1. Bio 103 - Introduction to Biology
Chapter 9: Patterns of Inheritance
Pedigrees
Background: Geneticists cannot study people in the same way in which they study other organisms. Since
humans choose their own mates, geneticists cannot conduct breeding experiments to determine how human
traits are inherited. In addition, humans have a long life span. As a result, it takes many years to produce
several generations. Finally, most human families have small numbers of offspring, too few to verify the
outcomes of crosses predicted by probability.
To overcome these problems, geneticists use special techniques. Three of the most common methods used are:
a. pedigree analysis
b. population sampling
c. twin studies
In this worksheet we will limit our study to pedigree analysis. A pedigree is a record that shows how a trait is
inherited over several generations. It is like a family tree but more specific because it represents more than
just names of individuals. By analyzing pedigrees, one can learn how the character and location of a genetic
trait is distributed within families. When genotypes are known then predictions can be made about potential
genetic problems. Pedigrees are based on the observable phenotypes; for in them are the clues to genotypes.
Below is a sample pedigree. Try to determine if the trait indicated in the pedigree is dominant or recessive. Is
the trait autosomal or sex linked? Use the key to better understand the symbols. Using the letters M for
normal allele and m for muscular dystrophy, try to assign each individual two alleles. Base your letters on the
phenotypes indicated in the pedigree.
The pedigree shown above is one for a disorder called Duchenne muscular dystrophy in which the muscles grow
progressively weaker. The disease is caused by a recessive gene found on the X chromosome. Traits found on
the X chromosome are called sex linked and will be more common in the male than the female.
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success = preparation + execution

2. Objectives:
To learn how to evaluate and use pedigrees to solve genetic problems.
Procedure:
Examine the following pedigree. Based on the given phenotypes, fill in as many of the alleles as possible. Use
the small c for Cream and large C for Dark fur color.
PEDIGREE 1: FUR COLOR IN VOLES; SEGREGATION AND DOMINANT/RECESSIVE ALLELES
Analysis:
1. Which fur color is dominant? What evidence do you see to support your conclusion?
2. What symbol is used to represent a female in pedigrees?
3. List each genotype, 1 through 14, for each individual within the pedigree.
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success = preparation + execution