Tracing Traits
Have you ever wondered about traits that you inherited from
your parents? You know that traits are passed from
generation to generation, but do you have a trait that neither of
your parents has? In this project, you will develop a family
tree, or pedigree, similar to the one shown in the diagram
below. You will trace an inherited trait through your own family
or another family who can help you with the information you
will need. Next you will survey a family to determine some of
the traits they share. Finally, you will trace a trait to determine
how it has passed from generation to generation.
Materials
 Pencil
 paper
Procedure
1. The diagram at right
I
shows a family history
Grandparents
with four generations.
On a separate piece of
paper, draw a similar
II
diagram of the family
Parents
you have chosen.
Include as many family
members as possible,
III
such as grandparents,
Children
parents, children, and
grand children. Use
circles to represent the
IV
females in the family
and squares to represent
Grandchildren
the males. You may
include other
information if you wish, such as the family
member’s name, birthdate, or picture. Other
members of the family may be helpful in providing the information you need.
2. Draw a chart similar to the one on the next page. Survey each of the family
members shown in your family tree to determine which have the dominant
form and which have the recessive form of the trait described in the chart.
Ask them if they have hair on the middle segment of their fingers. Write each
person’s name in the appropriate square. Be sure to explain to each person
that it is perfectly normal to have either the dominant or recessive trait.
Dominant Trait
Recessive Trait
Hair is present on
the middle
segment of finger
(H)
Hair is absent on
the middle
segment of fingers
(h)
Family members
with the
dominant trait
Family members
with the recessive
trait
3. Trace the trait described in the chart throughout the family tree you
diagrammed in step 1. Do this by shading or coloring the square or circle
symbols or the family member who demonstrated the dominant form of this
trait. Leave the other symbols unshaded.
Analysis
4. What percentages of family members
demonstrate the dominant form of the trait?
Calculate this by counting the number of
people who have the dominant form of the
trait and dividing this number by the total
number of family members you surveyed.
Then multiply you answer by 100. An
example is done for you to the right
Example: Calculating percentages
10 people with trait = 1/2
20 people surveyed
1/2 = .50 x 100 = 50%
5. What percentages of the family members demonstrate the recessive form of
the trait? Why doesn’t every family member have the dominant trait?
6. Compare you percentage calculation for the dominant trait with the
calculations of you classmates. Are there some families with a higher
percentage of the dominant trait?
7. Choose one of the family members who demonstrated the recessive form of
the chosen trait. What much be the genotype of this individual? How did this
person get each of the alleles that make up his or her genotype? What are the
possible genotypes for the parents of this individual? Are there any brothers
or sisters? Do they show the dominant or recessive trait?
8. Draw a Punnett square similar to the one at the right. Use it to illustrate how
this person might have
inherited the recessive
trait. Inside the Punnett
square, write the
genotype of the person
you have chosen to
study in the bottom
right-hand corner. Try
to determine the
genotype of the parents.
HINT: There may be
more than one possible
genotype. Which allele
(dominant or recessive)
much have been passed
on from a parent if there is a brother or sister who shows the dominate trait?
Father
Mother
?
?
?
?