Download Pedigrees

Pedigree Charts
The family tree of genetics
What is a Pedigree?
 A pedigree is a flow chart that uses symbols to
show the genetic history of family over several
generations.
 Genetic counsellor’s ask questions about your
family history and make a pedigree chart to
analyze and provide advice.
SYMBOLS USED IN PEDIGREE CHARTS
•
•
•
•
Male
Matting / Married
Female
Affected
Identical Twins
Offspring
Non-identical
Constructing a Pedigree
Each generation is shown on a different
ROW
Matting Couples are connected and
their children are connected in between
below.
Children are added from left to right
according to birth year.
EXAMPLE:
How many generations?
How many couples?
How many sisters?
How many in each
generation are affected?
EXAMPLE:
How many generations?
3
How many couples?
3
How many sets of
sisters?
1 pair in generation 3
How many in each
generation are affected?
2 in Gen. 2
1 in Gen. 3
Uses of a Pedigree
 A pedigree is a way to analyze how a trait
is inherited through generations
 Pedigrees help uncover the method of
inheritance (ex: x-linked).
 To determine the presence of absence of a
particular trait, but more often the presence
of a disease.
Inheritance Pattern
 AUTOSOMAL INHERITANCE: the disease
is located on a chromosome number 1-22
(not a sex chromosome)


* If there is a 50 / 50 split between males and
females the disease is most likely autosomal
* if more females are affected than males
Dominant or Recessive?
 AUTOSOMAL DOMINANT: Only 1 copy of
the disease is needed for the disease to
appear
 * Appears in every generation
Dominant or Recessive?
 AUTOSOMAL RECESSIVE: 2 copies of
the disease is needed for the disease to
appear

* Can skip a generation
Inheritance Pattern
 X-Linked: the disease is located on the xchromosome

- the trait appears more frequently in males
because males only have 1 X chromosome.
 - if a woman is affected, her dad MUST be
affected
•
EXAMPLE 1: Is it Autosomal or X-linked?
Answer
 Autosomal
 DOMINANT OR RECESSIVE?
Rationale: Because there are 3 females and 3 males affected
Answer
 Autosomal
 DOMINANT - in every generation
Example of Pedigree Charts
 Dominant or Recessive?
Hint: Add genotypes above each individual to determine the answer
Answer
 Dominant
dd
dd
Dd
Dd
dd
dd
dd
Dd
Dd
dd
dd
Dd
Dd
Example of Pedigree Charts
 Dominant or Recessive?
Answer
 Recessive
Dd
Dd
Dd / DD
Dd
Dd
Dd / DD
Dd
dd
dd
Dd
Dd
dd
dd