Name ____________________
Human Inheritance Lab
Regents Biology
Using the basic laws of heredity & probability, biologists have learned about the genetics
of many human traits. In many of these traits, several genes are involved & the pattern of
inheritance is complex. Most of the traits that are being studied in this activity are
regulated by only two genes. Knowledge of your own traits & genetic make-up can give
you information about the genetic make-up of your parents & perhaps your brothers &
sisters.
Part I: Your phenotype & Genotype for some common traits
Directions: Complete Data Table 1 by circling your phenotypic characteristic & using
the information provided below to try and determine your genotype for the traits listed in
the table. Remember if you have a dominant trait you may homozygous or heterozygous.
If you know that one of your parents has the recessive trait, you must be heterozygous. If
neither of your parents has the recessive trait, fill in a minus sign (-) for the second gene.
If you possess the recessive trait, record it as the two recessive genes.
a. Trait: earlobe attachment
Free earlobes are a dominant trait, L. People with earlobes attached directly to the
side of the head have the recessive genotype ll. Circle your earlobe phenotype &
record your earlobe genotype. (Remember if you have the dominant trait you may
not be able to determine whether you are homozygous or heterozygous. In that
case, record L- in the table.)
b. Trait: Eye color
Inheritance of eye color is controlled by multiple genes, but people with
homozygous recessive genotype bb, have blue eyes. People with a dominant gene,
B, have different shades of brown, hazel or green eyes. Circle your eye color
phenotype & record your eye color genotype.
c. Trait: Shape of hairline
A widow’s peak is a hairline that comes to a point in the middle of the forehead.
This is caused by a dominant gene, W. A smooth hairline is caused by the
recessive genes ww. Circle your hairline phenotype & record your hairline
genotype.
d. Trait: Ability to roll tongue
A dominant gene, R, gives some people the ability to roll their tongues into a “U”
shape when it is extended. People with the recessive genes, rr, can not roll their
tongues. Circle your tongue phenotype & record your tongue genotype.
e. Trait: Ability to fold tongue
A dominant gene, T, gives some people the ability to fold their tongues over.
People with the recessive genes, tt, cannot. Circle your tongue phenotype &
record your tongue genotype.
f. Trait: Shape of little finger
g.
h.
i.
j.
k.
l.
m.
n.
A dominant gene, F, results in the end joint of the little finger of each hand
bending inward. Straight little fingers are a result of the recessive genes ff. Circle
your finger phenotype & record your finger genotype.
Trait: Ability to taste PTC
Individuals who can taste the bitter chemical phenylthiocarbamide, PTC, have the
dominant gene, A. Those with the recessive genes, aa, cannot taste it. Obtain a
piece of PTC paper from your instructor and circle your tasting phenotype &
record your tasting genotype.
Trait: Hair on middle joint of fingers
Individuals who have hair on the middle joints of their fingers have the dominant
gene H. Those with the recessive genes, hh, do not have hair on that joint. Circle
your hair joint phenotype & record your hair joint genotype.
Trait: Hair color
Individuals with red hair possess the recessive genes, nn. Individuals with any
other hair color have the dominant gene, N. Circle your hair color phenotype &
record your hair color genotype.
Trait: Hair curliness
Individuals with curly hair have the dominant gene C. Those with straight hair
have the recessive genes cc. Circle your hair type phenotype & record your hair
type genotype.
Trait: Eyelash length
Long eyelashes are the result of the dominant gene S. Short eyelashes are the
result of the recessive genes ss. Circle your eyelash phenotype & record your
eyelash genotype.
Trait: Number of fingers
Some individuals are born with 6 or more fingers on each hand. This is a
dominant trait caused by the gene P. Individuals with 5 fingers on each hand have
the recessive genes pp. Circle your finger phenotype & record your finger
genotype.
Trait: Thumb type
Some individuals are born with a thumb that bends outward. This is a result of the
recessive genes, hh. Individuals without this trait have at least one dominant gene,
H. Circle your thumb phenotype & record your thumb genotype.
Trait: Skin pigmentation
Some individuals are born without the pigment melanin and appear albino. This is
a result of the recessive genes, dd. Individuals with normal pigmentation have at
least one dominant D. Circle your skin phenotype & record your skin genotype.
Table 1
Trait
Shape of earlobe
Eye color
Phenotype
attached
Brown
green
Widow’s
peak
Roller
Non-roller
Folder
Non-folder
Bent
straight
Taster
Non-taster
Hair
No hair
Shape of hairline
Free
Blue
Hazel
Smooth
Ability to roll tongue
Ability to fold tongue
Shape of little finger
Ability to taste PTC
Hair on middle joint of
fingers
Hair color
Hair curliness
Eyelash length
Number of fingers
Thumb type
Skin
Red
Curly
Long
5
Hitchhiker
Pigment
Genotype
Not red
straight
Short
6
Straight
No pigment
Part II: Human pedigree
A diagram showing the transmission of a trait through several generations of a family
is called a pedigree. In figure 1, generation I is made up of grandparents, generation II
is their children, & generation III is their grandchildren.
Directions: Study the pedigree diagram in Figure 1 to learn the symbols. Then
complete figures 2 & 3 based on the basic laws of inheritance & the information
provided.
Figure 1
Use D to represent the gene for normal skin, & dd to represent the genotype for
albinism. Where you cannot be sure whether an individual with the dominant
trait is heterozygous or homozygous, show the genotype as D-.
Figure 2
Individual
I
1
2
3
4
II
1
2
3
4
5
6
7
III
1
2
Genotype
Use A to represent the gene for PTC taster, a dominant trait. Use aa for the PTC
non-taster, the recessive trait.
Figure 3
Individual
I
1
2
3
4
II
1
2
3
4
5
6
7
8
III
1
2
3
4
Genotype
Part III: Your pedigree for a trait
Directions: Construct a pedigree diagram of your family for one of the traits listed in
Part I. Pick a trait that is not found in all the members of your family and list as many
genotypes as possible.
Questions
1. Do you think that anyone in your class has all the same traits that you have?
Why?
2. Which is the most common trait in your class?
3. Which is the least common trait in your class?
4. Would you expect the most common trait to be a dominant trait?
5. In what case could the most common trait be the recessive version?
6. In the pedigree in figure 2, if individuals 6 & 7 have another child, what is the
chance that it will be an albino?
7. In figure 2, are individuals 1 & 2 in generation I homozygous or heterozygous?
8. In the pedigree diagram in figure 3, if individuals 4 & 5 in generation II have
another child, what is the probability that it will be a taster?
9. In figure 3, if individual 8 in generation II married a man with genotype AA, what
is the probability that she will have a non-taster child?