Final answer:
In a BLAST search, the E-value helps to determine the significance of matches between query and database sequences, with values close to zero indicating high significance. Query coverage shows the proportion of the query sequence that aligns, while identity shows the percentage of exact matches in the alignment.
Step-by-step explanation:
In BLAST searches, the E-value, or Expected value, is a statistical parameter that indicates the number of hits one can expect to see by chance when searching a database of a particular size. It helps in determining the significance of the match between the query sequence and database sequences. An E-value close to zero suggests a highly significant match, whereas a larger E-value indicates a less significant match. Query coverage refers to the percentage of the query sequence that is included in the alignment, indicating how much of your sequence has been matched to database sequences.
Identity refers to the percentage of nucleotides or amino acids in the alignment that are identical between the query and the subject sequences. High identity usually signifies close relatedness. The process involves aligning the sequence into words, finding the highest scoring arrangements and then extending the alignment for the best overall match. Random similarity is accounted for by the E-value to avoid false-positive results.
When evaluating the E-values for alignments with different subjects such as Bacillus subtilis subsp. spizizenii, Pseudomonas stutzeri, or Exiguobacterium sibiricum, a lower E-value would be indicative of a more significant and reliable alignment, suggesting less chance of the similarity being due to random chance.