DNA Fingerprinting - Online Tutor, Practice Problems & Exam Prep

DNA fingerprinting utilizes genetic markers, specifically polymorphisms like single nucleotide polymorphisms (SNPs), to identify individuals uniquely. These markers differ among individuals, similar to traditional fingerprints. Short tandem repeats (STRs), which are 2 to 5 nucleotide-long sequences, also serve as genetic markers, varying in number across individuals. Both SNPs and STRs are crucial in forensic science for identifying suspects through DNA evidence found at crime scenes, highlighting their importance in genetic identification and criminal investigations.

DNA Fingerprinting

This video, we're going to begin our lesson on DNA fingerprinting. DNA fingerprinting is really just a specific technique that is going to use genetic markers within a genome to identify an individual. Just like a fingerprint can be used to identify an individual, DNA fingerprinting can help to identify an individual. What are these genetic markers? Genetic markers are sequences of DNA with a known location and are easily identifiable in a genome. Markers specifically refer to polymorphisms, and polymorphisms are completely different between the genomes of each individual, so they're differences in the sequence across different individuals. For example, single nucleotide polymorphisms, which are commonly abbreviated as SNPs, are genetic markers in a genome that differ by just one single nucleotide across different organisms. If we take a look at an example image, we're looking at how a single nucleotide polymorphism can exist between 2 alleles within the same organism across 2 different individuals. In this image below, what you'll notice is that we have individual number 1, which is right here, and this is the specific DNA sequence of individual number 1. Below, we have individual number 2, whose sequence is right here. And what you'll notice is that the DNA sequence of individual 1 and individual number 2 are pretty much exactly the same, except for one position of this base pair. This would be referred to as a single nucleotide polymorphism or a SNP because it's just this one position here that is going to differ between the two, where individual one has a TA base pair at this position, whereas individual 2 has a CG base pair. These polymorphisms are going to be unique to specific individuals and can be used to help identify an individual just like a fingerprint can be used to identify an individual. Now, a person's DNA fingerprint is really just referring to the combination of all the unique genetic markers in an individual's genome. This here concludes our brief introduction to DNA fingerprinting and how these unique genetic markers and polymorphisms can be used to help identify an individual. We'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Short Tandem Repeats (STRs)

In this video, we're going to introduce short tandem repeats, which are commonly abbreviated as STRs. These genetic markers used by researchers are generally made up of short repeat sequences that vary in number. These repeats are referred to as short tandem repeats, or STRs, which are short repeated sequences of DNA that are approximately 2 to 5 nucleotides long. Nucleotides, abbreviated as Nts, are found in very specific regions of a genome. The specific number of STRs in this region of a genome is polymorphic, meaning that it is unique for each person and can be used to identify individuals. Here in this example image below, we are showing you some examples of short tandem repeats. Short tandem repeats, or STRs, are genetic markers that can be used to identify individuals, perhaps by using DNA found at a crime scene. These markers can help solve a crime.

Let's take a look at the image below. Notice that the repeated sequence, the short tandem repeat we are focusing on is the sequence 'g a t a'. This is the double-stranded DNA and the specific short tandem repeat in focus. You will notice DNA from three different individuals below. Individual one's DNA is here; then we have individual two, their DNA is there, and individual three's DNA is at the bottom. In this specific region of interest in the chromosome, each of these three individuals differs in their number of short tandem repeats or STRs. For instance, individual number one has a total of 5 STRs, which is unique to this specific individual. Individual number two has only 3 of these short tandem repeats within this region of the genome, which is unique to them. Individual number three has a total of 4 short tandem repeats. The number of short tandem repeats is unique for each individual and serves as a genetic marker that can be used to identify an individual and help solve a crime by comparing DNA that might be found at a crime scene with the DNA from suspects.

This concludes our brief introduction to short tandem repeats or STRs, and we'll be able to get some practice applying these concepts as we move forward in our course. So, I'll see you all in our next video.

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.

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.

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.

Here’s what students ask on this topic:

What is DNA fingerprinting and how is it used to identify individuals?

DNA fingerprinting is a technique that uses genetic markers within a genome to uniquely identify an individual. These genetic markers, such as single nucleotide polymorphisms (SNPs) and short tandem repeats (STRs), vary between individuals. SNPs are differences in a single nucleotide, while STRs are short sequences of DNA that repeat a variable number of times. By analyzing these polymorphisms, scientists can create a unique DNA profile for each person. This method is widely used in forensic science to match DNA from crime scenes with suspects, as well as in paternity testing and genetic research.

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

Single nucleotide polymorphisms (SNPs) are genetic markers that differ by a single nucleotide between individuals. For example, at a specific position in the DNA sequence, one person might have an adenine (A) while another has a cytosine (C). These variations are unique to each individual and can be used to create a DNA fingerprint. In DNA fingerprinting, multiple SNPs are analyzed to generate a unique genetic profile, which can be used for identification purposes in forensic science, paternity testing, and genetic research.

What are short tandem repeats (STRs) and why are they important in forensic science?

Short tandem repeats (STRs) are short sequences of DNA, typically 2 to 5 nucleotides long, that repeat multiple times in a row. The number of these repeats varies between individuals, making STRs useful genetic markers for identification. In forensic science, STR analysis is used to compare DNA samples from crime scenes with those of suspects. By examining the number of repeats at specific STR loci, forensic scientists can create a DNA profile that is unique to each individual, aiding in criminal investigations and legal proceedings.

How do genetic markers like SNPs and STRs differ in their application in DNA fingerprinting?

Both SNPs and STRs are used as genetic markers in DNA fingerprinting, but they differ in their characteristics and applications. SNPs involve a single nucleotide difference in the DNA sequence, making them highly specific and useful for fine-scale genetic analysis. STRs, on the other hand, consist of short sequences that repeat a variable number of times, providing a broader range of variation. While SNPs are often used for detailed genetic studies and ancestry testing, STRs are more commonly used in forensic science for creating DNA profiles due to their high variability and ease of analysis.

How is DNA fingerprinting used in criminal investigations?

In criminal investigations, DNA fingerprinting is used to match DNA evidence from a crime scene with potential suspects. By analyzing genetic markers such as SNPs and STRs, forensic scientists can create a DNA profile from the evidence. This profile is then compared to the DNA profiles of suspects. If a match is found, it can provide strong evidence linking a suspect to the crime scene. DNA fingerprinting is a powerful tool in solving crimes, identifying victims, and exonerating innocent individuals.