Download Pedigree notes and practice

Name: ______________________________________Date: _____Period: _____ Alpha #: _____
Pedigrees
Because humans reproduce so infrequently and have such a long lifetime, it is more difficult to
study genetic disorders in humans. Instead of experimental biology (as in breeding pea plants),
genetics is studied in humans through pedigree analysis. Pedigrees are family trees which show the
phenotypic or genotypic inheritance patterns using standard genetics symbols. A phenotypic pedigree
shows just the affected individuals and a genotypic pedigree adds in the carriers as well. Sometimes a
pedigree is a combination of both phenotypic and genotypic depending on the available information.
Pedigrees are useful tools in assessing inheritance of genetic disorders. The can be used in infer the
mode of inheritance and thus the probability of a child being affected by the trait.
8 simple rules for constructing a pedigree:
1. Males are squares
2. Females are circles
3. Horizontal lines indicate marriage
4. Vertical lines indicate children
5. For both phenotypic and genotypic pedigrees:
a. Color in circle or square if person shows the trait
b. Do not color in circle or square if person does not show the trait
6. For genotypic pedigrees only:
a. Color in the right half of the circle or square if the person is a carrier
b. The genotype may be written below the individual
7. Generations are numbered from the oldest to youngest using roman numerals
8. Individuals in each generation are numbered left to right and are in birth order from left to
right in their family
Pedigree Patterns: Autosomal recessive, autosomal dominant, and X-linked recessive traits all have
distinct patterns in pedigrees.
A: Autosomal recessive:
o affects males and females equally
o Children with trait have do not need a parent with
the trait
o both male and female carriers possible
B: Autosomal dominant:
o affects males and females equally
o Children with trait have must have one parent with the
trait
o No carriers
C: X-linked recessive:
 Affects many more males than females
 Children with trait have do not need a parent with the
trait
 No male carriers
Practice pedigrees:
1. Is left-handedness autosomal dominant, autosomal recessive or sex-linked recessive trait?
A family has four children: two boys and then two girls. The parents are both right-handed. The first son is
left-handed while the other son is right-handed as are both daughters. The fourth daughter then marries a
man with a left-handed mother. Their children are a left-handed boy and two right-handed girls.
a.
b.
c.
d.
e.
f.
Draw a pedigree below for this family. Label each generation and each person.
Color in the circles and squares. Remember to only color in those affected by the trait.
How is left-handedness most likely inherited?
Can you identify any carriers for left-handedness?
What was the chance of individual II – 2 being heterozygous ?
What was the chance of individual III – 1 being left-handed?
2. Is male pattern baldness an autosomal dominant, autosomal recessive or sex-linked recessive trait?
A family has four children: two boys and then two girls. The parents are both normal but the father has no
history of baldness in his family. Their second boy became bald at age 30. The second daughter marries a
man who was already balding at age 25. She and her husband have two girls and then a boy who goes bald
at age 28.
a.
b.
c.
d.
e.
f.
Draw a pedigree below for this family. Label each generation and each person.
Color in the circles and squares. Remember to only color in those affected by the trait.
How is baldness most likely inherited?
Can you identify any carriers for baldness?
What are the chances of individual II-3 being a carrier?
If individual III-3 marries a normal woman with no history of baldness in her family, what are the
chances of bald sons? Of carrier daughters?
3. Is the ability to roll the tongue an autosomal dominant, autosomal recessive or sex-linked recessive
trait?
A man with the ability to roll his tongue married a woman with no history of tongue rolling in her
family and had two boys then a girl. The boys could roll their tongues but the girl could not. The
first boy married a woman who could roll her tongue and their two girls could too.
a.
b.
c.
d.
e.
Draw a pedigree below for this family. Label each generation and each person.
Color in the circles and squares. Remember to only color in those affected by the trait.
How is tongue rolling most likely inherited?
Is it possible to have a carrier for tongue rolling?
Is individual II – 4 heterozygous or homozygous?
Pedigrees:
1. Type of inheritance
_______________________
Reasoning:
2. Type of inheritance
_______________________
Reasoning:
3. Type of inheritance
_______________________
Reasoning:
4. Type of inheritance
_______________________
Reasoning:
Name: _______________________________ Date: _____ Period: _____ Alpha #: _____
1. What type of inheritance pattern does the above pedigree illustrate?
Incomplete dominance
Autosomal recessive
Sex-linked
Autosomal dominant
2. For the traits being followed in this pedigree, individuals II-1 and II-4 can be
classified as:
Homozygous recessive
Homozygous dominant
Mutants
Carriers
3. If individual III-2 marries a person with the same genotype as individual I-1,
what is the chance that one of their children will be affected with hemophilia?
0%
50%
25%
75%
1. What is the most likely inheritance pattern for the pedigree?
Autosomal dominant
Sex-linked
Autosomal recessive
Multiple alleles
2. Using the pedigree, what do you know about individual’s III-1’s mother?
She has the trait
She is a carrier
She is homozygous recessive
She is homozygous dominant
3. According to the pedigree how many of the children in the III generation show
the normal trait?
1
4
2
5