Name________________________________ Date______________
Biology 513
Pedigrees – Guided Lesson
Genotypes and Symbols
1) Identifying symbols:
Symbol
Phenotype
Female without trait
Female with trait
Male without trait
Male with trait
2) What are the genotypes for recessive and dominant traits? (Use A and a)
a. Recessive trait __________________________________________________________
b. Dominant trait __________________________________________________________
Recessive and Dominant Traits
3) What genotypes are shaded if the trait is a recessive trait? Shade appropriate circles and squares
below:
Genotype
Symbols
aa
AA
Aa
4) What genotypes are shaded if the trait is a dominant trait? Shade appropriate circles and squares
below:
Genotype
Symbols
aa
AA
Aa
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5) If the trait is an autosomal recessive trait (gene not linked to an X or Y chromosome), identify
the genotypes of ALL individuals in the pedigree below. Write the genotype beneath each circle
and square. Use “A” and “a” as your alleles:
I
II
III
6) What pattern do you notice about a pedigree showing a recessive trait? Circle this pattern in the
pedigree above as many times as it appears.
7) If the trait is an autosomal dominant trait (gene not linked to an X or Y chromosome), identify
the genotypes of ALL individuals in the pedigree below. Write the genotype beneath each circle
and square. Use “A” and “a” as your alleles:
I
II
III
IV
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8) What pattern is observed in a pedigree showing a dominant trait?
9) Review recessive versus dominant traits: How do you know if a trait is recessive or dominant
from a pedigree?
X-linked Recessive Traits (Examples: Hemophilia and Colorblindness)
10) If the trait is X-linked recessive, then the X and Y chromosomes need to be indicated in the
genotype. In the table below, identify the phenotypes of ALL the possible genotypes below
AND assign the appropriate pedigree symbol. The phenotype should include the gender
followed by whether the individual will have the dominant or recessive trait:
Genotype
Phenotype
Symbol
XAXA
XAXa
XaXa
XAY
XaY
11) If the trait is X-linked recessive, how many alleles does a male need to inherit to show the
recessive trait?
12) If the trait is X-linked recessive, how many alleles does a female need to inherit to show the
recessive trait?
13) Which gender is more likely to show an X-linked recessive trait? Why?
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14) (a) In an X-linked recessive trait, which gender is more likely to show the trait and thus be
shaded more often in the pedigree? (b) What would this individual’s symbol look like? Draw it.
(c) How often would you see this symbol appear in a pedigree compared to other symbols?
15) Males who have an X-linked recessive trait inherited the recessive allele from which parent?
Mom or dad? Explain your answer.
16) If the trait is an X-linked recessive trait, identify the genotypes of ALL individuals in the
pedigree below. Write the genotype beneath each circle and square. Make sure you write X and
Y chromosomes and use “A” and “a” as your alleles:
I
II
III
17) If you determined that the trait is recessive, how do you distinguish whether it is autosomal
recessive or X-linked recessive in a pedigree? Compare the X-linked recessive pedigree in
question 16 above with the autosomal recessive pedigree in question 5.
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X-linked Dominant Traits
18) If the trait is X-linked dominant, identify the phenotypes of all the possible genotypes below
AND assign the appropriate pedigree symbol.
Genotype
Phenotype
Symbol
XAXA
XAXa
XaXa
XAY
XaY
19) If a male has an X-linked dominant trait, what percentage of his daughters would show the Xlinked dominant trait? Explain.
20) If the trait is an X-linked dominant trait, identify the genotypes of ALL individuals in the
pedigree below. Write the genotype beneath each circle and square. Make sure you write X and
Y chromosomes and use “A” and “a” as your alleles:
I
II
III
IV
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21) If you determined that the trait is dominant, how do you distinguish whether it is autosomal
dominant or X-linked dominant from a pedigree? Compare the X-linked dominant pedigree in
question 20 above with the autosomal dominant pedigree in question 7.
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