Download Pedigrees

Pedigree Charts
The family tree of genetics
Overview
I.
What is a pedigree?
a.
b.
II.
Definition
Uses
Constructing a pedigree
a.
III.
IV.
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.
 Scientists or a genetic counselor would find
out about your family history and make this
chart to analyze.
Constructing a Pedigree
 Female
 Male
Connecting Pedigree Symbols
Examples of connected symbols:
 Fraternal twins
 Identical twins
Connecting Pedigree Symbols
Examples of connected symbols:
 Married Couple
 Siblings
Example
 What does a pedigree chart look like?
Symbols in a Pedigree Chart
 Affected
 X-linked
 Autosomal carrier
 Deceased
Interpreting a Pedigree Chart
1. Determine if the pedigree chart shows an
autosomal or X-linked disease.
– If most of the males in the pedigree are
affected the disorder is 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
1. 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
Historic Pedigrees
 Queen Victoria- Hemophilia sex linked blood
disorder( bleeder)
 Hemophilia is a hereditary (X-linked, recessive)
blood disorder that affects the proper clotting of
blood. It is a disease that affects males much more
frequently (1 in 10,000) than females (1 in
100,000,000). This occurs because a critical bloodclotting gene is carried on the X chromosome. So
because males carry only one X chromosome, if it is
defective he will have hemophilia. Females, on the
other hand, carry two X chromosomes. If only one is
defective, the other normal X chromosome can
compensate. The woman will have normal blood
clotting, but she will still be a carrier of the recessive
defective gene. A woman will know if she is a carrier
sooner through genetic testing or later if any of her
children are hemophiliacs. Naturally, female
hemophiliacs are rare because it takes two
defective X chromosomes in order for the condition
to occur. Women with the recessive gene that codes
for hemophilia simply pass it on to their offspring.
Royal Disease
 Hemophilia has often been referred to as The
Royal Disease. The marriage of England's Queen
Victoria and Prince Albert marked the beginning of
hemophilia in the British royal line. Queen Victoria,
Queen of England from 1837 to 1901, was a
carrier of the hemophilia gene. She had nine
children and as English royal family members
married into royalty of other countries, the disease
eventually infected most of the royal houses of
Europe. So hemophilia gained its title of The Royal
Disease because it spread through the royal
families of Europe through Victoria's descendants.
 Queen Victoria's eighth child, Leopold, was
her only hemophiliac child. Two of Queen
Victoria's daughters, Beatrice and Alice,
were also carriers of hemophilia. The
daughter's were the links that passed the
disease onto the Spanish, German and
Russian royal families.
Summary
 Pedigrees are family trees that explain your
genetic history.
 Pedigrees are used to find out the
probability of a child having a disorder in a
particular family.
 To begin to interpret a pedigree, determine if
the disease or condition is autosomal or Xlinked and dominant or recessive.