Download Pedigrees - Humble ISD

Pedigree Charts
The family tree of genetics
What is a pedigree?
Constructing a pedigree
Interpreting a pedigree
Some History
 Hemophilia has played
an important role in
Europe's history
 The disease began to
crop up in Great Britain's
Queen Victoria’s children
 It became known as the
"Royal disease" because
it spread to the royal
families of Europe
through Victoria's
descendants
How it Spread
 it spread through the
Royal Houses of
Europe as monarchs
arranged marriages to
consolidate political
alliances.
 We can trace the
appearance of
hemophilia as it
popped up in Spain,
Russia, and Prussia
by looking at the
family tree.
The Royal Family Tree
What is a Pedigree Chart?
 A Pedigree chart traces the inheritance
of a particular trait through several
generations.
 One GOAL of using a pedigree chart is
to figure out who are carriers of the
trait, because this information is typically
unknown.
Steps to Creating a Pedigree
1. A genetic counselor will first gather
information regarding who the family
members are and how are they related. This
will go back a few generations.
2. The genetic counselor will then ask who has
the trait of interest. (Shows the trait)
3. After researching, the genetic counselor uses
all of this information to construct a Pedigree
chart, with all the family members’ names
and genotypes written below each symbol.
Constructing a Pedigree
 Male
 Female
Constructing a Pedigree
 Married Couple– Horizontal Line
 Siblings
– Vertical line
 More than one Sibling:
– a horizontal line is drawn
with a vertical line coming
down for each sibling.
Constructing a Pedigree
Roman numerals to the left of the pedigree
show the generations.
Birth Order: children are listed in birth order
with oldest on left and youngest on the right.
I
II
III
Constructing a Pedigree
 Fraternal twins– Two line branching from the
same point
– two eggs and two sperm cells.
 Identical twins– Also called Maternal Twins
– Identical or Maternal Twins (first
set above) are drawn branching
off of the same point, but are
also connected to each other
More Symbols in a Pedigree Chart
 Full Shaded:
– Affected person who
shows a disorder
 Half shaded:
– Autosomal carrier
 Circle with dot:
– X-linked carrier –always
female
 Deceased
Sex-Linked Traits
 Genes located on the X chromosomes
(some cause diseases)
 The Y is much smaller, contains few genes
 Sex Linked Disorders
– Color Blindness (red-green)
– Hemophilia ("bleeders disease)
– Duchenne Muscular Dystrophy (weakening/loss
of skeletal muscles)
 More common for males to display disorders
Sex-Linked Traits
 Consider hemophilia
How do you find the genotypes of the
persons in the chart?
 Start with the person showing the trait.
 Look at parents of this individual and ask
yourself: what would the parent’s
genotypes have to be (in a Punnett
square) to produce an offspring with this
genotype?
 If there is not enough information to
figure out the entire genotype then a
question mark is used to take the place
of the uncertain allele. Ex. T?
Example Problem
Shaded=deaf
(D) is normal hearing
(d) is deaf
 Is deafness a dominant or
recessive trait?
recessive
 To show deafness, what
genotype does this son have
to have? dd
 For two parents who have
normal hearing to have a deaf
son, they both must be
carrier. What are the parent
genotypes?
Dd
Example Problem
 Write the genotypes for the parents and son
under the correct circle/boxes, half-shading
carriers.
Shaded=deaf
(D) is normal hearing
Dd
Dd
(d) is deaf
dd
Predicting using Pedigree Charts
 Pedigrees are used to find out:
– who are carriers of the disorder &
– the probability of having a future child with
the disorder.
 To begin to interpret a pedigree, first
determine if the disorder is:
– Autosomal dominant
– Autosomal recessive
– Sex-linked (carried on the X chromosome)
Interpreting a Pedigree Chart
First ask:
Is it a Sex-linked or Autosomal Disorder?
– If there is a much larger number of
males than females who are affected
then the disorder is Sex-linked.
– If there is a 50/50 ratio between males
and females who are affected then the
disorder is autosomal.
Interpreting a Pedigree Chart
If it is autosomal disorder then ask:
Is it dominant or recessive?
– If two parents do not show the trait
and their children do show it, then it is
an autosomal recessive disorder
 (parents are heterozygous)
– If the disorder is autosomal
dominant, then at least one of the
parents must show the disorder.
Note:
 The following pedigree charts show infected
individuals only.
 Carriers are unknown at this point.
Practice Examples
Does this pedigree show a
Sex-linked or Autosomal disorder?
Answer:
Sex-Linked Disorder
much larger number of males are affected
Practice Examples
Does this pedigree show a
Sex-linked or Autosomal disorder?
Answer:
Autosomal Disorder
50/50 ratio between males and females
Practice Examples
Does this pedigree show a Autosomal
Dominant or Recessive disorder?
Answer:
Autosomal Dominant Disorder
At least one parent of the affected
children show the disorder
Practice Examples
Does this pedigree show a
Sex-linked or Autosomal disorder?
Answer:
Autosomal Disorder
50/50 ratio between males and females
Practice Examples
Does this pedigree show a Autosomal
Dominant or Recessive disorder?
Answer:
Autosomal Recessive Disorder
Two parents do not show the trait and their
children do show it (heterozygous parents)
Autosomal Recessive
Genotypes and Carrier determination
D = Normal hearing
Dd
dd
Dd
dd
Dd
dd
Dd
d = deafness
Dd
dd
dd
Dd
dd
D?