What is a
Pedigree…
And Nooooo it’s not Dogfood.
Biology I
Searcy Ninth Grade Center
It is a diagram that shows how a trait
is inherited through several generations.
 Pedigree for the Albino Trait
 Pedigree for a Sex Linked Trait
Human geneticists illustrate the inheritance of a
gene within a family by using a pedigree chart.
• Squares = males
• Circles = females
• Shaded = individual has the
•
•
•
•
trait or condition
Unshaded = individual does
not have trait or condition
Horizontal line = marriage
Vertical line = offspring,
arranged from left to right in
order of birth
Roman numerals - label
different generations
= unaffected female
= affected female

= female carrier
= unaffected male
= male affected by one trait
= male carrier
And more...
Patterns of Inheritance
 By analyzing patterns of inheritance,
biologists can learn about genetic
diseases.
 If a trait is autosomal, it will
appear in both sexes equally and if it is sexlinked, it is usually seen only in males.
 The major use of pedigree analysis is in clinical
evaluation and counseling of patients with
inherited abnormalities.
Patterns of Recessive Traits
• May appear to “skip” generations
• Most children of normal and affected parents
are normal
• AA x aa ---> Aa
• All children of two affected parents will be
affected
• aa x aa ---> aa
Patterns of Recessive Traits
• Normal parents may produce affected
offspring
• Aa x Aa ---> 3/4 normal; 1/4 affected
Patterns of Dominant Traits
• Trait tends to appear each generation
• Normal and affected individual expected to
produce normal and affected children
(approximate 1:1 ratio)
• Affected individuals generally heterozygous if
rare trait
• Aa x aa ---> 1/2 Aa; 1/2 aa
Patterns of Dominant Traits
• At least one parent must be affected in order
for children to be affected
• Aa x aa
• Normal parents will always produce normal
offspring
• aa x aa ---> aa