Pedigree Charts
The family tree of genetics
What is a pedigree?
Constructing a pedigree
Interpreting a pedigree
Slide # 2
What is a Pedigree Chart?
1. A Pedigree chart traces the inheritance of a
particular trait through several generations.
2. One GOAL of using a pedigree chart is to
figure out who are carriers of the trait,
because this information is typically unknown.
a. Carrier: someone who is heterozygous
for a trait.
Slide # 3
Constructing a Pedigree
Female
Male
Slide # 4
Constructing a Pedigree
1. Married Couple:
– Horizontal Line
2. Children:
- Vertical line
3. More than one child:
– a horizontal line is drawn
with a vertical line coming
down for each sibling.
Slide # 5
Constructing a Pedigree
1. Fraternal twins- can be the same or
different gender
a. Two line branching from the
same point
b. two different eggs and two
different sperm cells.
2. Identical twins-almost always same
gender
a. Also called maternal twins
b. Same as fraternal twins but a
horizontal line is added.
c. One egg and one sperm unite
and later splits to create two
babies
Generations
Slide # 6
1. Roman numerals to the left of the pedigree
show the generations.
2. Birth Order: children are listed in birth order
with oldest on left and youngest on the right.
I
II
III
Slide # 7
More Symbols in a Pedigree Chart
1. Full Shaded:
a. Affected person who
shows a disorder
2. Half shaded:
– Autosomal carrier
3. Circle with dot:
– X-linked carrier –always
female
4. Deceased
Slide # 8
Predicting using Pedigree Charts
1. Pedigrees are used to find out:
a. who are carriers of the disorder
b. the probability of having a future child with
the disorder.
2. To begin to interpret a pedigree, first determine
if the disorder is:
a. Autosomal dominant
b. Autosomal recessive
c. Sex-linked (carried on the X chromosome)
Slide # 9
Interpreting a Pedigree Chart
First ask:
Is it a Sex-linked or Autosomal Disorder?
1. If there is a much larger number of
males than females who are affected
then the disorder is Sex-linked.
2. If there is a 50/50 ratio between males
and females who are affected then the
disorder is autosomal.
Slide # 10
Interpreting a Pedigree Chart
1. If it is autosomal disorder then ask:
Is it dominant or recessive?
2. If two parents do not show the trait and their
children do show it, then it is an autosomal
recessive disorder
- (parents are carriers or heterozygous)
3. If the disorder is autosomal dominant, then
at least one of the parents must show the
disorder.
Slide # 11
Note:
1. The following pedigree charts show affected
individuals only.
2. Carriers are unknown at this point.
Slide # 12
Practice Examples
Does this pedigree show a
Sex-linked or Autosomal disorder?
Answer:
Sex-Linked disorder
much larger number of
males are affected
Slide # 13
Practice Examples
Does this pedigree show a
Sex-linked or Autosomal disorder?
Answer:
Autosomal disorder 50/50
ratio between males and
females
Slide # 14
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
Slide # 15
Practice Examples
Does this pedigree show a
Sex-linked or Autosomal disorder?
Answer:
Autosomal disorder 50/50
ratio between males and
females
Slide # 16
Practice Examples
Does this pedigree show a Autosomal
Dominant or Recessive disorder?
Answer:
Autosomal recessive disorder
Two parents do not show the
trait but their children do show it
(heterozygous parents)
Slide # 17
Autosomal Recessive
Genotypes and Carrier determination
D = Normal hearing
d = deafness
Dd
dd
Dd
dd
Dd
dd
Dd
Dd
dd
dd
Dd
dd
D?