widow’s Peak (W, w)
Thumb Crossing (T, t)
Mid-Digital Hair (M, m)
Cleft Chin (C, c)
Eyebrows (E, e)
Hitchhiker’s Thumb
(H, h)
Dimples (D, d)
PTC Tasters (P, p)
Sodium Benzoate (S, s)
Thiourea (T, t)
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Your Parents
Phenotypes
Mom
Dad
Class Results
TRAIT
DOMINANT
RECESSIVE
Bent Pinky (B, b)
Skin Color (S, s)
Freckles (F, f)
Earlobe (E, e)
Tongue Rolling (R, r)
Widow’s Peak (W, w)
Thumb Crossing (T, t)
Mid-Digital Hair (M, m)
Cleft Chin (C, c)
Eyebrows (E, e)
Hitchhiker’s Thumb (H, h)
Dimples (D, d)
PTC Tasters (P, p)
Sodium Benzoate (S, s)
Thiourea (T, t)
Questions:
1. How many dominant phenotype traits do you have? _______________
List which traits are dominant.
2. How many recessive phenotype traits do you have? _______________
List which traits are recessive.
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3. Are phenotypes for some traits clearly more abundant than the alternate
phenotypes for these traits? __________ Why do you believe this is true?
4. Some human traits can be changed by human intervention and some cannot.
Provide examples of each of these types of traits.
5. You probably already know that some traits are genetic and others are
environmental. But most human traits reflect an interaction between genetic and
environmental factors. Name some traits that might fall into this category and
explain why you think they do.
6. Describe some of the benefits of human genetic variation. What are some of the
potential problems that it can cause?
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