P. A larger E-value indicates higher sequence similarity
Q. E-value < $10^{-10}$ indicates sequence homology
R. A higher BLAST score indicates higher sequence similarity
S. E-value > $10^{10}$ indicates sequence homology
Q and R only
BLAST Algorithm: Evaluating Sequence Similarity Statements
This solution analyzes the correctness of statements regarding the BLAST algorithm's output, specifically focusing on E-value and BLAST score interpretation during sequence similarity searches.
Statement Analysis
-
Statement P: A larger E-value indicates higher sequence similarity
This statement is incorrect. The E-value represents the number of alignments with a certain score expected to occur by chance in a database. A larger E-value implies a higher probability of a random match, thus indicating *lower* sequence similarity or significance.
-
Statement Q: E-value < $10^{-10}$ indicates sequence homology
This statement is correct. An extremely low E-value, such as less than $10^{-10}$, signifies a statistically significant match. This low probability of occurring by chance strongly suggests that the sequences share a common ancestor, i.e., they are homologous.
-
Statement R: A higher BLAST score indicates higher sequence similarity
This statement is correct. The BLAST score directly reflects the quality of the alignment between the query and the database sequence. Higher scores correspond to better alignments, indicating greater sequence similarity.
-
Statement S: E-value > $10^{10}$ indicates sequence homology
This statement is incorrect. An E-value greater than $10^{10}$ is extremely large, meaning it's highly probable that the observed alignment occurred purely by chance. Such high E-values do not provide evidence for sequence homology.
Conclusion
Based on the analysis, statements Q and R are correct.
- Q is correct because a very low E-value suggests statistical significance, implying homology.
- R is correct because a higher score signifies a better alignment, indicating more similarity.
Therefore, the correct option includes only statements Q and R.
Important Questions from Molecular Structure of Genes and Chromosomes
Consider the following multiple sequence alignment of four DNA sequences.
$\begin{matrix}A & C & T & A \\ A & C & T & G \\ A & G & T & C \\ A & G & C & T \end{matrix} $
Shannon's entropy of the above alignment is ________.
- All pseudogenes DO NOT code for a __________.
- C-value paradox refers to
The transcription factor X binds a 10 base pair DNA stretch. In the DNA of an organism, X was found to bind at 20 distinct sites. An analysis of these 20 binding sites showed the following distribution:
Base Position in the binding site 1 2 3 4 5 6 7 8 9 10 A 11 0 0 0 16 2 4 0 4 3 T 3 0 19 0 1 3 4 20 2 4 G 4 20 0 0 2 4 6 0 12 2 C 2 0 1 20 1 11 6 0 2 11 What is the consensus sequence for the binding site of X?
- Which one of the following DNA sequences carries an invert repeat?
