How to Read a Pedigree Chart
Pedigree is a chart that shows relationships within a family. Like a family tree
They are used to study how traits are passed from one generation to the
next
Legend
Male
Generation
Female
Male Carrier
(heterozygous)
Female Carrier
(heterozygous)
Male that has a trait
Female that has a trait
Autosomal Dominant
Autosomal Recessive
X-linked Dominant
X-linked Recessive
All daughters of a male who has the
trait will also have the trait
There is no male-to-male
transmission
A female who has the trait may or
may not pass the gene for that trait
to her son or daughter
Males and females are equally likely
to have the trait.
Traits do not skip generations
(generally)
The trait is present whenever the
corresponding gene is present
(generally)
There is male-to-male transmission
Males and females are equally likely
to have the trait
Traits often skip generations
Often, both parents of offspring who
have the trait are heterozygous (they
carry at least one copy of the allele)
Only homozygous individuals have
the trait
Traits may appear in siblings without
appearing in their parents
If a parent has the trait, those
offspring who do not have it are
heterozygous carriers for the trait
The trait is far more common in
males than in females
All daughters of a male who has the
trait are heterozygous carriers
The son of a female carrier has a 50%
chance of having the trait
There is no male-to-male
transmission
Mothers of males who have the trait
are either heterozygous carriers or
homozygous and express the trait
Daughters of female carriers have a
50% chance of being carriers
Practice: Pedigrees
1.
2.
3.
4.
5.
6.
7.
8.
If the daughter in the third generation married a carrier of the trait. What is the probability that
their children will have the trait?
Sometimes you are only shown if an individual is recessive or dominant. You will have to figure out who are the
carriers.
1. Free ear lobes are a dominant trait while attached ear lobes are recessive. The shaded regions show individuals
who are homozygous recessive for attached ear lobes. Use the symbols E and e to label the genotypes of the
individual.
2. Sickle cell anemia is a recessive trait. The shaded individuals exhibit this trait and are therefore homozygous
recessive. Determine the genotype of all the individuals.
Solve it: Analyzing Pedigrees
Below is a pedigree for a group of dogs. Some of the dogs in this group are tall, some are short. Some are tall but
carry the recessive short trait. White individuals are tall dominant. Shaded individuals are short recessive.
1. How many generations are shown in the pedigree?
2. How many offspring did the parents in the first generation have?
3. What does the square in generation one stand for? Why is it half-shaded?
4. Which dog was the first in the family to be short?
5. A female dog from generation three has four puppies. How many of these offspring carry the short trait? How many of
the offspring are short?
Analyze the pedigree shown for sickle-cell anemia, a recessive blood disorder.
2
1
2
5
4
3
6
7
16
15
9
8
17
18
10
19
11
20
12
21
13
14
22
23
24
1. How many generations are represented in the pedigree?
2. In generation one, which parent is heterozygous for the recessive allele?
3. Which individual is generation two marries a spouse who is homozygous dominant?
4. In which generation does the first case of sickle cell anemia appear?
5. Which generation contains the most male carriers?
6. Can two carriers produce an individual with sickle cell anemia?
7. Can a normal homozygous individual produce offspring with sickle cell anemia?
8. Which parents produce two children with sickle cell anemia?
25
26