Determining Genotypes from Phenotypes
Name
Period
Introduction
In this lab, you will determine some of your own phenotypic traits. For some of these traits, you
will be able to determine your genotype. If your trait is dominant, you will not be able to tell if you
are homozygous dominant or heterozygous. If your trait is recessive, you will know that you are
homozygous recessive. Some traits show incomplete dominance, meaning a heterozygous individual
will have a phenotype in between the two homozygous phenotypes. If the trait is controlled by
incomplete dominance, you can tell if you are homozygous or heterozygous. You will compare your
phenotypes and genotypes with others in the class. Given the almost limitless number of gene
combinations, it is almost impossible that anyone would have all the same traits as you.
Procedure
1. Pair up with someone and help each other to determine each of your phenotypes for the following
traits.
thumb
ear lobe
eyelash length
tongue rolling
PTC taste
lip protrusion
hairline
lip thickness
hair texture
inter-eye distance
2. Complete Table 1.
Results
1. Which traits do you have that are dominant?
2. Which traits do you have that are recessive?
3. Which of your traits are governed by incomplete dominance?
4. Which of your traits do you share with one or more of your classmates?
Table 1. Human Phenotypes and Genotypes
Traits
Dominant
Your Phenotype
Recessive
Hairline
Widow’s peak (WW/Ww)
Straight line
(ww)
Ear Lobe
Free (AA/Aa)
Eyelash
length
Tongue
dexterity
PTC Taste
Long (EE/Ee)
Attached
(aa)
Short (ee)
Thumb
Hitchhiker’s thumb (HH/Hh)
Lip
Thickness
Thick (LL/Ll)
Hair texture
Curly (HH)
Wavy (HS)
Inter-eye
distance
Close
together
(DD)
Protruding
(PP)
Medium
distance (DF)
Straight
(SS)
Far apart
(FF)
Slightly
protruding
(PN)
Not
protruding
(NN)
Lip
protrusion
Can roll (RR/Rr)
Taster (TT/Tt)
Your possible
genotypes
Unable to
roll (rr)
Non-taster
(tt)
Straight
thumb
Thin (ll)
Conclusions
1. What determines your traits?
2. With knowledge of the phenotype of a human, how can a person’s genotype be determined?
3. Does being dominant necessarily mean that an allele is more common in a population? Explain.