Pedigree Analysis
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A pedigree is a method scientists use to study the inheritance patterns of humans. It is very
easy to breed certain plants and animals and study their inheritance patterns but we cannot
study inheritance in humans in the same way. Humans have very few children compared to
plants and many animals, humans often have children when they are in their 20s or 30s which
means large gaps between generations and hardest of all, it would be unethical to breed
humans in the same way that we breed cows or pea plants.
Pedigrees help us put together the puzzle of human inheritance and can teach us which
characteristics are dominant and which are recessive. Pedigrees use symbols to show us if
someone is a male or a female and if they are affected by a certain characteristic or not.
Affected
Male
Male
Affected
Female
Female
In the example below, a male with attached earlobes, a recessive trait, would be represented
with a black square while a female with free hanging earlobes, a dominant trait, would be
represented with a white circle.
f
f
F
f
Generation 1
(grandparents
)
Generation
2 (parents)
F
F
F
f
F
f
f
f
F
f
F
f
Generation
F 3 (children)
F
If we didn’t know if attached earlobes were dominant or recessive we could figure it out by
looking at this pedigree. We would see the attached earlobe gene must have been hiding in the
Pedigree Analysis Questions
second generation since two parents without attached earlobes had a child with attached
earlobes. If a gene is hiding then we know that it is recessive.
1. One of these examples shows a recessive inheritance pattern and one of them shows a
dominant inheritance pattern. Which is which?
A
.
B
.
2. Fill in the missing genotypes in this pedigree.
D
d
D
d
A.
D
D
B.
3. The following pedigree shows the inheritance pattern for widows peaks. Based on this
pedigree, are widow’s peaks a dominant or recessive trait? Explain why.
4. Sana and Caleb would like to have a child together. Both are healthy but Caleb’s father
and mother have Huntington’s Disease. Look at the pedigree and decide if there is a risk
that Sana and Caleb’s child could be born with the genes for Huntington’s Disease.
Pedigree Analysis Questions
C
a
l
e
b
S
a
n
a
Answer Sheet
1. In A. Both parents have a dominant diseased gene a recessive healthy gene. In B it is
the opposite, both parents have a dominant healthy gene and are carrying a recessive
diseased gene.
a. Dominant
b. Recessive
2. The disease is dominant so B must have two recessive copies to not be affected. In
order for B to receive two recessive genes each parent must have at least one recessive
gene.
a. Dd
b. dd
3. Widow’s peaks are a dominant trait. The parents in the second generation both have a
widow’s peak but have children that do not have a widow’s peak because they are both
carrying recessive genes for not having a widow’s peak.
4. Based on the pedigree we can determine that Huntington’s Disease is a dominant
disease. Since both of Caleb’s parents have the disease but he doesn’t we can
determine that his parents are carrying a healthy gene that is covered up by the sick
gene. Since both Caleb and Sana are healthy and Huntington’s is a dominant disease,
we can determine that they both are homozygous recessive for not having Huntington’s
Disease.