Although the base sequence of most human DNA is identical from one person to another, there are sufficient differences to…

Although the base sequence of most human DNA is identical from one person to another, there are sufficient differences to enable use of this information to identify individuals. These differences in the sequence of bases in DNA from one individual to another lead to differences in the distribution and frequency of restriction enzyme recognition sites. Thus, when an individual’s DNA is fragmented with a specific restriction enzyme, the number and length of the resulting fragments is unique (unless the individual has an identical twin). The different length DNA fragments are called restriction fragment length polymorphisms, or RFLPs (pronounced Ríf-lips) for short.

 

After studying Figure 1, answer the following questions.

 

1)      How many RFLPs are generated from homologue M using this restriction enzyme? from homologue P?

2)      Explain this difference.

3)      Are the DNA segments in the diagram an entire chromosome? an entire gene? Explain.

 

                                                                  Figure 1.

 

A.  A Restriction Enzyme and its Cleaving Sequence

Enayme:  SalI derived from Streptomyces albus. This enzyme cuts DNA between G and T on the upper strand, between T and G on the lower strand, and horizontally between the two cuts.

 

Cleavage Sequence: 

          5 G T C G A C 3                               5 G                                         T C G A C 3 

          3 C A G C T G 5                  3 C A G C T          and                         G5

 

B.  Restriction Site Differences Between Two Homologous Chromosomes Using SalI

                 Homologue M                                                         Homologue P

 

A G G C G T C G A C G A G T C G A C T          A A G G C G T C G A C G A T T C G A C T

T C C G C A G C T G C T  C A G C T G A           T T C C G C A G C T G C T A A G C T G A

 

PART V. SOLVING A CRIME USING DNA (RFLP) FINGERPRINTS

 

One evening the police responded to a report of gunshots. Arriving at the scene, the officers found a parked pickup truck. In the passenger seat was a deceased male with several gunshot wounds. Footprints were visible in a pool of blood outside the truck, but they were not clear enough to identify the type of footwear that made them. Homicide detectives have narrowed the field to three suspects.

 

Suspect A was arrested near the scene and acknowledged knowing the victim. He was wearing black work boots that appeared to have dried blood on the soles.

 

At the home of suspect B, investigators recovered a pair of tennis shoes that also appeared to have dried blood on the soles. Suspect B says she had a severe nosebleed, which may have resulted in blood on her shoes.

 

Suspect C was the roommate of the deceased. When officers went to the apartment to notify him of the death, suspect C was packing a suitcase.  He was wearing sneakers that appeared to have dried blood on the soles and sides. When questioned about the blood and the murder, suspect C had no comment.

 

All the samples were tested and identified as human blood. The homicide detectives have asked the molecular biology laboratory to analyze the blood evidence using DNA fingerprint analysis. You are the forensic scientist assigned to the case. Figure 2 shows the DNA profiles from all the blood samples.

 

1.      Note that the box under the first column in Figure 2 (blood of victim) contains the number 1. This is the first unique DNA profile found.

2.      Moving from left to right, examine each DNA profile.

If the new profile does not match any previously examined profile, enter a new number in the box under the column (2,3,4 etc.).

If the new DNA profile is an exact match of a previous profile, enter the number you gave to the profile that matches this new profile.

Continue with this process until you have examined all the DNA profiles in Figure 2.

 

Questions:

1)      How many unique profiles were found?                

 

2)      Did any profiles match the blood from suspect A’s shoes?             If so, list them:                      

 

3)      Did any profiles match the blood from suspect B’s shoes?             If so, list them:                        

 

4)      Did any profiles match the blood from suspect C’s shoes?              If so, list them:                     

 

5)      Did any profiles match the blood from the deceased male?             If so, list them:                     

 

6)      Did any profiles match the blood found on the ground outside the truck?           

       If so, list them:                   

 

7)      Do these results make any individual a more likely suspect that the others?                     

 

8)      Explain your answer, citing facts from the DNA analysis.

 

 

 

Blood of victim

Blood on ground at scene

Blood of suspect A

Blood of suspect B

Blood of suspect C

Blood from suspect A’s shoes

Blood from suspect B’s shoes

Blood from suspect C’s shoes

1

 

 

—–

 

—–

—–

 

 

2

—–

—–

 

 

 

 

 

—–

3

—–

—–

 

 

—–

 

 

—–

4

 

 

—–

 

 

—–

 

 

5

 

 

—–

—–

 

—–

—–

 

6

 

 

 

—–

—–

 

—–

 

7

—–

—–

 

—–

 

 

—–

—–

8

 

 

 

 

—–

 

 

 

9

 

 

—–

 

—–

—–

 

 

10

—–

—–

 

 

 

 

 

—–

11

 

 

 

—–

 

 

—–

 

12

 

 

—–

 

—–

—–

 

 

13

 

 

 

—–

 

 

—–

 

14

 

 

 

 

 

 

 

 

15

—–

—–

 

 

 

 

 

—–

16

—–

—–

 

 

 

 

 

—–

17

 

 

 

 

 

 

 

 

18

 

 

 

—–

 

 

—–

 

19

 

 

 

 

 

 

 

 

20

—–

—–

—–

 

 

—–

 

—–

 

1

 

 

 

 

 

 

 

                                    Figure 2. DNA Profiles – Homicide case AF205

0 replies

Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *