i just performed a BLAST search with a query protein sequence of unknown function. The top...

i just performed a BLAST search with a query protein sequence of unknown function. The top hit was an alcohol dehydrogenase sequence with an E value of 6x10^-12. What does this result suggest about your query sequence and why?

i just want to know

the meaning of the e value

like what the e value depicts

Expert Solution

The Expect value (E) is a parameter that describes the number of hits one can "expect" to see by chance when searching a database of a particular size. It decreases exponentially as the Score (S) of the match increases. Essentially, the E value describes the random background noise. For example, an E value of 1 assigned to a hit can be interpreted as meaning that in a database of the current size one might expect to see 1 match with a similar score simply by chance.

The lower the E-value, or the closer it is to zero, the more "significant" the match is. However, keep in mind that virtually identical short alignments have relatively high E values. This is because the calculation of the E value takes into account the length of the query sequence. These high E values make sense because shorter sequences have a higher probability of occurring in the database purely by chance.

The Expect value can also be used as a convenient way to create a significance threshold for reporting results. You can change the Expect value threshold on most BLAST search pages. When the Expect value is increased from the default value of 10, a larger list with more low-scoring hits can be reported.

venereology answered 1 year ago

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