STR (Short Tandem Repeat) Analysis and DNA Fingerprinting Example | Genetics

In this video I go over the background of STR analysis and how it is used for things like crime scene analysis and maternal/paternal tests. I give a quick background, go over PCR (polymerase chain reaction), gel electrophoresis, and then check out two examples.
If you have any questions, let me know in the comments. Thanks and hope you enjoy!
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[@DrWD40]

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[@kuotesforu]

18 minutes of Pure and easy to understand Knowledge 🎉❤

[@kmacdowe]

Thanks! Clear, concise, easy to understand description of a complex subject.

[@subhashjuneja1689]

That was very clearly demonstrated in a very simple language. Thanks

[@meroproductions]

Thank you for helping me pass t forensics test

[@areebahassan6540]

THANK YOU SIR. THIS WAS REALLY HELPFUL.

[@rabiaselli2073]

Thanks.Really good explanation.

[@DrWD40]

You're welcome! Glad you enjoyed it

[@QkasperZ]

how can we do a gel electrophoresis for different loci on a single gel 16:45 ? is it possible only if the 3 different loci contains alleles with different length? (as shown in your video where locus 3 has the shortest as it is the furthest and locus 1 has the longest as they are near the negative pole) if the str has almost similar length, do we need to do it like the crime scene gel electropherosis?

[@DrWD40]

It depends how similar in length they are. You might need to change the gel concentration and pore size for a finer strand separation to separate those bands.

[@arjan8005]

Awesome video. I was just wondering how would you design a primer so that it would bind to the start of the STR and not in the middle or near the end since the STR is just repeated base pairs. Thanks :).

[@DrWD40]

Before and after the repeat sequences there are just normal random bases. Part of the reasoning behind using the STRs we choose is the primer selection. Forward and reverse primers need to be designed to have similar annealing temperatures.

[@arjan8005]

@@DrWD40 Okay thats great, cheers :).

[@yogeshkmrful]

Very nice video! helped me in my presentation

[@TheCortymast]

I just don't understand how exactly we only multiply the STR when performing PCR. Shouldn't the Taq polimerase just keep on running and duplicate the whole genome?

[@DrWD40]

The forward and reverse primers determine the ends since that's what Taq starts. It requires that primer and won't elongate any open segment of a strand.

[@annelisse16]

This was amazingly helpful

[@dheerutiwari2771]

Awesome video

[@shimaagaber8641]

جزاكم الله خيرا

[@pbraise1887]

Hi ! What’s the interest to create billions dna fragment with PCR if we just use one of them for paternity test ? And I don’t understand why is it necessary to use gel electrophoresis ? Aren’t all the fragments the same ? Thank you

[@DrWD40]

You need lots of fragments for them to appear on the gel when you stain them. The more DNA you have, the better the resolution on the gel. Fragments should be different sizes between individuals because the amount of repeats vary from person to person.

[@uwimbabaziglorieuse271]

I don’t understand how we get the STR sequence without cleaving it out of the genome using the restriction enzymes.

[@DrWD40]

The PCR primers do that for us after a few cycles.

[@eatonashton4962]

very clear and helpful. Thx! :)

[@europhile2658]

good video but you have not explained the relationship between Alleles and STRs. Is an STR an Allele? or does an Allele contain multiple (or one) STR? thanks

[@DrWD40]

Yup! An STR is an allele. The number of repeats within the STR defines the allele.

[@drsanchitadey-rh1zt]

@@DrWD40 I a

[@danielafrausto9354]

When does the Taq polymerase know when to stop? Like how do you isolate just the STR from the rest of the bp?

[@DrWD40]

You have a forward primer and a reverse primer that flank the STR. After a few cycles you'll only have the STR region with the flanking forward and reverse primary.

[@cynthiarodriguez7395]

Can we use 2 or 3 different set of primers to detect different STRs in the same reaction so we can have more bands in the same well of the gel? I would like to try making one of those personalized dna profiling portraits/canvas they sell online, like in dna11.com . Is this the correct way of doing it or what would you suggest? Thanks !

[@DrWD40]

Possibly. Each primer has a slightly different annealing temperature so you'd want to design them to be as close as possible. When I did genotyping on transgenic mice I had to run my PCRs separately because the annealing temps were too different.

[@chubiin20s]

EXCELLENT

[@kaorbo]

How likely is it that a father and sons would show as a match to a dna sample ran through str pcr by sled?

[@DrWD40]

The mother would also have to match at least the half the father gave.

[@marcosgrove6296]

Pls, answer my question. So can we conclude that STR use multiple-locus marker? coz the markers represent various loci along the genome. or STR using single-locus marker? bcoz at the first analyze, we only investigate single-locus that similar to our suspect, every variation that we generated is represented different allele in the investigated locus. Please answer this I got so confused STR belong to single-locus or multiple-locus?

[@DrWD40]

There are 13 CODIS core loci that they can choose from. Here they are with some more info www.barnardhealth.us/forensic-science/the-13-codis-str-loci.html

[@knockoutthehurdles5305]

Can we detect individuality of same male through Mt dna str analysis

[@darrein3185]

It is possible to know the unique combinations for a STR?

[@DrWD40]

What do you mean by the unique combinations? Like how many repeat variations are there for a certain STR?

[@knockoutthehurdles5305]

Same family male individuality through Mt dna str analysis

[@DrWD40]

Mitochondrial DNA will only come from the mother. Not sure what your question means.

[@knockoutthehurdles5305]

Sir ,actually my question is that can we use Mt dna of same family member to distinguish male members through str

[@DrWD40]

With mitochondrial DNA, you can only confirm when compared with the mother or a sibling from the same mother.

[@knockoutthehurdles5305]

Tq sir ,we can't do str analysis by using Mt dna of same family in criminal cases

[@khalidmusallam1757]

Does str analysis require computers?

[@DrWD40]

Helps make it easier but you can measure Rf values of the bands on the gel as well

[@مربدمحمدقاسم]

I have questions??

[@DrWD40]

yes?