Transcript Pedigrees

Pedigree Charts
The family tree of genetics
Overview
I.
What is a pedigree?
a.
b.
II.
Constructing a pedigree
a.
b.
III.
Definition
Uses
Symbols
Connecting the symbols
Interpreting a pedigree
What is a Pedigree?
 A pedigree is a chart of the genetic history of family
over several generations for a particular trait.
 Can be used:
– to discover the inheritnace pattern of a disease
or disorder (autosomal versus sex-linked,
dominant vs. recessive)
– Along with punnett squares to determine
genotype and phenotypes probabilities
Constructing a Pedigree Gender symbols
 Female
 Male
Connecting Pedigree Symbols
 Married couple
(or parents of a child)
 Siblings
Connecting Pedigree Symbols
Twins:
 Fraternal twins
(do not have identical DNA)
 Identical twins
(DO have identical DNA)
Example
 Example pedigree chart (blank)
Symbols in a Pedigree Chart
 Affected
 X-linked carrier
 Autosomal carrier
 Deceased
Interpreting a Pedigree Chart
1. Determining if the pedigree chart shows an
autosomal or X-linked disorder/ disease
X-linked disorders occur on the X chromosome
(remember males have only 1 X chromosome)
Autosomal disorders occur on the other
chromosomes (pairs 1-22)
Therefore…
If more of the males in the pedigree
are affected the disorder is Xlinked
If there is not a significant difference
in # of males and females the
disorder is autosomal.
Example of Pedigree Charts
 Example A: Autosomal or X-linked?
Answer
 Autosomal
Interpreting a Pedigree Chart
2. Determining whether the disorder is
dominant or recessive
– If the disorder is dominant, one of the
parents of an affected individual must
have the disorder.
– If the disorder is recessive, neither
parent has to have the disorder because
they can be heterozygous (carriers).
Example B
 Dominant or Recessive?
Answer
 Dominant
Example C
 Dominant or Recessive?
Answer
 Recessive
Summary
 Pedigrees are family trees that illustrate
genetic history.
 To begin to interpret a pedigree, determine if
the inheritance pattern of the
disorder/disease (autosomal or X-linked &
dominant or recessive)
 Pedigrees can be used to find out the
probability of a child having a disorder in a
particular family.