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.
DNA Fingerprinting - Video Tutorials & Practice Problems
DNA Fingerprinting
Video transcript
Short Tandem Repeats (STRs)
Video transcript
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:
Which of the following characteristics of short tandem repeats (STRs) makes it useful for DNA fingerprinting?
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?