DNA Fingerprinting - Online Tutor, Practice Problems & Exam Prep

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

In this video, we're going to begin our lesson on DNA fingerprinting. DNA fingerprinting is really just a specific technique that uses genetic markers within a genome to identify an individual. Just like a fingerprint can be used to identify an individual, like the fingerprint that we have down below right here, DNA fingerprinting can help to identify an individual.

What are these genetic markers? Genetic markers are sequences of DNA with a known location that are easily identifiable in a genome. Markers specifically refer to polymorphisms. Polymorphisms are completely different between the genomes of each individual, so they represent 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 this example image down below, we're looking at how a single nucleotide polymorphism can exist between two alleles within the same organism across two different individuals. If we take a look at this image down below, you'll notice we have individual number 1, which is right here, and this is the specific DNA sequence of individual number 1. Down below, we have individual number 2, whose sequence is right here. 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 here 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 differs 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. 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. And so genetic markers used by researchers are generally made up of short repeat sequences that vary in number. And so these are referred to as short tandem repeats, which again are commonly abbreviated as just STRs. And so these short tandem repeats or STRs are short repeated sequences of DNA that are approximately 2 to 5 nucleotides long. Nts is an abbreviation for nucleotides, and they're found in very specific regions of a genome. Now the specific number of STRs or short tandem repeats within this region of a genome is polymorphic, which means that it is going to be unique for each person and each individual and can be used to identify an individual. And so here in this example image down below, we're showing you just some examples of short tandem repeats. And so short tandem repeats or STRs are genetic markers that can be used to identify an individual, perhaps, identifying the individuals, by using DNA that's found at a crime scene. And so it can be used to help solve a crime.

And so if we take a look at this image down below, notice that the repeated sequence, the short, tandem repeat that we're looking at is, this sequence right here where it is g a t a. Okay? And so this is the, double stranded DNA and the short tandem repeat that we're specifically focusing on in this image. And so what you'll notice is that we've got DNA from 3 different individuals down below. Individual one's DNA is here. Then we have individual 2, their DNA is there, and individual three's DNA is at the very bottom. And what you'll notice is that at this very specific region of interest in the chromosome, each of these 3 individuals differ in their number of short tandem repeats or STRs. And so what you'll notice is that individual number 1 has a total of 5 STRs, five short tandem repeats, which would be unique to this specific individual number 1. Individual number 2, notice it only has 3 of these short tandem repeats within this region of the genome. And that 3 would be unique to individual number 2. And individual number 3 has a total of 4 short tandem repeats. And so the number of short tandem repeats is going to be unique for each individual and is going to be a genetic marker that can be used to, again, identify an individual and can be used to, basically help solve a crime by comparing the, the DNA that might be found at the crime scene with the DNA from the suspects.

And so, this here 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 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.