Bio Informatics Question:

Expect value. The E-value 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 with the score (S) that is assigned to a
match between two sequences. Essentially, the E-value
describes the random background noise that exists for
matches between sequences. 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 one
match with a similar score simply by chance. This means
that the lower the E-value, or the closer it is to “0”, the
higher is the “significance” of the match. However, it is
important to note that searches with short sequences can be
virtually identical and have relatively high E-value. This
is because the calculation of the E-value also takes into
account the length of the query sequence. This is because
shorter sequences have a high probability of occurring in
the database purely by chance