Pedigree Analysis
Pedigree
• Shows a family tree with
respect to a given trait.
Pedigree analysis reveals
patterns of inheritance
• Determines the probability
of an affected offspring for
a given cross
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Why do Pedigrees?
• Punnett squares and chi-square tests work well for
organisms that have large numbers of offspring and
controlled matings, but humans are quite different:
(a) Small families. Even large human families have 20 or
fewer children.
(b) Uncontrolled mating. Often with heterozygotes.
(c) Failure to truthfully identify parentage.
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Individuals may wish to be tested if:
• There is a family history of one specific disease
• They show symptoms of genetic disorder
• They are concerned about passing on a genetic
problem to their children.
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Autosomal Dominant
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Autosomal Recessive
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X-linked Dominant
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X-linked Recessive
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Y-linked
• Very rare
• Related to genes unique to the Y-chromosome
• Present only in males
• Only passed from father to son
• Always expressed
• Does not skip generations
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Mitochondrial
• Trait is inherited from
mother only.
• All children of a mother
are at risk to be
affected or carriers.
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Practice 1
• In humans, albinism is a recessive trait. The disorder causes a
lack of pigment in the skin and hair, making an albino appear
very pale with white hair and pale blue eyes. This disorder can
also occur in animals, a common albino found in a laboratory
is the white rat. The pedigrees below trace the inheritance of
the allele that causes albinism.
• Given the following genotypes, describe the phenotypes
(normal or albino)
AA = __________________________
Aa = _________________________
aa = __________________________
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Practice 1
a) How many children
does the couple
have?
b) What is the sex of
the oldest child?
c) How many
grandchildren does
the couple have?
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Practice 2
Two normally-pigmented parents have 3 children. The first
child (a girl) and their second child (a boy) have normal
pigmentation. Their third child (a girl) has albinism. That girl
marries a normally pigmented male and they have four
children. The first three (two girls and a boy) have normal
pigmentation. Their fourth child (a girl) has albinism like her
mother. Construct the pedigree for this case.
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