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PEDIGREE CHARTS
A family history of a genetic condition or trait
WHAT IS A PEDIGREE CHART?
 Pedigree
charts show a record of the family of
an individual.
 They can be used to study a hereditary
condition or trait.
 They are especially useful when there are
large families that cover several generations.
© 2007 Paul Billiet ODWS
STUDYING HUMAN GENETICS
Today
genetic engineering has new
tools to offer doctors studying genetic
diseases
A genetic counselor will still use
pedigree charts to help determine the
distribution of a disease in an affected
family
© 2007 Paul Billiet ODWS
READING A PEDIGREE CHART
 Generations are identified by Roman numerals
& are on different levels.
I
II
III
IV
 Males are represented by the square

Females are represented by the circle
I
II
III
IV
 Parents are connected with a horizontal line.
 Offspring are below the parents and the bracket
is connected by a vertical line.
 Siblings are within the same bracket.
Affected individuals (those that show the trait) are
shaded.
 Unaffected individuals (those that do not show the
trait) are blank.

READING THE SYMBOLS USED IN PEDIGREE CHARTS

Normal male

Affected male

Normal female

Affected female
A marriage with five children, two
daughters and three sons. The eldest
son is affected by the condition.


Marriage
Eldest child  Youngest child
Genetic Counselors use a pedigree chart to predict the
probability of transmitting an inherited disorder.
Sex-linked traits are carried on sex chromosomes
(X or Y).
Example:
Colorblindness
which is carried
on the X
chromosome.
Autosomal traits are carried on non-sex
chromosomes.
Autosomal recessive
Trait is carried on a non-sex
chromosome.
Trait is rare in pedigree.
Trait often “skips”
generations (hidden in
heterozygous carriers).
Affects males and females
equally.
Example: Cystic fibrosis
Autosomal dominant
Trait is carried on a non-sex chromosome.
Trait is common in the pedigree.
Trait is found in every generation
Example: Huntington’s
Disease
Affected individuals transmit the trait to about ½ their
children, regardless of sex.
X-linked recessive
Trait is carried X chromosome.
Trait is rare in pedigrees and “skips” generations.
Affected fathers DO NOT pass trait to their sons.
Males are affected more often than females.
Example: Colorblindness;
Hemophilia
X-linked recessive disorder: Hemophilia in European royalty
X-linked dominant
Trait is carried X chromosome.
Trait is common in pedigrees.
Affected fathers pass trait to ALL of their daughters.
Males and females are equally affected.
Extremely
unusual; often
lethal in males
(before birth)
and only seen in
females.
#1) Let’s try to figure out some together!
Is this trait autosomal or sex-linked?
Is this trait dominant or recessive?
Answer: autosomal dominant  Each affected individual has an
affected parent; no skipping generations; normal siblings of affected
individuals have all normal children; males and females are affected
equally; about ½ the offspring of an affected individual are affected.
#2) Let’s try to figure out some together!
Is this trait autosomal or sex-linked?
Is this trait dominant or recessive?
Answer: X-linked recessive  Affected males do not pass trait to any
of their sons; skips a generation; female carriers can produce sons
with trait; more likely to affect males than females.
#3) Let’s try to figure out some together!
Is this trait autosomal or sex-linked?
Is this trait dominant or recessive?
Answer: autosomal recessive
 affects males and females
equally; rare in pedigree; often
skips generations.