Download Pedigrees

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. Pedigree chart traces the inheritance of a
particular trait through several generations.
2. One GOAL of using a pedigree chart is to
determine carriers and the likelihood that
future generations could be affected.
Carrier: someone who carries the gene but
is unaffected by the genetic disorder. The
person must be heterozygous and the trait
recessive.
Slide # 3
Constructing a Pedigree
Female
Male
Slide # 4
Constructing a Pedigree
1. 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 child, in order
of birth from left to right.
Slide # 5
Constructing a Pedigree
1. Fraternal twins- (same or different
gender)
a. Two line branching from the
same point
b. Two different eggs and two
different sperm cells.
2. Identical twins (same gender)
a. Similar to fraternal twins with an
additional horizontal line.
b. One egg and one sperm unite
and later splits to create two
babies
Generations
Slide # 6
1. Roman numerals indicate 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:
Affected with the disorder
2. Half shaded:
– Carrier (recessive)
3. 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 probably Sexlinked.
2. If there is a 50/50 ratio between males
and females who are affected then the
disorder is likely autosomal.
Slide # 10
Interpreting a Pedigree Chart
If it is autosomal disorder then ask:
Is it dominant or recessive?
Does the trait skip a generation anywhere on the
pedigree? If so, recessive. If not, the trait MAY be
recessive.
1. 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)
2. If the disorder is autosomal dominant, then at least
one of the parents must show the disorder.
Slide # 11
Note:
 The following pedigree charts show affected
individuals only.
 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)
Now Draw…
 Sketch the next pedigree onto your
notebook.
 Write the genotypes below the individuals.
 Individuals affected will be dd.
 Color in carriers (color half of the shape)
 Title with the appropriate words…
– Autosomal vs . Sex-linked
– Dominant vs Recessive
 DON’T SCROLL AHEAD UNTIL YOU’VE
TRIED THE PEDIGREE!!!
 WHAT IS D?
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?