DNA Typing Simulation: Practice Problems
Name __________________________
Date________ Period_____ Group_____
For each person in our simulation, the “cut” DNA represents pieces of DNA cut from the same locus
(place) on each of two chromosomes (a homologous pair). These DNA pieces may be the same length
or different lengths. We used a restriction enzyme, Hind III, to cut the DNA into these allele fragments.
Gel electrophoresis is a process we will use to separate the DNA pieces according to their length. After
running them on a gel, DNA pieces of the same length can be collected together at one spot on the gel.
After staining the DNA we will be able to see comparative lengths of DNA from each person. In this
simulation, each allele is represented by a band made of many copies of a DNA fragment of a certain
length.
The purpose of this practice problem set is to help you think about what you are doing during this lab
simulation and to learn to analyze the results.
Use the following key to identify persons whose DNA bands are represented on these gels:
M0 = Mothers DNA, uncut
M+ = Mothers DNA, cut
B0 = Baby’s DNA, uncut
B+ = Baby’s DNA, cut
S0 = Suspects DNA, uncut
S+ = Suspects DNA, cut
PART I – ANALYZING THE GEL
1. A. How many bands representing different sized pieces of DNA would you expect if a person is
homozygous for the DNA location (or alleles) being examined? Explain your answer. (Homozygous =
same allele on each member of a chromosome pair)
B. How many bands representing different sized pieces of DNA would you expect if a person were
heterozygous for the DNA location (or alleles) being examined? Explain your answer. (Heterozygous
= different alleles on each member of a chromosome pair)
2. Remember: For a given trait, a child receives one allele from each
parent.
A. Draw a gel showing DNA bands from a child who is
heterozygous for the given trait. You can put DNA bands
wherever you want on the gel.
B. Now draw bands representing one possible DNA makeup
for the Mother of that child, and one possible DNA
makeup for the father.
C. Be prepared to explain your answers.
Gel #1
PART II – UNEXPECTED RESULTS
3. Sometimes the results of a test are not what was expected. Consider and offer the explanations for
the results shown on gels #2, #3 and #4. Write your answers next to each gel.
M+
B+
S+
M+
Gel #2
B+
S+
Gel #3
PART III – ALLELE FREQUENCIES
M+
B+
S+
Gel #4
M+
B+
S+
4. A. Look carefully at gel 5. Is the suspect included or excluded? Explain
you answer.
B. Consider the Father’s DNA: What is the percent chance that
someone else has a band the same size as band #2?
(Note: In a sample 1000 people, you find that 50 people
have a band the same size as #2.)
5. Read the information below about two different cases. Which case offers
the strongest evidence? Explain.
Gel #5
Case I:
DNA Fingerprinting indicates inclusion of the suspect because of the matching of a particular allele
with an allele frequency of 30%.
Case II:
DNA Fingerprinting indicates inclusion of the suspect because of the matching of a different allele
with an allele frequency of 1%.
6. Imagine that you have been selected to be on a jury. The case you are considering includes DNA
typing evidence to help convict the suspect. As the case proceeds, a fellow juror asks you “I have never
heard of DNA typing… what is it?” Explain how you would answer this question to help your colleague
understand the science behind DNA typing and how it can be used to include or exclude a suspect.