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Genetics
Name_____________________
Date________per____
Pedigrees
Practice Pedigree Analysis
Geneticists illustrate the inheritance of a gene within a family by using a pedigree chart. In a pedigree chart, males
are symbolized by a square (□) and females are symbolized by a circle (○). People who are affected by a condition or
disease are symbolized by a dark square or circle.
This pedigree chart shows the inheritance of albinism in three generations of a family. 1 and 2 represent a couple
who had five children, including a son who is labeled 3 and a daughter who is labeled 5. Only one of their children, 5,
was an albino. One of their sons (3) and his wife (4) had four children, including a son (6) who was an albino.
1
3
2
4
5
7
6
1. Write the genotypes of each individual who is labeled with a number in the pedigree. Use A to represent the
dominant allele and a to represent the recessive allele. Begin by writing in the genotypes of 5 and 6. How do you
know their genotypes?
2. Explain how you can determine the genotypes of 1 and 2. Show the Punnett Square for these parents, and write
their genotypes in the pedigree.
3. Write the genotypes of 3 and 4 in the pedigree.
4. Explain how you can figure out the genotype of 7 and write her genotype in the pedigree.
= Female
= Male
= Affected Female
= Affected Male
b) Is it possible that the pedigree above is for an autosomal 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 child that has a
dominant characteristic?
2. We will determine if the pedigree below can be for a trait that is autosomal dominant..
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?
Autosomal Recessive
3. We will determine if the pedigree below can be for a trait that is autosomal recessive.
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?
4. 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) If a trait is autosomal recessive, what can you conclude about the children of two parents
that are not affected?
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 no individuals with the disease. What can you
conclude about recessive traits “skipping” generations? Do the alleles skip generations?
X-Linked Recessive
Use the following symbols for X-linked alleles:
XA = normal
Xa = the trait (a genetic disease or abnormality)
Y = Y chromosome (males only)
6. We will determine if the pedigrees 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 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
characteristic?
7. 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?
d) What can you conclude about father-to-son transmission of X-linked traits?
8. 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?
d) How does this conclusion compare with the one you made earlier if about both parents
being affected by an autosomal recessive trait?
e. What can you conclude about the number of males that would have the disease
compared to the number of females?
Practice
The conclusions about inheritance (above) can be used to help analyze pedigrees.
Pedigree A
10. Can the trait shown in pedigree A be autosomal dominant?
Explain why by referring to specific individuals.
11. Can the trait shown in pedigree A be autosomal recessive?
Explain why by referring to specific individuals.
12. Can the trait shown in pedigree A be X linked recessive?
Explain why by referring to specific individuals.
Pedigree B
13. Can the trait shown in pedigree B be autosomal dominant?
Explain why by referring to specific individuals.
14. Can the trait shown in pedigree B be autosomal recessive?
Explain why by referring to specific individuals.
15. Can the trait shown in pedigree B be X linked recessive?
Explain why by referring to specific individuals.
Questions to Promote Thinking
We have used two types of models of inheritance: a Punnett Square and a pedigree. Each has advantages and
disadvantages.
6. What are some advantages of a Punnett Square as a model of inheritance?
What is one limitation of a Punnett Square as a model of inheritance?
What is one advantage of a pedigree as a model of inheritance?
What is one limitation of a pedigree as a model of inheritance?