Name: _____________________________________ Date: _________________ Block: __________
Exploring Autosomal Pedigrees
You can look at a pedigree and determine whether traits are dominant or recessive, and you
can also tell if it is sex-linked or autosomal. Sex-linked traits are carried on the sex chromosomes (X
or Y). Autosomal traits are carried on chromosomes 1 to 22. Use the guided steps below to unveil
the patterns in pedigrees. In the pedigree below, we will explore the autosomal trait for dimples.
Having no dimples is dominant to having dimples.
A. Interpreting a Pedigree
1. Number all individuals on the pedigree
at the top of each circle or square.
I
2. In a pedigree, a square represents a male.
If is it darkened he has dimples. If the square is
open, he does not have dimples.
II
a. How many males are there? _______________
1
2
III
b. How many males have dimples? ____________
3. A circle represents a female. If it is darkened she
has dimples. If it is open, she does not have
dimples.
IV
a. How many females are there? ______________
b. How many females have dimples? ___________
4. A marriage is indicated by a horizontal line connecting a circle to a square.
a. How many marriages are there? _____________
5. A line perpendicular to a marriage line indicates the offspring. If the line ends with either a circle
of a square, the couple had only one child. However, is the line is connected to another horizontal
line, then several children were produced, each indicated by a short vertical line connected to the
horizontal line. The first-born child appears to the left and the last-born child appears to the right.
a. How many children did the first couple have (couple in row I)? _____________________________
b. How many children did the third couple have (couple in row III)? ___________________________
6. Level I represents the first generation and level II represents the second generation.
a. How many generations are there? _____________
b. How many members are there in the fourth generation? ______________
B. Determining the Pattern of Inheritance and Assigning Genotypes
When working through a pedigree, you must determine whether the trait (the shaded shapes) is
dominant or recessive. This involves the “guess and check” method. With no other information
aside from the pedigree, you may find that the trait could be passed BOTH ways. Choose a letter
(let’s use A) and begin assigning genotypes. Remember that they recessive individuals must be
homozygous.
Complete the legend for the following pedigree regarding fur color in mice. All of the shaded shapes
represent black fur color. All of the open shapes represent white fur color.
=
=
=
=
Let’s start by testing whether or not black fur color is inherited as a DOMINANT trait (AA or Aa).
Label each individual. If all genotypes can be labeled, the trait is inherited that way. You may have
indivudals that you cannot tell (nor does it matter) whether they are AA or Aa. In this case, label
them as (A-) (Hint: You will have 3 (A-)s in the pedigree below.)
Fur Color in Mice
1. Is black fur color a dominant trait? ________________________
Let’s try it again, but check and see if black fur can also be a recessive trait (aa).
2. Is black fur color a recessive trait? ___________________________
Still not quite sure about how to label genotypes? Search for the following video on YouTube,
Pedigree Analysis 1: How to solve a genetic pedigree No. 1. It is By Andrew Douch and
should be 9:13 minutes long. Start at MINUTE 5. He works through sex-linked options as well, but
you are not responsible for knowing this. This video will work on your cell phone.
C. Create Your Own Pedigree
In the space below, use colored pencils to create a pedigree with the following information. Follow
the guidelines for a pedigree when creating your own.
Ray and Elaine were married in 1970. They both have straight hair. Straight hair is the dominant
allele over curly hair. Ray and Elaine had 2 daughters and then a son. The first born daughter,
Candace, has curly hair. The second born daughter, Judy, has straight hair. Neither daughter is
married yet or has children. The son, Mike, has curly hair. Mike married Alisha, who has straight
hair. They had 2 children of their own, first Greg then Nicole. Both Nicole and Greg have straight
hair. Create a pedigree. Label the names and genotypes for each individual.
Use the following key to color your pedigree:
Red = Curly Hair
White = Straight Hair
Blue = Heterozygote
Green = Unknown Genotype