DNA Fingerprinting: Videos & Practice Problems

DNA fingerprinting utilizes genetic markers, specifically polymorphisms like single nucleotide polymorphisms (SNPs), to identify individuals. SNPs differ by a single nucleotide in DNA sequences among individuals. Additionally, short tandem repeats (STRs), which are 2 to 5 nucleotide-long repeated sequences, serve as unique genetic markers for identification. The variation in the number of STRs among individuals can aid in forensic investigations, such as solving crimes by comparing DNA samples from crime scenes to suspects.

DNA Fingerprinting

DNA fingerprinting is a powerful technique that utilizes genetic markers within a genome to identify individuals, similar to how traditional fingerprints are used. These genetic markers are specific sequences of DNA that have known locations and can be easily identified within a genome. The term "markers" often refers to polymorphisms, which are variations in DNA sequences that differ among individuals.

One common type of genetic marker is the single nucleotide polymorphism (SNP), which is a variation at a single nucleotide position in the DNA sequence. For instance, consider two individuals whose DNA sequences are nearly identical except for one nucleotide. In this case, if individual one has a thymine (T) at a specific position and individual two has a cytosine (C), this difference represents a SNP. Such polymorphisms are unique to each individual and serve as a basis for identification, much like a fingerprint.

A person's DNA fingerprint is essentially the combination of all their unique genetic markers, including various SNPs and other polymorphisms. This unique genetic profile can be used in various applications, such as forensic science, paternity testing, and genetic research. Understanding these concepts lays the groundwork for further exploration and practical applications of DNA fingerprinting techniques.

Short Tandem Repeats (STRs)

Short tandem repeats, commonly abbreviated as STRs, are crucial genetic markers used in various fields, including forensic science. STRs consist of short sequences of DNA, typically ranging from 2 to 5 nucleotides long, that are repeated in specific regions of the genome. The number of these repeats can vary significantly among individuals, making them polymorphic and unique identifiers for each person.

For instance, in a given region of DNA, one individual may have five repeats of a specific sequence, while another may have only three, and yet another may have four. This variability allows researchers and forensic experts to distinguish between different individuals based on their DNA profiles. In practical applications, such as crime scene investigations, STR analysis can be instrumental in matching DNA samples found at a crime scene with those of potential suspects.

To illustrate, consider a repeated sequence like "GATA." If three individuals are analyzed, their DNA might show the following counts of STRs: Individual 1 has five repeats, Individual 2 has three, and Individual 3 has four. This distinct pattern of STRs serves as a genetic fingerprint, enabling accurate identification and aiding in solving crimes.

As we delve deeper into the study of genetics, understanding STRs will be essential for applying these concepts in real-world scenarios, particularly in forensic analysis and genetic research.

The goal of DNA fingerprinting is:

• A. To collect DNA samples from random individuals in a population.
• B. To diagnose diseases within closely related family members.
• C. To determine whether DNA samples collected from two different locations are from the same person.
• D. None of the above.

Answer: (C)

Which of the following characteristics of short tandem repeats (STRs) makes it useful for DNA fingerprinting?

• A. The number of repeats is highly variable from person to person or organism to organism.
• B. The sequence of DNA that is repeated varies significantly from individual to individual.
• C. The sequence variation is acted upon differently by natural selection in different environments.
• D. Every racial and ethnic group has inherited a specific number of short tandem repeats.

Answer: (A)

The gel below shows a region of STRs from a DNA sample taken from a crime scene. It also shows the same region of STRs from 4 suspects involved in the case. Which suspect' DNA was found at the crime scene?

• A. Suspect 1.
• B. Suspect 2.
• C. Suspect 3.
• D. Suspect 4.
• E. They are all innocent.

Answer: (B)

Here’s what students ask on this topic:

What is DNA fingerprinting and how is it used in forensic science?

DNA fingerprinting is a technique that uses genetic markers within a genome to identify an individual. These markers, such as single nucleotide polymorphisms (SNPs) and short tandem repeats (STRs), are unique to each person. In forensic science, DNA fingerprinting is crucial for matching DNA samples from crime scenes to suspects. By comparing the genetic markers in the DNA found at a crime scene with those of potential suspects, forensic scientists can determine if there is a match, thereby helping to solve crimes and identify individuals involved.

What are single nucleotide polymorphisms (SNPs) and how do they contribute to DNA fingerprinting?

Single nucleotide polymorphisms (SNPs) are genetic markers that differ by just one nucleotide between individuals. These variations occur at specific positions in the genome and are unique to each person. In DNA fingerprinting, SNPs are used to identify individuals because the pattern of these single nucleotide differences is unique to each person. By analyzing SNPs, scientists can create a genetic profile that can be used to match DNA samples from different sources, such as crime scenes and suspects, making SNPs a valuable tool in forensic science.

What are short tandem repeats (STRs) and why are they important in DNA fingerprinting?

Short tandem repeats (STRs) are short sequences of DNA, typically 2 to 5 nucleotides long, that are repeated in tandem at specific locations in the genome. The number of these repeats varies among individuals, making STRs unique genetic markers. In DNA fingerprinting, STRs are important because their variability allows for precise identification of individuals. By comparing the number of STRs in DNA samples from crime scenes with those of suspects, forensic scientists can determine if there is a match, aiding in criminal investigations and identification processes.

How do forensic scientists use DNA fingerprinting to solve crimes?

Forensic scientists use DNA fingerprinting to solve crimes by comparing genetic markers in DNA samples from crime scenes with those of potential suspects. They analyze specific markers, such as single nucleotide polymorphisms (SNPs) and short tandem repeats (STRs), which are unique to each individual. By creating a genetic profile from the crime scene DNA and comparing it to the profiles of suspects, scientists can determine if there is a match. This process helps to identify or exclude suspects, providing crucial evidence in criminal investigations.

What is the difference between SNPs and STRs in the context of DNA fingerprinting?

In the context of DNA fingerprinting, single nucleotide polymorphisms (SNPs) and short tandem repeats (STRs) are both genetic markers used to identify individuals, but they differ in their structure and variability. SNPs are variations at a single nucleotide position in the genome, while STRs are short sequences of DNA, 2 to 5 nucleotides long, that are repeated in tandem. The number of repeats in STRs varies among individuals, making them highly polymorphic. Both SNPs and STRs are used to create unique genetic profiles for individuals, aiding in forensic identification and criminal investigations.