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Name: Saundra
Status: Educator
Age: 30s
Location: N/A
Country: N/A
Date: N/A 


Question:
Is it possible to obtain DNA from human blood consumed by a mosquito, recognizing (I think) that the red blood cells have no nuclei, and so wouldn't carry DNA, whereas white blood cells would?

Would the ability to derive a DNA sample be dependant on the mosquito having comsumed white blood cells? And if it is possible, would the digestive breakdown of the blood by the mosquito render it impossible to extract the DNA, and if so, after what period of time ie for how long after drawing the blood would the DNA remain sufficiently constituted?



Replies:
A good question, Saundra,

Jurassic Park has many people thinking about related issues! You correctly note that red cells (RBCs) lack a nucleus, thus providing no genetic encyclopedia of their history. However, a given volume of human blood contains about 45% RBCs, about 1% platelets & white cells (WBCs); the rest is plasma. Therefore for every 45 RBCs, you'll also get 1 WBC, on average. The volume taken in by a mosquito can therefore contain LOTS of WBCs and ample opportunity to sample the DNA. As to the issue of how long it would take digestive enzymes present in the mosquito gut to render the DNA unreadable, which I think would doubtless happen sooner or later... I have no idea. Several variables here: specificity of the enzymes, temperature, etc. Hopefully an entomologist out there will read your question & provide us some information about that.

Thanks,
CED


You're correct that red blood cells contain no DNA and that white blood cells do carry DNA. And you're also correct that the mosquito would have to ingest white blood cells. However, I think it's pretty unlikely with the tiny volume of blood that a single mosquito would consume that there'd be enough human cells present to extract a DNA sample. Also, I can't imagine how you'd recover the blood that a mosquito has ingested without a tremendous contamination with mosquito cells (therefore mosquito DNA).

If you wanted to do a weird experiment like extracting DNA from mosquitoes to look for evidence of human blood, you'd need a lot of mosquitoes (a hundred per DNA sample?). You could grind them all up whole to make DNA from the whole population. Then by using PCR (polymerase chain reaction) you could try to amplify a common human gene like a ribosomal gene. I don't know if it would work, but it might be cool to try.

Christine Ticknor
Ph.D. Student
Yale University
New Haven, Connecticut



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