How to make a Pedigree Chart?
Genetic counseling provides information and counseling to couples who wish to
have children but are worried that they might pass a disease to their children.
Genetic counselors often make use of a diagram known as a pedigree, which
is a tool for tracing a trait through generations of a family. By making a
pedigree, it is often possible to predict whether a person is a carrier of a
heredity disease.
When you look at the chart note that:
Females are circles, males are squares.
Completely filled in circles or squares are affected, which means they have the trait you are
mapping.
Half-filled in circles or squares are carriers, which mean that they have one copy of the allele, but
not the trait. NOTE: Carriers are not always indicated on a pedigree. BUT it will always
accurately depict who has, and who does not have the disease.
Each Generation gets its own line with the oldest at the top.
Notice that siblings are connected with a line above their shape. Spouses are connected with a line
in the middle of their shape.
Practice problems (be careful..carriers are NOT shown)
Pedigree 1: The following is the pedigree of a disease that is controlled by a dominant
autosomal allele.
1. How many generations are shown in the pedigree?
2. How many individuals have at least one allele for this disease?
3. Can a carrier exist for this disease? Why or why not?
Pedigree 1
4. Do both male and female get the disease? Does it skip generations?
Pedigree 2: ???
1. Is this gene X-linked? How can you tell?
2. What illustrates that this trait is a recessive allele?
3. Is the father of the 3rd generation a carrier? Explain.
Pedigree 2
4. What is the likelihood that the individual in generation 3 that exhibits the disease will
have offspring with the disease if her husband is heterozygous for the trait? Include your
punnett square
Pedigree 3: ???
1. For each family member, write the alleles he or she has inherited for color vision
below the circle or square on the pedigree. Be careful! It’s Sex-linked!
Use these symbols:
XC represents a dominant allele for normal color carried on the X chromosome.
Xc represents a recessive allele for the trait carried on the X chromosome.
Y represents the chromosome inherited from a child's father. It carries no allele
for this trait.
2. One of the two brothers with normal color vision in the third generation of this
pedigree (lower right) has a colorblind son and two daughters with normal vision. What
must the genotype of his wife be? Add this marriage and their children to the pedigree.
Use the appropriate symbols to designate marriage, children, gender, normal color vision,
carriers, and colorblindness. Write the alleles each family member has inherited below
the circle or square.
3. One of the carrier sisters in the third generation of the pedigree marries and has two
colorblind daughters. What is her husband's genotype? You must draw out the punnet
square below to receive credit.
Pedigree 4: ???
Shown below is a pedigree chart for the inheritance of achondroplasia a form of
dwarfism. Dark circles or squares indicate individuals with achondroplasia. Remember
Carriers are not ALWAYS indicated. Is the gene that causes this form of dwarfism a
recessive or dominant trait? How do you know?
Pedigree 5: Look at the pedigree at the bottom of the page. Carriers are not shown, only
those who have the disease.
1. How many sons did the original parents in this pedigree have?
2.
How many daughters did the original parents in this pedigree have?
3. What type of allele produces this disease? Dominant, Codominant or Recessive?
4. Is it an autosomal disease, or is it X-linked? How can you tell?
5. Based on where the disease occurs, shade in all individuals who you believe are
carriers.
Final Activity: Time to make your own pedigree.
Cystic fibrosis is an autosomal recessive disease. A couple knows they have a family
history of cystic fibrosis and goes to a genetic counselor to determine the chances of
passing on the disease. They have this information:
1. Marie (the woman) knows that her father and maternal grandmother both have the
disease.
2. Marie has two sisters and a brother.
3. Her brother is married to a healthy woman and has a son with the disease.
4. Jake (the man) knows that both his parents were healthy, but one of his two sisters
has the disease.
5. The second sister married a healthy man and both their children (son and
daughter) were born with the disease.
Begin by drawing the pedigree as with the information that you have above. If there is
question regarding a person’s genotype, place a ? in his/her box. Fill in all carriers to
make life easier.
Now determine the couple’s chance of passing on the disease. If there is more than one
possibility, give them the best and worst case scenarios.