Question

Z-score describes the number of standard deviations from the mean score for the database search.

(a) True

(b) False

This question was posed to me in an interview.

The above asked question is from FASTA topic in division Database Similarity Searching of Bioinformatics

Answer 1

Correct answer is (a) True

To explain: Because most of the alignments with the query sequence are with unrelated sequences, the higher the Z-score for a reported match, the further away from the mean of the score distribution, hence, the more significant the match. For a Z-score > 15, the match can be considered extremely significant, with a certainty of a homologous relationship. If Z is in the range of 5 to 15, the sequence pair can be described as highly probable homologs. If Z<5, their relationship is described as less certain.