Notes: Tracing Traits using Pedigree Charts
Shaded symbols are persons showing the trait,
whether it’s dominant or recessive.
Name: ________________________________________________
Half-shaded symbols represent persons who are
carriers or heterozygous for the trait.
A Pedigree chart traces the inheritance of a particular trait through
several generations. It is most often used by genetic counselors to
help families determine who carries a particular trait of interest.
Circle with dot:
X-linked carrier –always female
Step 1: A genetic counselor will first gather information regarding who
the family members are and how are they related. This will go
back a few generations.
A diagonal line through a symbol means the
person is deceased.
Step 2: The genetic counselor will then ask who in the family has the
trait of interest (shows the trait).
Step 3: The genetic counselor will use this information to construct a
Pedigree chart, with all the family members’ names written
below each symbol.
Step 4: The genetic counselor will shade in the family members
showing the trait of interest. From there, the genotypes of all
individuals are determined by looking at the patterns of
inheritance from generation to generation.
Pedigree Key
What is a sex-linked trait?
 Genes located on the X chromosomes (some cause diseases)
 The Y is much smaller, contains few genes (Y is wimpy)
 Sex Linked Disorders
– Color Blindness (red-green)
– Hemophilia ("bleeders disease)
– Duchenne Muscular Dystrophy (weakening/loss of
skeletal muscles)
 More common for males to display disorders
Punnet Square- Hemophilia example
Squares represent males. Circles represent females.
I.
A horizontal line represents a marriage or mating
A vertical line extending down from the mating
line represents offspring.
II.
Roman numerals to the left of the pedigree show the generations.
Birth Order: children are listed in birth order with oldest on the far left.
How do you find the genotypes of the people in the chart?
a. Start with a person showing the trait. Look at his/her parents.
b. Decide what the parent’s genotypes would have to be to have
offspring with this genotype.
Identical Twins branch off of the
the same point, but are also
connected to each other.
Fraternal Twins only branch
off of the same point
c. If there is not enough information to figure out a genotype, then a
question mark is used to take the place of the uncertain allele.
Ex. _T?_
Answer the questions using the pedigree below.
Example:
A
Shaded = deaf
I.
Steve
Nancy
(D) is normal hearing
(d) is deaf
B
C
II.
Shaded = albinism
(A) is normal
(a) is albino
D
Alan
A. Is deafness a dominant or recessive trait? __________________
B. To be deaf, what genotype does this son have to have? ________
E
F
G
H
C. For two parents who have normal hearing to have a deaf son, they
must both be carriers. What is the parents’ genotype? __________
D. Write the genotypes for the parents and son under the correct
shape and half-shade any carriers.
Practice:
1. Draw a pedigree that represents Mary, who married Greg, and had
2 sons and 1 daughter. Their oldest son, Josh, married April and
had Ian (a boy) and Iris (a girl). Their middle child, Amy, married
Scott and had identical twin boys, Brandon and Bradley. Their
youngest, Zach, has not married.
Albinism is a genetic disorder in which a person
does not produce the brown pigment melanin.
2. Label the three generations with Roman Numerals.
3. How many albinos are there in the 3rd generation? ________
4. Write the genotype of each individual under their symbol.
5. What is the gender and genotype of individual D? ______________
Be sure to use the correct shapes (in the correct order) and
connecting lines. Then label each shape with the name of the
person it represents.
6. Half-shade those individuals that are heterozygous / carriers.
7. Is it possible for individual H to have a normal child? _________
Explain.________________________________________________
______________________________________________________
8. Add the following individuals to the pedigree above:
Individual E marries a homozygous dominant individual. They
have two children: a normal male and an albino female.
(Be sure to use the correct shapes and connecting lines. Then write
the genotypes below each shape and shade appropriately.)
Pedigree Problems
Name: __________________________________________
Period: ______
Date: ________________________
PROBLEM # 1: The pedigree below shows the recessive trait for nearsightedness in Jane’s family. Jane, her parents, and her brother all have
normal vision. Use N for the dominant allele and n for the recessive allele.
1. How many generations are represented in this pedigree? _________
1
2
2. How many children did the first couple (1 & 2) have? _____________
3. How many marriages are shown on this pedigree? _____________
3
4. What is the sex and genotype of individual # 2? _______________________________
4
5
6
5. What are Jane’s possible genotypes? ______________________
6. What is the genotype of individual 5? _______
7
8
Jane
7. What is the genotype of individual 6? _______
8. What is the probability that individuals 5 & 6 will have a child that is nearsighted? _______________________________________________
PROBLEM # 2: Earlobes in humans are either attached (dark shapes) or detached. Answer the following questions based on the pedigree below.
Use F for the dominant allele and f for the recessive allele.
9. Which trait is dominant, attached or detached earlobes? ____________________
1
10. What is the genotype of individual 1? ___________
2
3
4
9
10
11. What is the genotype of individual 2? ___________
12. What is the genotype of individual 4? ___________
5
6
7
8
13. What is the genotype of individual 8? ___________
14. What is the genotype of individual 9? ___________
15. If individual 12 marries a heterozygous individual, what is the probability that they
will have a child with attached earlobes? _______________
11
12