Name: _______________________________________
Core: _____
PEDIGREE CHART – December 3, 2015
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.
 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
Reading a Pedigree Chart
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Generations are identified by Roman numerals and are on different levels.
Males are represented by the square
Females are represented by the circle
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 clear.
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 is carried on the X chromosome.
Autosomal traits are carried on non-sex chromosomes.
Autosomal Recessive
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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.
Autosomal Dominant
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Trait is carried on a non-sex chromosome.
Trait is common in the pedigree.
Trait is found in every generation
Affected individuals transmit the trait to about ½
their children, regardless of sex.
X-linked Recessive
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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.
X-linked Dominant
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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.
Practice Pedigrees:
#1) Answer: _____________________________
#3) ___________________________________
#2) ______________________________