Download Pedigree Analysis Introduction Developing Conclusions About

Pedigree Analysis
Introduction
A pedigree is a diagram of family relationships that uses symbols to represent people and
lines to represent genetic relationships. These diagrams make it easier to visualize
relationships within families, particularly large extended families. Pedigrees are often
used to determine the mode of inheritance (dominant, recessive, etc.) of genetic diseases.
A sample pedigree is below.
In a pedigree, squares represent males and circles represent females. Horizontal lines
connecting a male and female represent mating. Vertical lines extending downward from
a couple represent their children. Subsequent generations are therefore written underneath
the parental generations and the oldest individuals are found at the top of the pedigree.
If the purpose of a pedigree is to analyze the pattern of inheritance of a particular trait, it
is customary to shade in the symbol of all individuals that possess this trait.
In the pedigree above, the grandparents had two children, a son and a daughter. The son
had the trait in question. One of his four children also had the trait.
In the exercises below, assume that the trait in question is a genetic disease or
abnormality. We will learn patterns of inheritance that have the following modes of
inheritance:
autosomal dominant
autosomal recessive
X-linked recessive
Developing Conclusions About Different Modes of Inheritance
Autosomal Dominant
1. The pedigree below is for a genetic disease or abnormality. We do not yet know if it is
dominant or recessive. We will determine if it is possible that the trait is autosomal
dominant. If the trait were dominant, we could use the following designations:
A = the trait (a genetic disease or abnormality, dominant)
a = normal (recessive)
a) Assume for the moment that the trait is dominant (we don't know yet). The pedigree
shows that three of the individuals have the recessive (normal) phenotype and one
individual has the dominant (abnormal) phenotype. Write the genotype of the affected
(abnormal) individual next to her symbol in the pedigree below. If you only know one of
the genes (letters), use a "?" for the unknown letter. If possible, write the genotype of the
three recessive individuals next to their symbols. As you attempt to write the genotypes,
keep in mind that the pedigree may not be possible for a dominant trait; it may not be
possible to write the genotypes.
b) Is it possible that the pedigree above is for an autosomal dominant trait? To answer
this question, you need to know that the affected individual is "A?". She received one
gene from each parent. Therefore at least one parent must have the "A" gene. As you can
see, neither of the parents have the gene because their symbols indicate that they have the
recessive phenotype (their genotype is aa). The pedigree is not possible; it is not for a
dominant trait.
c) Write the genotypes next to the symbol for each person in the pedigree below
assuming that it is for a dominant trait.
d) Is it possible that this pedigree is for an autosomal dominant trait?
e) What can you conclude from these two examples about the parents of a person that has
a dominant characteristic? (Circle the correct answer below.)
--If a person has a dominant trait, the parents will not have the trait.
--If a person has a dominant trait, the parents might have the trait or they might not have
it.
--If a person has a dominant trait, at least one of the parents will have the trait.
--If a person has a dominant trait, both of the parents will have the trait.
2. We will determine if the pedigree below can be for a trait that is autosomal dominant.
Use "A" and "a" as you did for the pedigrees above.
a) Write the genotype of each individual next to the symbol.
b) Is it possible that this pedigree is for an autosomal dominant trait?
c) In conclusion, can two individuals that have an autosomal dominant trait have
unaffected children? (Circle the correct answer below.)
--If two individuals have a dominant trait, none of their ofspring will have the trait.
--If two individuals have a dominant trait, their offspring might or might not have the
trait.
--If two individuals have a dominant trait, their offspring will have the trait.
Autosomal Recessive
3. We will determine if the pedigree below can be for a trait that is autosomal recessive.
Use the following designations:
A = normal
a = the trait (a genetic disease or abnormality)
a) Assuming that the trait is recessive, write the genotype of each individual next to the
symbol.
b) Is it possible that the pedigree above is for an autosomal recessive trait?
c) Assuming that the pedigree below is for a recessive trait, write the genotype next to the
symbol for each person.
d) Is it possible that this pedigree is for an autosomal recessive trait?
e) If a trait is autosomal recessive, what can you conclude about the children if both
parents are affected? (Circle the correct answer below.)
--If both parents are affected, none of the children will be affected.
--If both parents are affected, the children might or might not be affected.
--If both parents are affected, all of the children will be affected.
4. We will determine if the pedigree below can be for a trait that is autosomal recessive.
Use "A" and "a" as you did for the previous example.
a) Write the genotype of each individual next to the symbol.
b) Is it possible that this pedigree is for an autosomal recessive trait?
c) If a trait is autosomal recessive, what can you conclude about the children of two
parents that are not affected? (Circle the correct answer below.)
--If two parents have a dominant trait, the children will not have the trait.
--If two parents have a dominant trait, the children might or might not have the trait.
--If two parents have a dominant trait, the children will have the trait.
