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Name:___________________ Date:_________ Class: ________
Using Phenotype to Determine Phenotype
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.
Knowledge of your own traits and genetic makeup can give you information about the
genetic makeup of your parents, and perhaps your brothers and sisters.
PROCEDURE & OBSERVATIONS:
Phenotypes & Genotypes for Common Traits
You will determine your phenotype and try to determine your genotype for the traits
listed in Table 1.
Remember, a dominant allele is written using a “C”apital letter while a recessive allele is
written using a “l”ower case letter. If you have a dominant phenotype you may be
homozygous or heterozygous. If you know that one of your parents has the recessive
phenotype, you must be heterozygous. If you are unsure of your parents’ phenotype, fill in
a minus sign (-) for the second gene.
If you possess the recessive phenotype, record it as two recessive genes.
1. Free earlobes are dominant (FF or Ff), while attached earlobes are recessive (ff).
Have your partner check your earlobes.
2. Inheritance of eye color is controlled by multiple genes, but people with the
homozygous recessive genotype (bb) have blue eyes. People with a dominant
genotype (BB or Bb) have different shades of brown, hazel, or green eyes.
3. 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
gene (w).
4. A dominant gene (R) gives some people the ability to roll their tongues into a "U"
shape when it is extended. People with recessive genes (rr) cannot roll their
tongues.
5. Individuals with curly hair have the dominant gene (C). Those with straight hair
have the recessive genes (cc).
6. Individuals who have hair on the middle joints of their fingers have the dominant
genotype (HH or Hh). Those with the recessive genotype (hh) do not have hair on
the middle joints of their fingers.
7. Inheritance of hair color is controlled by multiple genes, but people with the
homozygous recessive genotype (dd) have blonde or red hair. People with the
dominant genotype (DD or Dd) have different shades of brown or black.
8. Long eyelashes are the result of the dominant gene (L).
result of the recessive genes (ll).
Short eyelashes are the
9. Fold your hands together as demonstrated by your instructor. If your left thumb
sits over your right you possess the dominant gene (L). If your right thumb is on
top you possess the recessive genes (ll).
10. Fold your arms over your chest as demonstrated by your instructor. If your left
arm sits over your right you possess the dominant gene (L). If your right arm is on
top you possess the recessive genes (ll).
Table 1
TRAIT
1. Shape of ear lobe
2. Eye color
3. Shape of hairline
4. Ability to roll tongue
5. Hair Curliness
6. Hair on middle joint of fingers
7. Hair color
8. Eyelash length
9. Left thumb on top
10. Left arm on top
PHENOTYPE
GENOTYPE
Use you notes/textbook/netbook to
answer the questions below
1. The basic concepts of heredity were worked out in the mid 1800s by the Austrian
monk __________________________.
2. In crosses with organisms showing pairs of contrasting traits, one trait is usually
______________, while the other trait is ________________.
3. An organism with two like genes for a trait is ________________, while a hybrid,
with two unlike genes for a trait, is ___________________.
4. The physical appearance of an individual is its _______________.
5. The genetic makeup of an individual is its ____________________.
6. The units of heredity are _________________ and are located on the
_________________.
7. What did Gregor Mendel know about genes?
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8. Why is it difficult to determine the genotype of a person showing the dominant
phenotype?
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9. Why is it easy to determine the genotype of a person showing the recessive
phenotype?
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