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# E-values

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### #1 Kami23

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Posted 04 November 2009 - 06:43 AM

Hey all this is not my usual haunt but I have a question.... I have been aligning my protein sequence , trying to find a homologue in a different species. The problem is its a bit fragmented and for a portion of it i have an e-value of e-139. What does this mean?

Kami

### #2 lab rat

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Posted 04 November 2009 - 08:02 AM

If I understand e-values correctly, e-values approaching zero are highly significant on long(er) sequences. Short sequences are more likely to have a greater number of matches in a database, some random, so the e-value is greater and significance is less.
42..."An immutable fixed-precision number of unlimited magnitude." <a href="http://en.wikipedia....amming_language)" target="_blank">http://en.wikipedia....amming_language)</a>, accessed 25June2009.

### #3 phage434

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Posted 04 November 2009 - 08:11 AM

Low E values indicate high degrees of similarity -- they are the expected probability that the sequences are unrelated. An E value of 1 means that the match is probably random or chance. An E value of E-139 means almost absolute certainty that these are highly related sequences.

### #4 Kami23

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Posted 04 November 2009 - 08:42 AM

Low E values indicate high degrees of similarity -- they are the expected probability that the sequences are unrelated. An E value of 1 means that the match is probably random or chance. An E value of E-139 means almost absolute certainty that these are highly related sequences.

Thank you so much guys! You may have just opened up my portal to working in a froggy world! (i needed to know if my gene is in xenopus... im not smoking anything weird)