5. We will determine if the pedigree below can be for a trait that is autosomal recessive.
a) Write the genotype of each individual next to the symbol.
b) Is it possible that this pedigree is for an autosomal recessive trait?
c) In this pedigree, two generations have been skipped. What can you conclude about
recessive traits skipping generations (is it possible or not)? (Circle the correct answer
below.)
--Recessive traits cannot skip generations.
--Recessive traits can skip generations.
X-Linked Recessive
The conclusions that you made for autosomal recessive traits apply to X-linked traits. In
this exercise, we will work on some additional conclusions because males have only one
X chromosome and females have two.
6 and 7. We will determine if the pedigrees below can be for a trait that is X-linked
recessive. Use the following designations:
XA = normal
Xa = the trait (a genetic disease or abnormality)
Y = Y chromosome (males only)
a) Write the genotype of each individual next to the symbol.
b) Is it possible that the pedigree above is for an X-linked recessive trait?
c) Write the genotype next to the symbol for each person in the pedigree below.
d) Is it possible that this pedigree is for an X-linked recessive trait?
e) Write the genotype next to the symbol for each person in the pedigree below.
f) Is it possible that this pedigree is for an X-linked recessive trait?
g) Write the genotype next to the symbol for each person in the pedigree below.
h) Is it possible that this pedigree is for an X-linked recessive trait?
i) What can you conclude about the children of mothers affected with an X-linked
recessive trait? (Circle the correct answer below.)
--If the mother has an X-linked recessive trait, the children will not have the trait.
--If the mother has an X-linked recessive trait, the children might or might not have the
trait.
--If the mother has an X-linked recessive trait, all of the children will have the trait.
--If the mother has an X-linked recessive trait, females will have the trait but males will
only have the trait if their father also has the trait.
--If the mother has an X-linked recessive trait, males will have the trait, but females will
only have the trait if their father also has the trait.
j) What can you conclude about the father of an affected female? (Circle the correct
answer below.)
--The father of an affected female will not be affected.
--The father of an affected female might or might not be affected.
--The father of an affected female will be affected.
8. We will determine if the pedigree below can be for a trait that is X-linked recessive.
We will continue to use the designations "XA and Xa".
a) Write the genotype of each individual next to the symbol.
b) Is it possible that this pedigree is for an X-linked recessive trait?
c) Which parent did the son get the Xa gene from? In general, you cannot use a pedigree
to tell if father-to-son transmission occurred because the son might have received the
gene from his mother.
d) What can you conclude about father-to-son transmission of X-linked traits? (Circle the
correct answer below.)
--Father-to-son transmission can occur.
--Father-to-son transmission cannot occur.
9. We will determine if the pedigree below can be for a trait that is X-linked recessive.
a) Write the genotype of each individual next to the symbol.
b) Is it possible that this pedigree is for an X-linked recessive trait?
c) What can you conclude about the children if both parents are affected with an X-linked
recessive trait? (Circle the correct answer below.)
--If both parents are affected, none of the children will be affected.
--If both parents are affected, the children might or might not be affected.
--If both parents are affected, all of the children will be affected.
d) How does this conclusion compare with the one you made earlier (question 3e) about
both parents being affected by an autosomal recessive trait?
e) Do the conclusions that you made for autosomal recessive traits apply to X-linked
recessive traits?
10a. If a genetic disease is X-linked recessive, what is the phenotype of a female that has
only one disease allele (Xa)?
b. What is the phenotype of a male with one disease allele?
c. What can you conclude about the number of males that would have the disease
compared to the number of females? (Circle the correct answer below.)
--More males than females are affected.
--Males and females are affected equally.
--More females than males are affected.
Application of Pedigree Analysis
The conclusions about inheritance (above) can be used to help analyze pedigrees. For
each pedigree below, tell if it is possible that the trait can be autosomal dominant,
autosomal recessive, and X-linked recessive. If the pedigree cannot fit a mode of
inheritance, tell why.
Pedigree A
Pedigree B
Questions 10 through 15- Answer with either "yes" or "no." If you answer no, explain
why.
11) Can pedigree A be autosomal dominant? To answer this question, go back and look at
your conclusion for autosomal dominant traits (question 1e).
12) Can pedigree B be autosomal dominant?
13) Can pedigree A be autosomal recessive? To answer this question go back and look at
your conclusion for autosomal recessive traits (question 3e).
14) Can pedigree B be autosomal recessive?
15) Can pedigree A be X-linked recessive? To answer this question, go back and look at
your conclusion for X-linked recessive traits (questions 6i and 6j).
16) Can pedigree B be X-linked recessive?
You must enable JavaScript to give us feedback. Here's how.
