Lab 12 – Pedigree Analysis
Objectives


Draw and interpret pedigrees
Differentiate between autosomal recessive, autosomal dominant, and X-linked recessive
inheritance patterns
Introduction
Why do people look different from each other? Everyone has a face with the same basic
features. Yet even in the largest of crowds, it is unlikely that two people would look exactly
alike. Hair color, skin color, eye color, and facial features vary tremendously.
What causes this vast range of characteristics? Why do you look different from everyone
in your class, in your school, and almost everyone in the world? On the other hand, why do
some brothers and sisters, or even complete strangers, look extraordinarily alike? The answers to
all of these questions are related to the way genes are inherited and how they govern physical
traits.
New research has made it possible to understand more about the inheritance of human
traits and genetic disorders. The diagnosis and treatment of some genetic disorders are already
possible. If you ever have children or do have children now, understanding some of this
information may be important to you and your family.
In understanding the transmission of genes, the inheritance patterns of traits are
examined. Experiments are designed so that the transmission of traits from parents to offspring
can be analyzed through several generations. Patterns of inheritance are sought that will provide
insights into more general genetic principles. In the middle of the nineteenth century, Gregor
Mendel performed the first significant genetic experiments that have impacted the understanding
of heredity. Information derived from his work serves today as the foundation of transmission
genetics. In human studies, where designed matings are neither possible nor desirable, pedigree
analysis is used. In pedigree analysis, patterns of inheritance are traced through as many
generations as possible, leading to inferences concerning the mode of inheritance of the trait
under investigation.
A pedigree can illustrate the difference in patterns between an autosomal trait and an Xlinked trait. In today’s lab, you will learn the symbols of a pedigree and how they are connected
to show parents, offspring, siblings, and generations. Once familiar with the pedigree symbols,
you will draw and interpret some example family pedigrees.
1
Lab 12 – Pedigree Analysis
12.1 Pedigrees and genetic disorders
1.
Search the Internet for sites containing information about human pedigree symbols. One
possible site is http://www.uic.edu/classes/bms/bms655/lesson3.html although there is an
error with the monozygotic (=identical) twin symbol. Do you know what the error
is????
2.
In Table 1, write down the general symbols that are used when making a family pedigree.
Make sure you have symbols for at least the following: male, female, affected, mating,
related mating, deceased, female carrier for X-linked trait, carrier (heterozygous) for
autosomal recessive trait, identical twins, and nonidentical twins.
3.
When observing pedigrees, three major inheritance patterns are evident. A disorder can
be autosomal recessive, autosomal dominant, or X-linked recessive.
If a disorder is an autosomal recessive disorder, a person must have two recessive alleles
in order to have that disease. In Table 2, using the letters A and a, determine what
genotypes an affected, carrier, or normal person would have if the disorder is an
autosomal recessive disorder.
If a disorder is an autosomal dominant disorder, a person must have at least one dominant
allele in order to have that disease. In Table 2, using the letters A and a, determine what
genotypes an affected or normal person would have if the disorder is an autosomal
dominant disorder.
4.
5.
6.
Genes located on the X sex chromosome only determine a disorder that is X-linked
recessive. Females must have two recessive alleles in order to have an X-linked
recessive disorder while males only need one recessive allele in order to have an X-linked
recessive disorder. In Table 3, using alleles XN and Xn, determine what genotypes an
affected female, carrier female, unaffected female, affected male, and unaffected male
would have if the disorder is an X-linked recessive disorder.
7.
Answer additional questions on QUESTIONS pages.
2
Lab 12 – Pedigree Analysis
12.1 QUESTIONS
1.
Complete Table 1 below.
Table 1. Symbols used in pedigrees and their meanings. Include the following symbols: male,
female, affected, mating, related mating, deceased, female carrier for X-linked trait, carrier for
autosomal recessive trait, identical twins, and non-identical twins.
Male:
Related mating:
Identical twins
Female:
Deceased:
Non-identical
twins
Affected:
Female carrier for X-linked trait:
Mating:
Female/male carrier (heterozygote) for autosomal recessive trait:
2.
Complete Table 2 below.
Table 2. Genotypes of individuals who have autosomal disorders. Use the letters A and a.
Autosomal
Recessive Disorder
Affected
Carrier
Normal
3.
Autosomal
Dominant Disorder
/////////////////////////////////////////
Complete Table 3 below.
Table 3. Genotypes of individuals who have X-linked recessive disorders. Use XN = normal
allele and Xn = affected allele. Y chromosome has no X-linked allele.
X-linked Recessive Genotype
Normal female who is not carrier
Normal female who is carrier
Affected female
Normal male
Affected male
3
Lab 12 – Pedigree Analysis
4.
Martha and Stan (both unaffected) have four children, identical twin daughters and
identical twin sons, who are three years younger than the girls. Both of the daughters are
affected. One of the identical twin daughters, Jessica, marries John, and they have Josh
and Cindy, their “baby.” John, Josh, and Cindy are unaffected. Josh elopes with Mary
(unaffected). Years later, they have two children: the older son Nick has the disorder
while Tania is unaffected. Both sons of Martha and Stan are unaffected. One of Martha
and Stan’s twin sons, Rick, marries Madeline. Their eldest Trudy and middle child
Georgean are unaffected while the youngest Henry is affected.
Make a pedigree of the above family. Siblings are arranged with the eldest on the left
and going right to the youngest. Use appropriate symbols for carriers, when necessary.
5.
Suppose Rick and Madeline have another child. What is the chance that this child is
unaffected?
6.
What could Tania’s genotype be? If there is more than one possibility because there is
not enough information from the pedigree, write both. Use the letters A and a.
4
Lab 12 – Pedigree Analysis
7.
Color blindness is an X-linked recessive trait. The father is not color blind and neither is
the mother. Their eldest son George and middle boy are color blind, and their daughter
Ashley can see normally. George marries Nicole, who can see normally, and they have
two sons who are color blind. Nicole’s mom was color blind. Ashley marries a guy who
can see normally. They have 2 sons and young identical twin daughters. The younger
son is color blind.
Make a pedigree of the above family. Use appropriate symbols for carriers, when
necessary.
8.
If Ashley and her husband have another daughter, what is the chance that this daughter
would be color blind?
5
Lab 12 – Pedigree Analysis
9.
Jason (affected) has three children with Jasmine (not affected). The eldest Harry and the
middle child Beatrice are affected while Ryan is not. Harry marries a woman who is not
affected, and they have four children: fraternal twins (different sexes) (age 26), Tracy
(age 24), and Gina (age 23). Gina is affected. Beatrice and William (affected) get
together and have Troy (affected) and “Baby” Shane (unaffected). Troy and Gina,
though cousins, decide that they are in love and get married. They have a daughter Jill,
who is affected. Shane marries Eileen (affected), and they have three children: a
daughter who died early, a daughter who is affected, and their youngest son who is not
affected.
Make a pedigree of the above family. Because this family has an autosomal dominant
pattern of inheritance, no carriers are present.
10.
If Shane and Eileen have another child, what is the chance that this child would be
unaffected?
6