Monday, February 4, 2013

Medical Mondays: Where IS this DNA stuff?


Hey guys! Thanks again for helping me celebrate the cover reveal of CONTROL last week! I am totally floored by the positive comments and the support. Thank you guys so much! There's still time to try to win a signed ARC and necklace Swag Packs, if you missed out. :)

So today, I have a great Medical Mondays question from writer Clara Waibel, who asks:

If someone is attacked, and gets some part of their body scratched, how long until the DNA of the offender vanishes? Would it take just a shower? Or does it remain in the victim's body for a longer period (assuming the victim is still alive)?

So where IS your DNA? We know it's in the cells of your body, but what about fluids? On your skin? Urine? Spit?

DNA, as you all probably know, are the the coding molecules found inside of the nucleus in your body's cells. So. No cell, no DNA. No nucleus, no DNA. As to how DNA can be detected, here are some facts:

Saliva: Your saliva is mostly water, proteins, and electrolytes with some shed cells from the inside of your mouth, so yes, it has DNA. Commonly, DNA samples are taken from scrapings from the inside part of your cheek, in your mouth. 

Blood: Yep, lots of DNA. But here's an interesting fact--the red blood cells that comprise most of the cells in your blood? They don't have a nucleus, and hence, have no DNA. But your white blood cells (aka infection fighting cells) do, and that's where DNA from blood samples come from. Also, platelets don't have nuclei either.

Urine: Your urine probably has some shed cells from the lining of your urinary tract, but usually it's a very small quantity.

Feces: You had to ask, didn't you? Well, you probably have some shed cells from the lining of your intestinal tract, but you also have tons of bacteria with their own DNA too (don't freak out! It's your natural flora. Yes, you are host to a raging party of happy bacteria in there. Fun.)

Skin: The surface of you skin is comprised of compressed skin cells, and yes, they have DNA still in them. In fact, now they can test surfaces you've just touched for DNA (source: Forensic Mag)

Hair: Your hair shaft is made of keratin, a kind of protein. No DNA. However, the follicle from which your hair grows out often comes loose when a hair falls or is pulled from your head. DNA samples can be taken from those follicles.

So going back to Clara's question. If an attacker scratched someone, that victim might have some DNA from his skin on them, but after a shower, it would likely be gone. Also, if there was broken skin (as in, the attackers DNA somehow got inside the victim, such as by blood-to-blood contact), the victim's defenses would destroy that DNA and the cells that crossed into her blood stream.

Thanks for a great question, and have a good Monday everyone!

****


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   All I ask is that you become a follower and post a link on your blog when I post your answer. This is for fictional scenarios, only. Please check out the boring but necessary disclaimer on my sidebar. :)

33 comments:

Old Kitty said...

Now I see why victims must not shower or bathe until they are thoroughly examined so the perpetrator's DNA won't be washed away! Yay! Take care
x

Shelly said...

Fascinating- I learned some new things today, which I love doing!

Natalie Aguirre said...

Great question. I had no idea blood doesn't have DNA.

Meredith said...

Huh, this is fascinating! I always wondered about where DNA is.

B.E. Sanderson said...

Another great post, Lydia. =o)

Jay Noel said...

Fascinating.

I worked in blood diagnostics for a little while. One thing I learned: you REALLY don't ever want to get a blood transfusion unless you will die without one.

So glad I know where my DNA is now, other than the three kids I have running amok.

Charley said...

Good details. Thanks!

Slamdunk said...

Excellent Dr.

IN terms of criminal justice, investigators don't want victims or potential suspects washing their hands before everything possible is collected and preserved.

TheReadingPenguin said...

Great post! Former Biology Major here--you'd be surprised what you can pull DNA out of. One of my sophomore classes was cell bio, and most of our big lab projects involved getting the DNA out of things--plants, animal tissue, processed food (seriously, Doritos have DNA. mostly from corn. yeah.)--and it's actually a huge pain in the butt. Total respect for the forensic folk that have to do that all of the time.

Alex J. Cavanaugh said...

Good to know!
Glad the cover reveal was a big hit last week. I feel really bad I missed helping you though.

Rachna Chhabria said...

Interesting post, Lydia! I learnt something new today.

Btw..I loved the cover of Control. Its super awesome.

Linda Gray said...

That is great information, thanks! Also important re not washing the attacker's DNA off before it's been collected. Horrible thought, but important. (btw., I did miss the cover reveal last week, but just checked it out. That is gorgeous! And since I just did a post on what I recently learned about covers that are designed for book discoverability, I'm so impressed with what your designer did. Really well done!)

LTM said...

WOW! This is a great question! And such useful info. So no DNA in hair, eh? Good to know... And it can wash off. *making notes* *for a book!!!*

And LOVE the cover of Control! *squee* :D <3

Barbara Watson said...

So interesting. My daughter 'made' a DNA molecule last week with beads and pipe cleaners to show the structure and how the nucleotide bases only attach to their partner base. It really helped her understand the whole thing.

Clarissa Draper said...

Very interesting. I'm surprised a person can get away with murder as easily as they do.

Karen Lange said...

Thanks, Lydia, for the info. I wasn't aware of this. Happy Monday!

Casey L. Clark said...

This is a really interesting post! I shall have to file this away for future reference...very handy.
Thanks! :)

JEFritz said...

This will surely be helpful for thriller writers. Or people who want to leave a "gift" on someone's desk as a practical joke.

Elizabeth Seckman said...

I feel smarter now. Thanks!

Southpaw said...

Ooo, I like the idea of our defenses attacking and killing of foreign DNA.

Kelly Polark said...

Very interesting!

Connie Keller said...

Fascinating! Especially lately when I've been reading about Richard III and the mitochondrial DNA, etc.

LD Masterson said...

Ah. Good to know. Thanks.

SA Larsenッ said...

Ooh, good to know. Especially about the urine. NOT!! Haha... I love these posts.

Kerri Cuev said...

Huh, good to know! Interesting how they can test surfaces now. They must solve cases faster, let's hope anyway.

nutschell said...

wow. awesome info, LYdia! I'm bookmarking this for future reference . :D

Nutschell
www.thewritingnut.com

mauricem1972 said...

CSI makes it sound like DNA is indestructible. Great insight Lydia.
- Maurice

alexia said...

Very interesting! I always love these medical posts. Reminds me of the movie Gattaca.

Jennifer Hillier said...

Great question, fantastic answers! Saving this one for when I need to refer back to it. :)

Clara said...

Thanks a bunch Lydia, perfect explanation like always! You're simply the best!!
Cheers

A Lady's Life said...

Well this was interesting.

Carol Riggs said...

Fascinating!! I love biology stuff. And I'd either forgotten or I did NOT know red blood cells didn't have nuclei. Thanks for the info!

Eva Inka Nurmaisya said...


Banned complain !! Complaining only causes life and mind become more severe. Enjoy the rhythm of the problems faced. No matter ga life, not a problem not learn, so enjoy it :)

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