Abstract
Some characteristics, like the shape of your hairline, whether your earlobes are attached or detached, and whether
or not you have freckles, are inherited from your parents. In this science project you'll see how writing these
characteristics onto a family tree can help you determine how they are inherited.
Objective
The goal of this science project is to use pedigree analysis to determine how several human physical traits are
inherited.
Introduction
Do you have the same hair color or eye color as your mother? Do people say you look just like your grandfather
when he was your age? When we look at members of a family it is easy to see that some physical characteristics or
traits are shared, but what are the rules that govern the inheritance of these traits?
It was Gregor Mendel, an Augustinian monk and scientist, who first discovered in the 1860's that some traits are
passed down from generation to generation, in very clear and predictable patterns. Today we know that offspring
inherit half of their DNA from each parent. This results in two copies of every gene. Many genes come in several
different versions, called alleles. Alleles are changes in the actual DNA sequence of the gene. When you have two
identical alleles you're said to be homozygous for that gene. People with two different alleles are heterozygous f
that gene. The actual trait, such as red, black, or blond hair, which results from a combination of alleles, is referred
to as the phenotype.
Mendelian traits—the kind of characteristics Mendel first studied—are due to a single gene. Some of such a gene'
alleles are dominant, meaning that if you have even one copy of that allele, you'll display that trait. Mendel took p
plants, which bred true, meaning for generation after generation they had the same phenotypes. (Today we know
that they bred true because they were homozygous for the traits Mendel was looking at). He took a true-breeding
purple flowered plant and crossed it to a true-breeding white flowered plant and saw that the offspring all had purp
flowers. The purple allele was dominant—a single copy of that allele was sufficient. He then took these offspring an
crossed them to one another. He found that their offspring occasionally had white flowers. That's because the white
allele was recessive, which means you need two copies of that allele to display a certain trait. The offspring that
inherited the white allele from both parents displayed the white phenotype.
Figure 1. Two heterozygous parents displaying the dominant phenotype can give rise to offspring with either
the dominant or the recessive phenotype depending on which alleles the offspring inherit.
Just like Mendel observed generations of related pea plants to determine the mode of inheritance for flower color
and other physical traits, scientists can examine generations within a family and discover the mode of inheritance f
human traits. To do this, scientists create family trees, called pedigrees, showing as many generations of a family
as they can and marking who had which phenotype. In order for scientists to understand each other's pedigrees,
they use a standard set of symbols and notations. For example, males are always designated by a square and
females are always designated by a circle.
Figure 2. Here are two pedigrees showing the same three generations of a family. The pedigree on the left is an example of a
dominant trait in this family. The pedigree on the right depicts a recessive trait.
In this science project, you'll create pedigrees for four human physical traits to determine which phenotypes are
dominant and which are recessive. All four are Mendelian traits:
•
Do you have freckles or not?
•
When you interlace your fingers, which thumb is on top—the right or the left?
•
Do you have attached earlobes or detached earlobes?
Figure 3. This diagram shows the difference between detached earlobes and attached earlobes.
•
Some people's hairlines come to a V-shaped point above their forehead. This is called a widow's peak. Do
you have one or not?
Figure 4. Here is an example of a straight hairline versus one with a widow's peak.
•
Terms, Concepts, and Questions to Start Background Research
•
DNA
•
Gene
•
Allele
•
Homozygous
•
Heterozygous
•
Phenotype
•
Mendelian trait
•
Dominant
•
Recessive
•
Mode of inheritance
•
Pedigree
•
Attached earlobe
•
Detached earlobe
•
Widow's peak
•
Genotype
Questions
•
What is a Mendelian trait?
•
What are the different modes of inheritance for a Mendelian trait?
•
How do you draw a pedigree?
Bibliography
•
For a fun and interactive way to learn about dominant and recessive traits try:
EDC Inc. (2002). Weblab: Mendel's Peas. Education Development Center, Inc., and MathResources, Inc.
Retrieved February 19, 2008 from http://www2.edc.org/weblabs/Mendel/MendelMenu.html
Here are some resources for learning how to create pedigrees:
•
Bennett, R.L et al. (1995). Recommendations for standardized human pedigree nomenclature. American
Journal of Human Genetics. 56(3), 745-752. Can be found at:
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1801187
•
Staff. (n.d.). Engle Laboratory, Children's Hospital Boston. How to draw your pedigree. Retrieved February
20, 2008 from
http://www.childrenshospital.org/cfapps/research/data_admin/Site339/mainpageS339P2sublevel9Flevel11
ml
Materials and Equipment
•
Paper
•
Pen
•
Access to a photocopier (optional)
Experimental Procedure
Before starting this science project, you should go through your reference material and familiarize yourself with the
proper way to draw a human pedigree.
1. To start this project, you should draw a pedigree showing the different members of your family.
You must enable JavaScript to give us feedback. Here's how.
Abstract
Some characteristics, like the shape of your hairline, whether your earlobes are attached or detached, and whether
or not you have freckles, are inherited from your parents. In this science project you'll see how writing these
characteristics onto a family tree can help you determine how they are inherited.
Objective
The goal of this science project is to use pedigree analysis to determine how several human physical traits are
inherited.
Introduction
Do you have the same hair color or eye color as your mother? Do people say you look just like your grandfather
when he was your age? When we look at members of a family it is easy to see that some physical characteristics or
traits are shared, but what are the rules that govern the inheritance of these traits?
It was Gregor Mendel, an Augustinian monk and scientist, who first discovered in the 1860's that some traits are
passed down from generation to generation, in very clear and predictable patterns. Today we know that offspring
inherit half of their DNA from each parent. This results in two copies of every gene. Many genes come in several
different versions, called alleles. Alleles are changes in the actual DNA sequence of the gene. When you have two
identical alleles you're said to be homozygous for that gene. People with two different alleles are heterozygous f
that gene. The actual trait, such as red, black, or blond hair, which results from a combination of alleles, is referred
to as the phenotype.
Mendelian traits—the kind of characteristics Mendel first studied—are due to a single gene. Some of such a gene'
alleles are dominant, meaning that if you have even one copy of that allele, you'll display that trait. Mendel took p
plants, which bred true, meaning for generation after generation they had the same phenotypes. (Today we know
that they bred true because they were homozygous for the traits Mendel was looking at). He took a true-breeding
purple flowered plant and crossed it to a true-breeding white flowered plant and saw that the offspring all had purp
flowers. The purple allele was dominant—a single copy of that allele was sufficient. He then took these offspring an
crossed them to one another. He found that their offspring occasionally had white flowers. That's because the white
allele was recessive, which means you need two copies of that allele to display a certain trait. The offspring that
inherited the white allele from both parents displayed the white phenotype.
Figure 1. Two heterozygous parents displaying the dominant phenotype can give rise to offspring with either
the dominant or the recessive phenotype depending on which alleles the offspring inherit.
Just like Mendel observed generations of related pea plants to determine the mode of inheritance for flower color
and other physical traits, scientists can examine generations within a family and discover the mode of inheritance f
human traits. To do this, scientists create family trees, called pedigrees, showing as many generations of a family
as they can and marking who had which phenotype. In order for scientists to understand each other's pedigrees,
they use a standard set of symbols and notations. For example, males are always designated by a square and
females are always designated by a circle.
Figure 2. Here are two pedigrees showing the same three generations of a family. The pedigree on the left is an example of a
dominant trait in this family. The pedigree on the right depicts a recessive trait.
In this science project, you'll create pedigrees for four human physical traits to determine which phenotypes are
dominant and which are recessive. All four are Mendelian traits:
•
Do you have freckles or not?
•
When you interlace your fingers, which thumb is on top—the right or the left?
•
Do you have attached earlobes or detached earlobes?
Figure 3. This diagram shows the difference between detached earlobes and attached earlobes.
•
Some people's hairlines come to a V-shaped point above their forehead. This is called a widow's peak. Do
you have one or not?
Figure 4. Here is an example of a straight hairline versus one with a widow's peak.
•
Terms, Concepts, and Questions to Start Background Research
•
DNA
•
Gene
•
Allele
•
Homozygous
•
Heterozygous
•
Phenotype
•
Mendelian trait
•
Dominant
•
Recessive
•
Mode of inheritance
•
Pedigree
•
Attached earlobe
•
Detached earlobe
•
Widow's peak
•
Genotype
Questions
•
What is a Mendelian trait?
•
What are the different modes of inheritance for a Mendelian trait?
•
How do you draw a pedigree?
Bibliography
•
For a fun and interactive way to learn about dominant and recessive traits try:
EDC Inc. (2002). Weblab: Mendel's Peas. Education Development Center, Inc., and MathResources, Inc.
Retrieved February 19, 2008 from http://www2.edc.org/weblabs/Mendel/MendelMenu.html
Here are some resources for learning how to create pedigrees:
•
Bennett, R.L et al. (1995). Recommendations for standardized human pedigree nomenclature. American
Journal of Human Genetics. 56(3), 745-752. Can be found at:
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1801187
•
Staff. (n.d.). Engle Laboratory, Children's Hospital Boston. How to draw your pedigree. Retrieved February
20, 2008 from
http://www.childrenshospital.org/cfapps/research/data_admin/Site339/mainpageS339P2sublevel9Flevel11
ml
Materials and Equipment
•
Paper
•
Pen
•
Access to a photocopier (optional)
Experimental Procedure
Before starting this science project, you should go through your reference material and familiarize yourself with the
proper way to draw a human pedigree.
1. To start this project, you should draw a pedigree showing the different members of your family.
v