Transcript Pedigree Charts

Pedigree Charts
What is a Pedigree?
• Pedigree
– chart of the genetic history of a family over
several generations.
• Since you cannot make humans of different
types breed together a pedigree chart offers
an ethical way of studying human genetics.
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
Constructing a Pedigree
• Female
• Male
Symbols used in pedigree
charts
•
•
•
•
•
A marriage with five children, two
daughters and three sons. The middle
son is affected by the condition.
Normal male
Affected male
Normal female
Affected female
Marriage (mating)
Eldest child  Youngest child
Connecting Pedigree Symbols
Examples of connected symbols:
• Fraternal twins
• Identical twins
Symbols in a Pedigree Chart
• Affected
• Deceased
Organizing the pedigree chart
– Generations are identified by Roman
numerals
I
II
III
IV
Organizing the pedigree chart
• Individuals in each generation are identified by Roman
numerals numbered from the left
• Therefore the affected individuals are II3, IV2 and IV3
I
II
III
IV
Interpreting a Pedigree Chart
1. Determine if the pedigree chart shows an
autosomal or (sex) X-linked disease.
– If most of the males in the pedigree are
affected by the disorder, then it is (sex)
X-linked
– If it is a 50/50 ratio between men and
women the disorder is autosomal.
Example of Pedigree Charts
• Is it Autosomal or X-linked?
Answer
• Autosomal
Interpreting a Pedigree Chart
2. Determine whether the disorder is
dominant or recessive.
– If the disorder is dominant, one of the
parents must have the disorder.
– If the disorder is recessive, neither
parent has to have the disorder because
they can be heterozygous.
Example of Pedigree Charts
• Dominant or Recessive?
Answer
• Dominant
Example of Pedigree Charts
• Dominant or Recessive?
Answer
• Recessive