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Pedigrees
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Pedigrees are charts that are used to study the inheritance of a trait within a family, or on
a larger scale, within a closely related population. Pedigrees have been commonly used
when dealing with breeds of animals (cats, dogs, horses, and cattle), but are also
increasingly useful for zoos to prevent inbreeding within the zoo populations of a species
scattered about the world. In humans, pedigrees are especially useful in determining
which members of a family may have a disease, and also in determining the odds that a
couple will have a child with a birth defect.
Pedigrees are useful in showing the information known about individuals within a family,
and with the collection of enough information, can help deduce the genotypes of each
family member. As a standard, squares represents males and circles represent females.
Squares and circles that are shaded in represent individuals affected by the studied
condition. White or clear squares and circles represent unaffected individuals.
Occasionally, you will find a chart with circles and squares that are filled with gray (or
with a large central dot). These represent people who are unaffected by the condition but
are still carriers of the allele (heterozygous). A straight horizontal line between a male
and female represents a "marriage" or mating line. A vertical line descending from a
marriage line represents the offspring of the parents.
I
II
Pedigree Problem 1.
The pedigree below is studying the incidence of blonde hair in a family. In humans, dark
hair (B) is dominant to blonde hair (b). In this case, individuals who are shaded in are
homozygous recessive (blonde). Individuals who have clear circles and squares have
brown hair and at least
one dominant gene.
I
II
What are the EXACT genotypes of persons I-A, I-B and II-C through II-F above?
Pedigree Problem 2:
A man and a woman marry and have three children, two boys and one girl. When the
little girl turns one, she is diagnosed with Tay Sachs disease, a recessive, lethal disorder.
The boys, when they got older, decided to be tested, and it was determined that
fortunately they are not carriers. Draw the pedigree below, labeling each member of the
family with their possible genotype in regards to Tay Sachs disease.
Pedigree Problem 3:
Below is a pedigree for an inherited lung disease that is coded for by a dominant
allele. Provide the genotypes of each of the individuals marked with lower case letters.
I-a_________ I-b_________ II-c_________ III-d__________ II-e_________
I
II
III
Pedigree Problem 4:
Below is a pedigree for an inherited lung disease that is coded for by a recessive
allele. Provide the genotypes of each of the individuals marked with lower case letters.
I-a______
I
II
III
I-b_______
II-c______ III-d________
Pedigree Problem 5:
A man and woman marry. They have five children, 2 girls and 3 boys. The mother is a
carrier of hemophilia, an X-linked, recessive disorder. She passes the gene on to two of
the boys who died in childhood and one of the daughters is also a carrier. Both daughters
marry men without hemophilia. Draw the entire pedigree below:
What is the chance that the carrier daughter and her husband will have a child with
hemophilia?_____________
If these two parents have a boy, what will the chances be of this boy having
hemophilia?______
What is the change the daughter who is normal will have a child with hemophilia?_____