Biology
Name___________
Lab: Determining YOUR phenotype and genotype for various traits
Review:
1. For each genotype below, indicate whether it is heterozygous (HET) or
homogeneous (HOM).
AA ____
Ee ____
Jj ______
ff _____
gg ____
Hh _____
2. For each of the genotypes below, determine the phenotype.
Purple flowers are dominant to white flowers
PP__________________________________
Pp__________________________________
pp__________________________________
3. For each phenotype, list the genotypes. (Remember to use the letter of the
dominant trait.)
Round seeds are dominant to wrinkled
__________ Round
__________ Round
__________ Wrinkled
Now you will determine some of your own phenotypic traits. From these, you will be
able to determine what your genotypes are for some of the traits. If a trait is dominant
and you possess that trait, you will not be able to determine your exact genotype
because you could be either homozygous or heterozygous for the gene. (On your chart
you will include the 2 possible genotypes) However, if a trait is determined by
incomplete dominance, you can tell if you are heterozygous or homozygous. Genotypes
of recessive traits are easily determined.
1. PTC Taster (P): Individuals who can taste the bitter chemical phenylthiocarbamide,
PTC, have at least one dominant allele. Those with the recessive genotype cannot
taste it. Taste the strip of control paper. Then taste the strip of PTC Paper to see if
there is a difference or not.
2. Mid-Digital Hair (H): Individuals who have hair on the middle joints of their fingers
have at least one dominant allele. Those with two recessive alleles do not have hair
on the joint.
3. Red hair (R): Individuals with red hair have the recessive genotype. Those with any
other color hair have at least one dominant allele.
4. Curly hair (C): Individuals having curly hair have at least one dominant allele.
People having straight hair have the recessive genotype.
5. Eye lashes (Y): Short eyelashes are the result of a recessive genotype. Long
eyelashes have at least one dominant allele.
6. Freckles (K): The recessive genotype means the individual lacks freckles. An
individual with freckles will have at least one dominant allele.
7. Dimples (D): An individual without dimples is homozygous recessive, while an
individual with dimples has at least one dominant allele.
8. Cleft Chin (M): An individual with a genotype of homozygous recessive will have a
cleft chin, while a person with at least one dominant allele will not have a cleft
chin.
9. Hitchhiker’s thumb (J): A person that can bend the last joint of the thumb to
approximately a 45 degree angle has the recessive genotype while an individual
that cannot do it has at least one dominant allele.
10. Index Finger Length (I): If the index finger is shorter than the ring finger (4th finger
next to the pinky), you have a dominant allele. If not, you have a recessive allele.
11. Ear lobes (E): Free ear lobes have at least one dominant allele. People with
attached earlobes are recessive.
12. Widow’s Peak (W): A hairline that forms a downward point in the middle of the
forehand is caused by a dominant allele. A smooth hairline is caused by a recessive
genotype.
13. Tongue roller (T): A dominant allele gives some people the ability to roll their
tongues into a “U” shape when it is extended. People with the recessive alleles
cannot roll their tongues.
14. Tongue folder (F): A dominant allele gives some people the ability to fold their
tongues over while sticking it out. People with the recessive genotype cannot.
15. Bent Little Finger (L): A dominant allele results in the end joint of the little finger of
each hand bending inward. Straight little fingers are a result of the recessive
genotype. Place your hands on a flat surface, palms down, and relax. Check to see
if the first joints of your little fingers are bent or straight.
Human Phenotypes and Genotypes
Traits
Recessive
Dominant
PTC taster
Taster
Non-taster
Mid-digital
hair
Hair on middle
joint
No hair on
middle joint
Red hair
All other hair
colors
Red hair
Curly hair
Curly
Eye lashes
Long
Short
Freckles
Freckles
No freckles
Dimples
Dimples
No dimples
Cleft chin
No cleft chin
Cleft chin
Hitch-hiker’s
thumb
Can not bend
90o
Can bend 90o
Index finger
length
Index finger
shorter than
ring finger
Earlobes
Free earlobes
Widow’s Peak
Widow’s peak
Tongue roller
Can roll
Index finger
not shorter
than ring
finger
Attached
earlobes
Smooth
hairline
Can’t roll
Tongue folder
Can fold
Can’t fold
Bent little
finger
Bent
straight
Wavy
(Cc)
straight
Your
phenotype
Your possible
Genotype(s)
Monohybrid crosses
Draw a Punnett square for each cross.
1. A person with attached earlobes is crossed with a person who is heterozygous for
unattached earlobes. What chances that their children will have attached or
unattached earlobes?
2. What offspring phenotypes would be expected in the following crosses:
a) Homozygous PTC taster X Heterozygous PTC taster
b) Non-taster X Heterozygous PTC taster
c) If Mr. and Mrs. McClure have 3 children and one of them is a non-taster, what
are the genotypes of Mr. and Mrs. McClure?