How do you find a primer to do PCR for unknown DNA sample from crime scene?

Basil_Fawlty

Hi

We had a genetics lecture today and I'm just wondering, if a primer is needed to carry out PCR, the sequence at the 5' end of each strand must be known so that the correct primer will fit.

However, from a crime scene, for example, how do they get an appropriate primer to amplify via PCR? If they don't know the sequence then how do they amplify the amount of DNA present by PCR to allow for subsequent sequencing?

tr3mor

I'm sorry, I thought this site was about moneysaving!

I'm not sure you'll find anyone here to help you!

Basil_Fawlty

tr3mor wrote:

I'm sorry, I thought this site was about moneysaving!

I'm not sure you'll find anyone here to help you!

There are a few Molecular Biologists on this board who helped me out a lot with my last topic :beer:

Nothing like positive thinking eh? That ^ , is nothing like postive thinking :rotfl:

tr3mor

Basil_Fawlty wrote:

There are a few Molecular Biologists on this board who helped me out a lot with my last topic :beer:

Nothing like positive thinking eh? That ^ , is nothing like postive thinking :rotfl:

Well how about you direct the question at them?

I'm still not sure I see what place this has on a board about money saving. Surely there are better places on the net to ask questions like this!

cowboy

I actually did this forensic practical last year but I forgot most of it! Shame on me....

Anyway, I suggest you to read about short tandem repeats (your lecturer might be covering this in more details):
http://en.wikipedia.org/wiki/Short_tandem_repeats

and here as well:
http://www.biology.arizona.edu/Human_Bio/activities/blackett2/str_description.html


I hope that answers your question.:T

RoCas

You trying to plan the perfect murder? :-)

LeanneF

Basil_Fawlty wrote:

If they don't know the sequence then how do they amplify the amount of DNA present by PCR to allow for subsequent sequencing?

Just to expand on Cowboy's response & to answer your question explicity...our genome has loads of things called 'short tandem repeats'. These are sequences of a few bases which are repeated over & over again. Because we know the sequence of the short tandem repeats we can design the PCR primer. What varies among individuals is not the sequence of these repeats, rather the number of them, say I might have 20 copies of the sequence repeated one after the other where as you might have 30 copies.

BTW, this is a very good question...don't be worried about asking your tutors or lecturers such questions, it demonstrates you're thinking which is what they want!

Crazyangel

RoCas wrote:

You trying to plan the perfect murder? :-)

:rotfl: LOL

pavlovs_dog

RoCas wrote:

You trying to plan the perfect murder? :-)

if so then tr3mor had best watch out :rotfl:

tr3mor

pavlovs_dog wrote:

if so then tr3mor had best watch out :rotfl:

:eek: !

Basil_Fawlty

Thank you for your replies - I'm much better informed about this now. :T :T :T

Cheers :beer:

P.S: tr3mor... if you hear a-knocking at the door in the a-middle of the a-night... you know it's me, with a large garden gnome... :eek: