Pedigree
Recessive and Dominant traits can be traced through a family using a chart called a family pedigree.
On this chart Males are represented by using
squares. Females are represented by using
circles. A line between individuals represents a marriage or a union that results in children.
Children are drawn as a line descending from this line.
If there is more
than one child from this union they are shown as a line across this descending line with
descending lines for each child.
The oldest child will be on the left. The youngest child will be on the right.
Each student’s pedigree should cover three generations. They will be in the third generation.
One of their parents (either Mom or Dad) will be in the second generation along with their (Mom’s or
Dad’s) brothers or sisters. The first generation will be their grand parents on either Mom’s or Dad’s side.
Grandparents
Uncle
Dad
Cousin
Student
Aunt
Brother
Cousin
A student trait is represented by shading the circle or square. The color green = Not a tongue
roller
What the trait looks like is called the phenotype. Brown hair is a phenotype it tells us what the person’s
body looks like when the directions on the DNA were followed. The genotype is the letters we use to
trace how the genes from the parents are passed to the children. Brown hair would be shown by the use of
letter such as BB or Bb.
The genotypes are shown by using lower case letters to show the recessive trait and upper case letters to
show the dominate trait.
BB = brown hair, this person has two dominate genes
Bb = brown hair because the B gene from one parent dominates the b gene from the other parent
bb = blonde hair, you must have two recessive genes to show a recessive trait
tt
Tt or TT
The students pedigree should have the phenotype shown on their pedigree chart by the use of shading to
show their trait and a Key that tells what it looks like
Key
No freckles = my recessive trait
Freckles = dominate trait
Females
Males
Using a pedigree to trace your genotype:
On our DNA we all have a gene for freckles or no freckles. Our DNA has two strands so
we have two copies of each gene. This gives our bodies a backup copy in case of a damaged gene. It
allows for more variety a white chicken and a black chicken might have a co-dominate gene for color
creating some offspring that look grey. Each parent gives a child a copy of one of the two genes they
have in their DNA.
= recessive trait for no freckles
ff
This parent has two genes for the recessive trait for no freckles, if they had even one dominate
gene they would have freckles. When this parent creates sex cells for producing offspring he can only
give recessive genes to those sex cells.
ff
f
f
ff
f
f
f
Dad give each of his children one of his two recessive genes. Now how do we use the pedigree to
Tell what mom’s genotype is? If a child has a recessive trait, they must have gotten a recessive
trait from each of their parents.
ff
f
Ff = Mom must be Ff because she has freckles and
gave her daughter a recessive gene
f
ff
Both of the boys in the pedigree must be Ff because they have freckles so they must have a
dominate gene and they had to get a recessive gene from their father
ff
Ff
Ff
Ff
ff
Sometimes we can’t tell if a person is FF or Ff. In that case we list both below the person on the
chart
ff
Ff
FF
Ff
FF
Ff
Ff
Ff
ff
We don’t have a family pedigree to know the genotype of this
child’s wife, but we know she has at least one dominate gene
because she has freckles. Their child could be FF if he received a
Dominate gene from both parents or could be Ff if he received one of each. He can’t be ff
because he has freckles.
ff
Ff
FF
Ff
Ff
Ff
Ff
ff
Ff
FF
ff
Ff
ff
Using the same rules listed above we can now figure out that the wife of the second son is Ff
because she had to have given a recessive gene f to her daughter and the same is true for the husband of
the third child. The last grandson is left to figure out. This child has freckles, but he could have a
dominate gene from either parent or a recessive gene from either parents. Therefore he could be FF or Ff.
Here we have
Tom Lee’s Spotted Family Pedigree
ff
Ff
FF
Ff
FF
Ff
Key
No freckles = my recessive trait
Freckles = dominate trait
Females
Males
Ff
Ff
Ff
ff
Ff
ff
ff
FF
Ff